M O D U L A R
S Y S T E M
OXYGEN and NITROGEN containing ORGANIC COMPOUNDS Ayhan NAZLI Murat DURKAYA Yener EKÞÝ Nuh ÖZDÝN Muhammet AYDIN Davut PÝRAZ Necdet ÇELÝK Uður Hulusi PATLI Varol GÜRLER
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Chemistry is an interesting and fundamental branch of science because it gives us the chance to explain the secrets of nature. What is water? What do we use in our cars as fuel? What is aspirin? What are perfumes made of? Many of these kinds of questions and their answers are all part of the world of chemistry. chemistry. There is no industry that does not depend upon chemical substances; petroleum, pharmaceutical, garment, aircraft, steel, electronics, agricultural, etc. This book helps everyone to understand the chemistry in nature. However, one does not need to be a chemist or scientist to understand the simplicity within the complexity around us. The aim was to write a modern, up-to-date book where students and teachers can find concise information about the structure of substances. Sometimes reactions are given in detailed form, but, in all, excessive detail has been omitted. The book is designed to introduce basic knowledge about organic compounds containing oxygen and nitrogen. Chemists work everyday to produce new compounds to make our lives easier with the help of this basic knowledge. In the design, emphasis has been been placed placed upon upon making making the the book student friendly. Throughout the books, colorful tables, important reactions, funny cartoons, interesting extras and reading passages are used to help explain ideas. This book will also show you how many organic compounds are important to us in our everyday lives. We hope that after studying this book you will find organic chemistry in every part of your life. The authors would like to thank Orhan Keskin, Ali Çavdar and Ramazan Þahin for their support and encouragement throughout the development of this book. We would also like to thank Tekin Çorbalý, Mustafa Yýlmaz and Okan Çeliker for their thoughtful criticisms and helpful suggestions to the manuscript which have been of such great value in developing the book. Many people have assisted us in writing these books. We wish to gratefully acknowledge the contributions of Þerafettin Küçükoðlu, Faik Bolat and Sani Demiri for their reviews and suggestions. We are particularly grateful to our spouses and children for their patience during the writing of the book. The Authors
Chapter 1
5.
5.1. SYNTHESIS SYNTHESIS OF ALCOH ALCOHOLS OLS FROM FROM ALKENES . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
ALCOHOLS AND ETHERS INTRODUCTION TO ALCOHOLS . . . . . . . . . . . . . . . 10 1.
5.2. SYNTHE SYNTHESIS SIS OF ALCOH ALCOHOLS OLS FROM FROM ALKYL HALIDES . . . . . . . . . . . . . . . . . . . . . . . . . 37
CLASSI CLA SSIFIC FICAT ATIO ION N OF OF ALCO ALCOHO HOLS LS . . . . . . . . . . 12
5.3. SYNTHESIS SYNTHESIS OF ALCO ALCOHOLS HOLS BY BY THE REDUCTION OF ALDEHYDES, KETONES AND CARBOXYLIC ACIDS . . . 37
1.1. ACCORDI ACCORDING NG TO THE NUMBER NUMBER OF – OH GROUP . . . . . . . . . . . . . . . . . . . . . . . . 12 Monohydric Monohy dric Alcohols Alcohols . . . . . . . . . . . . . . . . . . . . . . 12
5.4. SYNTHESIS SYNTHESIS OF ALCOH ALCOHOLS OLS USING USING GRIGNARD REAGENTS . . . . . . . . . . . . . . . 37
Polyhydric Polyh ydric Alcohols Alcohols . . . . . . . . . . . . . . . . . . . . . . . 12 1.2. ACCORDI ACCORDING NG TO THE THE CARBON CARBON ATOM HAVING THE –OH GROUP . . . . . . . 12
6.
SOME SO ME IMP IMPOR ORT TAN ANT T ALCO ALCOHO HOLS LS . . . . . . . . . . . . 39 6.1.. MET 6.1 METHYL HYL ALCO ALCOHOL HOL . . . . . . . . . . . . . . . . . . 39
Primary (1°) (1°) Alcohols Alcohols . . . . . . . . . . . . . . . . . . . . . . 12
Physical Properties. Properties. . . . . . . . . . . . . . . . . . . . . . . . 39
Secondary (2°) Alcohols. . . . . . . . . . . . . . . . . . . . 13
Chemical Chemic al Properties Properties . . . . . . . . . . . . . . . . . . . . . . . 40
Tertiary (3°) (3°) Alcoho Alcohols ls . . . . . . . . . . . . . . . . . . . . . . . 13 2.
PREP PRE PARA ARATIO TION N OF ALC ALCOHO OHOLS LS.. . . . . . . . . . . . . 36
Synthesis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
NOMENC NOM ENCLA LATUR TURE E OF ALC ALCOHO OHOLS LS . . . . . . . . . . 13 2.1.. CO 2.1 COMMO MMON N NAMES NAMES . . . . . . . . . . . . . . . . . . . 13
6.2.. ETH 6.2 ETHYL YL ALCO ALCOHOL HOL . . . . . . . . . . . . . . . . . . . . 41
2.2. USIN USING G THE IUPA IUPAC C SYSTEM SYSTEM . . . . . . . . . . . 14
Physical Properties. Properties. . . . . . . . . . . . . . . . . . . . . . . . 41
3.
PHYSIC PHY SICAL AL PROP PROPERT ERTIES IES OF ALC ALCOHO OHOLS LS . . . . 17
Chemical Chemic al Properties Properties . . . . . . . . . . . . . . . . . . . . . . . 42
4.
CHEMIC CHE MICAL AL PRO PROPER PERTIE TIES S ALCO ALCOHOL HOLS S . . . . . . . 22
Synthesis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 6.3.. GL 6.3 GLYC YCOL OL . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.1. REACTIONS OF ALCOHOLS INVOL INVOLVING VING O–H BOND BREAKAGE . . . . . . . . . . . . . . . 22
Readin Rea ding g : Life in the Poles. . . . . . . . . . . . . . . . . . 46 6.4.. GL 6.4 GLYC YCERI ERINE NE . . . . . . . . . . . . . . . . . . . . . . . . . 47
Reaction of Alcohol with Alkali Metals . . . . . . . . . 23 Esterificati Esteri fication on Reactions Reactions . . . . . . . . . . . . . . . . . . . . 25
7.
INTR IN TROD ODUC UCTI TION ON TO ET ETHE HERS RS . . . . . . . . . . . . . . 47
4.2. REACTIONS OF ALCOHOLS INVOL INVOLVING VING C–O BOND BREAKAGE . . . . . . . . . . . . . . . 27
8.
NOME NO MENC NCLA LATU TURE RE OF OF ETHE ETHERS RS . . . . . . . . . . . . . 49 8.1.. CO 8.1 COMMO MMON N NAMES NAMES . . . . . . . . . . . . . . . . . . . 49
Reaction Reacti on of Alcohols Alcohols with Hydrogen Hydrogen Halides Halides . . . 28 Dehydration Dehyd ration of Alcohols Alcohols . . . . . . . . . . . . . . . . . . . . 29 4.3. OXI OXIDA DATION TION OF ALCOHO ALCOHOLS LS.. . . . . . . . . . . . 31 Oxidation Oxidat ion of Primary Alcohols Alcohols . . . . . . . . . . . . . . . 32 Oxidation of Secondary Alcohols. . . . . . . . . . . . . 32 Oxidation of Tertiary Alcohols. . . . . . . . . . . . . . . . 32 4.4. COMBUSTI COMBUSTION ON REACTIONS REACTIONS OF OF ALCOHOLS . . . . . . . . . . . . . . . . . . . . . . . . . 35
8.2. IUPAC SYSTEM . . . . . . . . . . . . . . . . . . . . . . 50 9.
PHYSIC PHY SICAL AL PRO PROPER PERTIE TIES S OF OF ETHE ETHERS RS . . . . . . . 50
10. CHEMI CHEMICAL CAL PROPERTI PROPERTIES ES OF ETHERS ETHERS . . . . . . 52 11. PREP PREPARA ARATION TION OF ETHERS ETHERS . . . . . . . . . . . . . . . 53 Dehydration Dehydr ation of Alcohols Alcohols . . . . . . . . . . . . . . . . . . . . 53 The Williamson Synthesis of Ethers. . . . . . . . . . . 54 12.. DIE 12 DIETHY THYL L ETHER ETHER . . . . . . . . . . . . . . . . . . . . . . . . . 54
SUPPLEMENTARY QUESTIONS . . . . . . . . . . . . . . . 55
6.2.. AC 6.2 ACET ETALD ALDEHY EHYDE DE.. . . . . . . . . . . . . . . . . . . . . 83
MULTIPLE CHOICE QUESTIONS . . . . . . . . . . . . . . . 58
7.
KETONES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
8.
NOME NO MENC NCLA LATU TURE RE OF OF KETON KETONES ES.. . . . . . . . . . . . 85
PUZZLE
8.1.. CO 8.1 COMMO MMON N NAMES NAMES . . . . . . . . . . . . . . . . . . . 85 8.2. USIN USING G THE IUPA IUPAC C SYSTEM SYSTEM . . . . . . . . . . . 85
Chapter 2
9.
ALDEHYDES AND KETONES INTRODUCTION.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 INTRODUCTION 1.
ALDEHYDES . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
2.
NOMENC NOM ENCLA LATUR TURE E OF ALD ALDEHY EHYDES DES . . . . . . . . . 65
3.
PHYSICAL PHYSIC AL PRO PROPER PERTIE TIES S OF DES 67
ALDEHY ALD EHY--
4.
CHEMICAL CHEMIC AL PRO PROPER PERTIE TIES S OF DES 68
ALDEHY ALD EHY--
4.1. OXI OXIDA DATION TION REACT REACTIONS IONS . . . . . . . . . . . . . . 68 Tollens’ Test Test (Silver Mirror Test) . . . . . . . . . . . . . . 69 Fehling’s Fehli ng’s Test Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 71 Reactions with KMnO4 . . . . . . . . . . . . . . . . . . . . . 72 4.2. ADDITION ADDITION REAC REACTION TIONS S OF ALDEHYALDEH YDES.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 DES Addition of Hydrogen . . . . . . . . . . . . . . . . . . . . . . 73 Addition of Water . . . . . . . . . . . . . . . . . . . . . . . . . 74 Addition of Alcohol . . . . . . . . . . . . . . . . . . . . . . . . 75 Addition of HCN . . . . . . . . . . . . . . . . . . . . . . . . . . 76
10.1.. ADDIT 10.1 ADDITION ION REAC REACTION TIONS S . . . . . . . . . . . . . 88 Addition of Hydrogen (Reduction of Ketones). . . 88 Addition of Water . . . . . . . . . . . . . . . . . . . . . . . . . 88 Addition of Alcohol . . . . . . . . . . . . . . . . . . . . . . . . 89 Addition of HCN . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Addition of Grignard Reagents. . . . . . . . . . . . . . . 90 Addition of NaHSO 3 . . . . . . . . . . . . . . . . . . . . . . . 90 10.2. COMBUSTION REACTION . . . . . . . . . . . . 95 11. PREP PREPARA ARATION TION OF KETONES KETONES . . . . . . . . . . . . . 95 11.1. OXIDA OXIDATION TION OF SECONDARY ALCOHOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 11.2. DEHYDROGENA DEHYDROGENATION TION OF SECONDARY SECONDARY ALCOHOLS . . . . . . . . . . . . . . . . . . . . . . . . . 96 11.3. HEATING CALCIUM SAL SALTS TS OF CARBOXYLIC ACIDS. ACIDS . . . . . . . . . . . . . . . . . . . . . 96 11.4. ADDITION OF WATER WATER TO ALKYNES ALKYNES.. . . . 96 12.. AC 12 ACET ETON ONE E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Addition of NaHSO 3 . . . . . . . . . . . . . . . . . . . . . . . 77
12.1. PREPA PREPARATION RATION OF ACETONE ACETONE . . . . . . . . . 97
4.4. COMB COMBUSTIO USTION N REACTIO REACTION N . . . . . . . . . . . . . 78 PREP PRE PARA ARATIO TION N OF OF ALD ALDEHY EHYDES DES . . . . . . . . . . . 79 5.1. OXIDA OXIDATION TION OF PRIMA PRIMARY RY ALCO-ALCO HOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 5.2. DEHYROGENA DEHYROGENATION TION OF PRIMARY PRIMARY ALCOHOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 6.
10. CHEM CHEMICAL ICAL PROPERTI PROPERTIES ES OF KETONES KETONES . . . . . 88
Addition of Grignar d Reagents. . . . . . . . . . . . . . . 76
4.3. POL POLYMERI YMERISA SATION TION . . . . . . . . . . . . . . . . . . . 78
5.
PHYSIC PHY SICAL AL PROP PROPERT ERTIES IES OF KET KETONE ONES S . . . . . 86
SOME SO ME IMPO IMPORT RTAN ANT T ALDEH ALDEHYD YDES ES . . . . . . . . . . . 81 6.1.. FOR 6.1 FORMA MALDE LDEHYD HYDE E . . . . . . . . . . . . . . . . . . . . 81
Distillation of Wood. . . . . . . . . . . . . . . . . . . . . . . . 97 Heating of Calcium Acetate. . . . . . . . . . . . . . . . . 97 Oxidation of Isopropyl Alcohol . . . . . . . . . . . . . . . 97 From Acetic Acetic Acid . . . . . . . . . . . . . . . . . . . . . . . . . 98 98 SUPPLEMENTARY SUPPLEMENTA RY QUESTIONS . . . . . . . . . . . . . . . 99 MULTIPLE CHOICE QUESTIONS . . . . . . . . . . . . . . 102 PUZZLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
5.2. OXIDATION OF AROMATIC COMPOUNDS . . . . . . . . . . . . . . . . . . . . . .123
Chapter 3
CARBOXYLIC ACIDS
5.3. OXIDATION OF ALKENES . . . . . . . . . . . .124
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . .108 1.
CLASSIFICATION OF CARBOXYLIC ACIDS .108
5.4. CARBONATION OF GRIGNARD REAGENTS . . . . . . . . . . . . . . . . . . . . . . . .124
1.1. ACCORDING TO NUMBER OF CARBOXYL GROUPS . . . . . . . . . . . . . . . .108
5.5. HYDROLYSIS OF CARBOXYLIC ACID DERIVATIVES . . . . . . . . . . . . . . . . . . . . . . .124
Monocarboxylic Acids . . . . . . . . . . . . . . . . . . . .108
5.6. HYDROLYSIS OF NITRILES . . . . . . . . . . .125
Polycarboxylic Acids . . . . . . . . . . . . . . . . . . . . . .108
5.7. REACTION OF CARBOXYLATE SALTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125
1.2. ACCORDING TO THE FUNCTIONAL GROUPS . . . . . . . . . . . . . . . . . . . . . . . . . . .109
2.
6.
Hydroxy Acids . . . . . . . . . . . . . . . . . . . . . . . . . . .109
6.1. FORMIC ACID . . . . . . . . . . . . . . . . . . . . . .126
Amino Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . .109
Physical Properties . . . . . . . . . . . . . . . . . . . . . . .126
Keto Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109
Chemical Properties . . . . . . . . . . . . . . . . . . . . . .126
NOMENCLATURE OF CARBOXYLIC ACIDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109
Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127 Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .128
2.1. COMMON NAMES . . . . . . . . . . . . . . . . . .109
6.2. ACETIC ACID . . . . . . . . . . . . . . . . . . . . . . .128
2.2. USING THE IUPAC SYSTEM . . . . . . . . . .110 3.
PHYSICAL PROPERTIES OF CARBOXYLIC ACIDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112
4.
CHEMICAL PROPERTIES OF CARBOXYLIC ACIDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .116
Physical Properties . . . . . . . . . . . . . . . . . . . . . . .128 Chemical Properties . . . . . . . . . . . . . . . . . . . . . .128 Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .129 Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .130 Reading : Unsaturated Carboxylic Acids and Their Polymers . . . . . . . . . . . . .130
4.1. REACTION INVOLVING CLEAVAGE OF THE O–H BOND . . . . . . . . . . . . . . . . .116 Salt Formation . . . . . . . . . . . . . . . . . . . . . . . . . . .116
7.
DICARBOXYLIC ACIDS . . . . . . . . . . . . . . . . . .132
Neutralization Reactions . . . . . . . . . . . . . . . . . . .117
7.1. OXALIC ACID . . . . . . . . . . . . . . . . . . . . . . .132
Reactions with Salts . . . . . . . . . . . . . . . . . . . . . .118
Physical Properties . . . . . . . . . . . . . . . . . . . . . . .132
4.2. REACTIONS THAT INVOLVE C–O BOND BREAKAGE . . . . . . . . . . . . . . . . . .119
Chemical Properties . . . . . . . . . . . . . . . . . . . . . .132 Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .133
Formation of Acid Anhydrides . . . . . . . . . . . . . .119
Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .133
Esterification . . . . . . . . . . . . . . . . . . . . . . . . . . . .120
7.2. MALONIC ACID . . . . . . . . . . . . . . . . . . . . .133
Formation of Acid Chlorides . . . . . . . . . . . . . . . .121 4.3. ADDITION OF HALOGENS . . . . . . . . . . . .122 4.4. REDUCTION REACTIONS . . . . . . . . . . . .122 5.
SOME IMPORTANT CARBOXYLIC ACIDS . . .126
PREPARATION OF CARBOXYLIC ACIDS . . . .123 5.1. OXIDATION OF PRIMARY ALCOHOLS AND ALDEHYDES . . . . . . . . . . . . . . . . . . .123
7.3. ADIPIC ACID . . . . . . . . . . . . . . . . . . . . . . .134 8.
FATTY ACID . . . . . . . . . . . . . . . . . . . . . . . . . . . .134 8.1. SATURATED FATTY ACIDS . . . . . . . . . . .135 Palmitic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . .135 Stearic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135
9.
8.2. UNSATURATED FATTY ACIDS . . . . . . . .135
9.
CLEANING PROCESS OF SOAPS . . . . . . . . .166
Oleic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135
10. DETERGENTS . . . . . . . . . . . . . . . . . . . . . . . . . .167
Linoleic Acid and Linolenic Acid . . . . . . . . . . . .135
SUPPLEMENTARY QUESTIONS . . . . . . . . . . . . . .168
OXYACIDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .136
MULTIPLE CHOICE QUESTIONS . . . . . . . . . . . . . .172
Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .137
PUZZLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174
Carbonic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . .137 10. OPTICAL ISOMERISM . . . . . . . . . . . . . . . . . . .138 SUPPLEMENTARY QUESTIONS . . . . . . . . . . . . . .142 MULTIPLE CHOICE QUESTIONS . . . . . . . . . . . . . .147 PUZZLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .152
Chapter 4
Chapter 5
CARBOHYDRATES INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . .176 1.
STRUCTURE OF CARBOHYDRATES . . . . . . .176
2.
NOMENCLATURE OF CARBOHYDRATES . . .177
3.
CLASSIFICATION OF CARBOHYDRATES . . .178
ESTERS
3.1. MONOSACCHARIDES . . . . . . . . . . . . . . .178
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . .154
General Properties . . . . . . . . . . . . . . . . . . . . . . .178
1.
ESTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .154
Cyclic Structures of Monosaccharides . . . . . . .179
2.
NOMENCLATURE OF ESTERS . . . . . . . . . . . .154
Oxidation of Monosaccharides . . . . . . . . . . . . . .180
3.
PHYSICAL PROPERTIES OF ESTER . . . . . . .156
Reduction of Monosaccharides . . . . . . . . . . . . .184
4.
CHEMICAL PROPERTIES OF ESTERS . . . . . .158
3.2. DISACCHARIDES . . . . . . . . . . . . . . . . . . .186
4.1. HYDROLYSIS OF ESTERS . . . . . . . . . . . .158
General Properties . . . . . . . . . . . . . . . . . . . . . . .186
4.2. SAPONIFICATION OF ESTERS . . . . . . . .158
Saccharose (Sucrose) . . . . . . . . . . . . . . . . . . . .186
4.3. REDUCTION OF ESTERS . . . . . . . . . . . . .158
Lactose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .187
4.4. REACTION WITH AMMONIA . . . . . . . . . .159
Maltose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .187
PREPARATION OF ESTERS . . . . . . . . . . . . . . .160
Cellobiose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .188
5.1. FROM CARBOXYLIC ACID AND ALCOHOLS . . . . . . . . . . . . . . . . . . . . . . . .160
3.3. POLYSACCHARIDES . . . . . . . . . . . . . . . .188
5.
5.2. FROM CARBOXYLIC ACID DERIVATIVES . . . . . . . . . . . . . . . . . . . . . . .161 6.
FATS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162 6.1. CLASSIFICATION OF FATS . . . . . . . . . . .163 Vegetable Fats . . . . . . . . . . . . . . . . . . . . . . . . . .163 Animal Fats . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163 According to Their Physical States . . . . . . . . . .163
7.
HYDROGENATION AND MARGARINES . . . . .164
8.
SAPONIFICATION . . . . . . . . . . . . . . . . . . . . . .165
General Properties . . . . . . . . . . . . . . . . . . . . . . .188 Starch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .189 Glycogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .189 Dextrin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .189 Cellulose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .190 SUPPLEMENTARY QUESTIONS . . . . . . . . . . . . . .191 MULTIPLE CHOICE QUESTIONS . . . . . . . . . . . . . .193 PUZZLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .196
Trinitrotoluene . . . . . . . . . . . . . . . . . . . . . . . . . . .220
Chapter 6
AMINES, AMIDES AND AMINO ACIDS
3.
3.1. ANILINE . . . . . . . . . . . . . . . . . . . . . . . . . . .221
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . .198 1.
Preparation
AMINES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .198 1.1. NOMENCLATURE OF AMINES . . . . . . . .198
4.
5.
3.
. . . . . . . . . . . . . . . . . . . . . . . . . . . .223
AROMATIC ALDEHYDES . . . . . . . . . . . . . . . . .225 5.1. BENZALDEHYDE . . . . . . . . . . . . . . . . . . . .225 Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .225
1.4. PREPARATION OF AMINES . . . . . . . . . . .203 AMIDES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .204
AROMATIC ALCOHOLS . . . . . . . . . . . . . . . . . .223
Preparation
1.2. PHYSICAL PROPERTIES . . . . . . . . . . . . .201
2.
. . . . . . . . . . . . . . . . . . . . . . . . . . . .222
4.1. BENZYL ALCOHOL . . . . . . . . . . . . . . . . . .223
Common Names . . . . . . . . . . . . . . . . . . . . . . . . .198
1.3. CHEMICAL PROPERTIES AND REACTIONS . . . . . . . . . . . . . . . . . . . . . . . .202
AROMATIC AMINO COMPOUNDS . . . . . . . . .221
6.
AROMATIC CARBOXYLIC ACIDS . . . . . . . . . .226
2.1. NOMENCLATURE OF AMIDES . . . . . . . .205
6.1. BENZOIC ACID . . . . . . . . . . . . . . . . . . . . .227
2.2. PROPERTIES OF AMIDES . . . . . . . . . . . .205
Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .227
2.3. PREPARATION OF AMIDES . . . . . . . . . . .205
6.2. TEREPHTHALIC ACID . . . . . . . . . . . . . . .228
2.4. UREA (Carbamide) . . . . . . . . . . . . . . . . . .207
SUPPLEMENTARY QUESTIONS . . . . . . . . . . . . . .229
AMINO ACIDS . . . . . . . . . . . . . . . . . . . . . . . . . .207
MULTIPLE CHOICE QUESTIONS . . . . . . . . . . . . . .232
3.1. NOMENCLATURE OF AMINO ACIDS . . .207
PUZZLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .238
3.2. PROPERTIES OF AMINO ACIDS . . . . . . .208 PEPTIDE FORMATION AND PROTEINS . . . . .208
GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .240
Reading : Chemistry of Vision . . . . . . . . . . . . .209
ANSWERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .243
SUPPLEMENTARY QUESTIONS . . . . . . . . . . . . . .210
INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .255
MULTIPLE CHOICE QUESTIONS . . . . . . . . . . . . . .211
REFERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .256
4.
PUZZLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .214
Chapter 7
AROMATIC COMPOUNDS 1.
PHENOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .216 1.1. PHENOL . . . . . . . . . . . . . . . . . . . . . . . . . . .216
2.
AROMATIC NITRO COMPOUNDS . . . . . . . . . .218 2.1. GENERAL STRUCTURE . . . . . . . . . . . . . .218 2.2. NITRATION . . . . . . . . . . . . . . . . . . . . . . . . .219 Nitrobenzene . . . . . . . . . . . . . . . . . . . . . . . . . . . .219 Dinitrobenzene . . . . . . . . . . . . . . . . . . . . . . . . . .220
INTRODUCTION TO ALCOHOLS Alcohols are compounds whose molecules have a hydroxyl group (
OH)
attached to a saturated carbon atom. Alcohols can be described as alkyl derivatives of water where one hydrogen in the water molecule has been replaced by an alkyl (R
) group. The general formula of alcohols is R
OH and the gener-
al molecular formula of alcohols is C nH2n+1OH or C nH2n+2O. R
H
H
Alkane
Although hund reds of alcohols are
OH
R
Water
OH
Alcohol
known. When alcohol as a word is used
The functional group that determines an alcohol is
many people associate it only with ethyl
having the
alcohol (ethanol).
and is
sp3
OH. The carbon atom
OH group is attached to another carbon atom by a single bond
hybridised. The carbon chain of the rest of the alcohol can be saturat-
ed or unsaturated. The saturated carbon atom having the
OH group may:
a. be a carbon atom of a simple alkyl group, as in the following examples.
b. be from an alkenyl or alkynyl group, or it may be a saturated carbon atom attached to a benzene ring as in the following examples.
Blood Alcohol Level Affects on The Body and Behavior! The effects of drinking alcoholic beverages depend upon the amount of actual ethyl alcohol consumed and body weight. The level of alcohol in the blood is calculated in miligrams of pure ethyl alcohol per deciliter of blood and is commonly expressed as a percentage.
10
Blood Alcohol Level
Effect
0.02 – 0.02%
Changes in behavior and ability to think clearly
0.05%
Sedation and tranquilized feeling
0.08 – 0.10%
Legal intoxication in some countries.
0.15 – 0.20%
Person is obviously intoxicated and may show signs of delirium
0.30 – 0.40%
Loss of consciousness
0.50%
Heart and respiration become so depressed that they cease to function and death follows
Oxygen And Nitrogen Containing Organic Compounds
Compounds That Do Not Exhibit The Properties of Alcohols d. CH3COOH
Some compounds having the properties of alcohols.
OH group do not show the
1. Compounds in which the carbon atom bearing the
hydroxyl group is attached to a carbon atom with a double bond are called enols. Enols do not exhibit the properties of alcohols. The compound in which the hydroxyl group is attached to a benzene ring is called phenol.
HO
CH2
OH is an alcohol.
OH groups are attached to the same CH2
OH is not
an alcohol. It is an aldehyde hydrate.
d. The structural formula of CH 3COOH is
In this structure, the carbon atom that has the
OH
group is also bonded to oxygen with a double bond and is therefore unsaturated. So CH 3COOH is not an alcohol, it is a carboxylic acid.
CH2
carbon atom, the compound HO
The molecule in which one carbon atom has two OH groups is called an aldehyde hydrate or a ketone hydrate. If the carbon atom has three OH groups it is called a carboxylic acid hydrate.
OH group is saturated.
OH groups are attached to different sat-
c. Since the
OH group it is not an alcohol.
OH is an alcohol because the car-
urated carbon atoms, the compound
CH2
bon atom attached to the
3. In a molecule, if the same carbon atom has more than
CH
b. Since the
2. The carbon atom bearing the
one
Solution ——————————————————————————
OH group in carboxylic acids is not saturated. Carboxylic acids do not show properties of alcohols.
a. CH2
e.
that has the OH group is saturated, having the structure
Example —————————————————————————— Which of the following do not show the properties of an
is an alcohol because the carbon atom
f.
atom with the
is not an alcohol because the carbon OH group has a double bond.
alcohol?
a. CH2
CH
CH2
OH
b. HO
CH2
CH2
OH
c. HO
CH2
OH
Alcohols and Ethers
11
1. CLASSIFICATION OF ALCOHOLS Alcohols can be classified in two ways. The first classification is based on the number of hydroxyl groups in the molecule, the second is based on the condition of the carbon atom with the hydroxyl group.
1.1. ACCORDING TO THE NUMBER OF — OH GROUPS Alcohols can be classified as monohydric and polyhydric alcohols according to the number of
OH groups in their structure.
Monohydric Alcohols Alcohols containing only one hydroxyl group in their structure are called mono hydric alcohols.
Polyhydric Alcohols Alcohols containing two or more hydroxyl groups in their molecules are called polyhydric alcohols. Alcohols containing two or diols, and those with three
OH groups are called glycols
OH groups are called glycerols or triols.
1.2. ACCORDING TO THE CARBON ATOM HAVING THE — OH GROUP Alcohols can be classified as primary, secondary and tertiary alcohols according to the condition of the carbon atom to which the hydroxyl group is attached.
Primary (1°) Alcohols
If the carbon bearing the
OH group is attached to only one other carbon, that
carbon is said to be a primary carbon and the alcohol is a primary alcohol. Primary alcohols can be represented as:
Methyl alcohol which has only one car bon atom is considered a primary alco hol. 12
Some examples for primary alcohols are given below:
Oxygen And Nitrogen Containing Organic Compounds
is a primary carbon and accordingly the
compound is a primary alcohol.
Secondary (2°) Alcohols If the carbon with the
In a glycol molecule each carbon atom
OH group is attached to two other carbon atoms it is
called a secondary carbon and the alcohol is a secondary alcohol. An alcohol
needs at least three carbon atoms to be secondary.
The 1, 2 – propanediol molecule is a pri-
mary alcohol with respect to the first OH group, but a secondary alcohol with respect to the second
OH group.
Tertiary (3°) Alcohols If the carbon having the
OH group is attached to three other carbon atoms it
is called a tertiary carbon, and the alcohol is tertiary alcohol. In a tertiary alcohol, there are at least four carbon atoms.
Polyalcohols may be a combination of primary, secondary and tertiary depending on the positioning of each
OH group.
2. NOMENCLATURE OF ALCOHOLS 2.1. COMMON NAMES These are generally used for the simpler molecules of alcohols. Common names of alcohols are derived by naming the alkyl group attached to the
OH group
and then the word “alcohol” is added. The prefixes primary, secondary and tertiary may also be used.
Secondary = sec. Tertiary = tert.
Abbreviations in naming alcohols.
Alcohols and Ethers
13
1 Give the common names of the following compounds.
a. CH3CH2CH2CH2 b.
OH
c.
d. CH2
CH
CH2
OH
a. Since the alkyl group (C 4H9
) to which
OH is attached has a straight
chain structure , the compound is called n–butyl alcohol.
b. Since the carbon atom with the
OH group is attached to two other car-
bons, the compound is a secondary alcohol. The alkyl group (C 4H9
) is
butyl, so the name of the compound is sec-butyl alcohol.
c. Since the carbon atom that has the
OH group is bonded to three alkyl
groups, the compound is a tertiary alcohol. The alkyl group (C 5H11
) is
pentyl then the compound is named as tert-pentyl alcohol.
d. The unsaturated hydrocarbon derivative attached to the
OH group is
called propenyl, therefore the alcohol name is propenyl alcohol.
2.2. USING THE IUPAC SYSTEM The following procedure should be followed to name alcohols according to the IUPAC system. 1. Select the longest continuous carbon chain to which the hydroxyl group is attached. Change the name of the alkane corresponding to this chain by dropping the final –e and adding the suffix – ol. 2. Number the carbon atoms in the longest continuous carbon chain starting from the end nearest to the hydroxyl group. The carbon atom bearing the hydroxyl group takes the lower number. Indicate the position of the hydroxyl 14
Oxygen And Nitrogen Containing Organic Compounds
group by using this number; indicate the position of other substituents (as prefixes) by using the numbers corresponding to their positions along the carbon chain.
For straight chained compounds, if the
OH is attached to the first carbon,
instead of number “1”, the letter “n”, meaning normal, can be used. If the
OH group is attached to an unsaturated hydrocarbon chain, the num-
ber of the carbon bearing the
OH group is substituted between the name of
hydrocarbon and the suffix –ol. If the
OH group is attached to the first carbon
of the unsaturated hydrocarbon chain, the number of the carbon bearing the OH group is not written.
If the
OH group is in the middle of the chain, the numbering of the carbon
atoms starts at the end nearest any branching.
If there are more than one
OH group, “di, tri, tetra....” are used before the suf-
fix –ol. The numbers of the carbon atoms bearing
OH groups are written before the
name of the alcohol.
Alcohols and Ethers
15
2 Give IUPAC names for the following compounds.
a. The chain has four carbons and the
OH group is attached to the second
so it is named 2–butanol (sec–butyl alcohol).
b. The
OH group is in the middle of the chain and the hydrocarbon chain is
unsaturated. Numbering is started at the end nearer to the double bond. The chain has 5 carbons so the parent name is pentene. The double bond is between first and second carbon atoms and the
OH
group is attached to the third carbon atom. So the name of the compound is 1-penten-3-ol.
c. The
OH group is attached to a cyclohexane. Numbering starts from the
carbon atom bearing the
OH group so that the carbon bearing bromine
is given the lower number. The name of compound is 3–bromocyclohexanol.
d. The longest aliphatic carbon chain has 3 carbons. Numbering starts at the end nearest the
OH group.
OH is attached to the first carbon and the
phenyl group is attached to the second carbon atom.
16
Oxygen And Nitrogen Containing Organic Compounds
3 Draw the structural formulae of the following compounds.
a. 1–methylcyclohexanol b. 2,3–dimethyl–2,3–butanediol c. 2,4–dimethyl–1–pentanol d. 4–phenyl–2–pentanol
a. To a cyclohexane molecule a methyl and a hydroxyl group are attached. The structure is
b. Two methyl and two hydroxyl groups are bonded to a hydrocarbon chain with four carbons. Both the 2 nd and 3rd carbon atoms have one methyl and one hydroxyl group attached. The structure is
c. Two methyl and one hydroxyl group are attached to a hydrocarbon chain c ontaining 5 carbons. The 1st carbon atom bears the hydroxyl group, the 2 nd and 4th carbons bear the CH3
groups.
The structure is
d. A hydrocarbon containing 5 carbon atoms has one hydroxyl group on the second carbon and a phenyl group on the fourth carbon. The structure is
3. PHYSICAL PROPERTIES OF ALCOHOLS Alcohol molecules are formed by nonpolar alkyl (R
) and polar hydroxyl (
OH)
groups. These two groups play an important part in determining the physical properties of alcohols.
Alcohols and Ethers
17
The physical properties of alcohols lay somewhere between the physical properties of hydrocarbons and water depending upon the R
and
OH groups that
make up the alcohol molecule. The hydrocarbon properties become more significant as the number of carbon atoms in the molecule increases. Similarities to water become more obvious in smaller molecules. For example, in methanol, the hydroxyl group has a strong influence. Methanol and water are miscible in all proportions. Methanol is polar and similar to water.
a. Hydrogen bonding in alcohol molecules b. Hydrogen bonding in water molecules
The polarity of alcohols decreases as the length of the hydrocarbon chain in the molecule increases. Consequently, their solubilities in water decrease. At room temperature, the solubilities of n-butanol, n-pentanol and n-octanol in 100 ml of water are 8.3 g, 2.4 g and 0.05 g respectively. Branching of alcohols increases solubility. For example, the solubility of n-butyl alcohol is 8.3 g per 100 ml of H 2O but tert-butyl alcohol is completely soluble in water. The polarity of alcohols increases as the number of
OH groups increases.
Ethylene glycol, C2H4(OH)2 and glycerol, C3H5(OH) 3 are soluble in water in any proportion. Also, longer chained alcohols such as 1,4-butandiol, 2,3-butandiol and the three isomers of pentandiol are highly soluble in water. The boiling points of alcohols are much higher than that of their corresponding hydrocarbons since alcohol molecules are polar and undergo hydrogen bonding. For example, methane has a boiling point of –162°C while methanol has a boiling point of 64.7°C. 18
Oxygen And Nitrogen Containing Organic Compounds
a. Like most alcohols, methyl alcohol is polar. Therefore, it is highly soluble in water which is a good polar solvent. b. Like many organic compounds, methane has a nonpolar structure and therefore it is not soluble in water.
The boiling points of alcohols increase with increasing molar mass as van der Waals forces increase with increasing molecular size. At the same time as the boiling point increases volatility decreases. In primary alcohols, increasing the branching in alkyl groups decreases the boiling point. When alcohols branch, the surface contact of molecules decreases and therefore the van der Waals forces decrease. The boiling points of three isomers of primary pentanol are shown below.
Figure1 : Number of carbon atoms in straight chain alcohols versus boiling point
Alcohols and Ethers
19
Alcohol
Formula
Melting
Boiling
Density
Solubility
Point (°C)
Point (°C)
(g/mol)
(g/100 mL water)
Methyl alcohol
CH3OH
– 97
64.7
0.792
Ethyl alcohol
C2H5OH
– 117
78.3
0.789
n – propyl alcohol
CH3CH2CH2OH
– 126
97.2
0.804
Isopropyl alcohol
(CH3)2CHOH
– 88
82.3
0.786
n – butyl alcohol
CH3(CH2)3OH
– 90
117.7
0.810
Isobutyl alcohol
(CH3)2CHCH2OH
– 108
108.0
0.802
10
sec – butyl alcohol
CH3CH2CHOHCH3
– 114
99.5
0.808
26
tert – butyl alcohol
(CH3)3COH
25
82.5
0.789
n – pentyl alcohol
CH3(CH2)4OH
– 78,5
138
0.817
2.30
n – hexyl alcohol
CH3(CH2)5OH
– 52
156.5
0.819
0.60
n – heptyl alcohol
CH3(CH2)6OH
– 34
176
0.822
0.20
n – octyl alcohol
CH3(CH2)7OH
– 15
195
0.825
0.05
n – nonyl alcohol
CH3(CH2)8OH
– 5.5
212
0.827
–
n – decyl alcohol
CH3(CH2)9OH
6
228
0.829
–
24
161.5
0.962
3.60
– 15
205
1.046
4
Cyclohexyl alcohol Benzyl alcohol
C6H5CH2OH
Ethylene glycol
HO(CH2)2OH
– 12.6
197
1.113
Propylene glycol
HO(CH2)3OH
– 59
187
1.040
Glycerol
C3H5(OH)3
18
290
1.261
Allyl alcohol
CH2
– 129
97
0.855
CHCH2OH
Table 1: Physical properties of some alcohols
In a monoalcohol, from the primary to tertiary structure, the boiling point decreases since the branching increases. The boiling points of primary, secondary and tertiary butanols are given below;
20
Oxygen And Nitrogen Containing Organic Compounds
The melting point of alcohols increase as the number of carbon atoms increase. At room temperature the normal alcohols (C 1
C11 ) up to dodecanol
(C12H25OH, m.p. = 24°C) are liquids and the others with carbon numbers greater than 11 are all solids. Branching generally decreases the melting points of alcohols (compare the melting points of n–butyl alcohol and iso–butyl alcohol) although symmetric branching leads to an increase in melting point.
4 Arrange the following compounds in order of decreasing solubility in water. I. CH3 II. CH3 III.
CH2
CH2
(CH2)3
CH2
CH2
OH
IV. HO
CH3
(CH2)3
CH2
OH
The first molecule is an alkane, the others are alcohols. Alkanes are not soluble in water. As a result, the compound CH 3CH2CH2CH3 is the least soluble. Since the fourth compound has two
OH groups, it is more soluble than the
others. Consequently, the order of decreasing solubilities of given compounds in water is: IV > III > II > I
5 Arrange the following compounds in order of decreasing boiling points. I. C2H5OH
II. C3H7OH
III.
IV.
Alcohols and Ethers
21
All the compounds are alcohols. It is known that when the molar mass of alcohols increases the boiling point also increases. The first compound, C 2H5OH (46 g/mol) therefore has the lowest boiling point. The second and fourth compounds are isomers of propanol. As the number of branches increases, the boiling point decreases. The fourth alcohol has more branches than the second one, so it has a lower boiling point. The molar mass of ethylene glycol (3 rd compound) is near to that of propanol. However since it has two –OH groups, it boils at a higher temperature. As a result the boiling point order is III > II > IV > I.
4. CHEMICAL PROPERTIES OF ALCOHOLS
The chemical properties of alcohols are determined by the oxygen atom in the
OH group. This oxygen atom is bonded to a carbon and hydrogen atom by
sigma (single) bonds. The bonds between C
O and O
H are polar. The elec-
tronegativities of oxygen, carbon and hydrogen are 3.5, 2.5 and 2.1 respective
Because of the difference in electroneg ativities between C , O and H alcohols have polar properties.
ly, oxygen having the highest electronegativity. When the polarities of C
O and O
H bonds are compared, it is seen that the
O
H bond is more polar than the C
O bond. The hydrogen atom in the
O
H bond becomes partially positively charged and therefore in some reac-
tions, alcohols can act as proton (H +) donors. From primary alcohols to tertiary alcohols the polarity and therefore the proton donating ability of the
O
H
bond decreases.
4.1. REACTIONS OF ALCOHOL INVOLVING O — H BOND BREAKAGE Pure alcohols can undergo self-ionization in the same way as water but the ionization of pure alcohols is less than that of water. During the ionization, an alcohol molecule is converted into an alkoxide (RO –) ion by when it loses a proton, the molecule accepting the proton is converted into an oxonium ion.
22
Oxygen And Nitrogen Containing Organic Compounds
The ionization percentage of alcohols decreases as the number of carbon atoms increases. In reactions with alcohols involving O (H+)
H bond breakage, protons
are donated.
Reactions of Alcohols with Alkali Metals Alcohols display the properties of weak acids. The reactions of alcohols with active metals (such as Na and K) are slower than the equivalent reactions with water. During these reactions, basic salts of the alkoxide ion (RO
) are pro-
duced.
Potassium reacts with water and produces potassium hydroxide and hydro gen.
Methanol and ethanol react strongly with Na and K. When the carbon chain of the alcohol extends the intensity of the reaction decreases. Generally, potassium is preferred for the long-chained alcohol reactions. Some metals, such as magnesium and aluminum can react with alcohols to produce H 2 gas when their oxide layers are cleaned from their surfaces.
The rate of reaction of alcohols with alkali metals decreases from primary alcohols to tertiary alcohols. Basic alkoxides react with water (hydrolyze) to produce their initial alcohols.
Ethanol reacts with sodium and produces sodium ethoxide and hydrogen. When sodium is put into ethanol, it settles down and reacts slowly.
The activity order of some molecules (containing the –OH group) with Na and K metals Alcohols and Ethers
23
6 40 grams of 92% pure (by mass) ethyl alcohol reacts with an excess amount of potassium metal. How many liters of H 2 gas are produced at the end of the reaction at STP (impurities in the mixture do not react with potassium). (C2H5OH : 46 g/mol)
Let’s calculate the number of moles of ethyl alcohol. Firstly the mass of pure ethyl alcohol is calculated. mC
2H5OH
92 = 40 g · ––––– = 36.8 g 100
The number of moles of ethyl alcohol is found. nC
2H5OH
m 36.8 g = ––––– = ––––––––––– = 0.8 mol M 46 g/mol
The reaction between ethyl alcohol and potassium is 2C2H5OH + 2K
2C2H5OK + H2
We can find the mole number of hydrogen from the mole number of the alcohol by proportion: 2 mol C2H5OH
1 mol H2
0.8 mol x —————————————————— nH = x = 0.4 mol 2
So the volume of hydrogen at STP is: V H = 0.4 · 22.4 = 8.96 L. 2
7 When 20 grams of an ethane - ethanol mixture is reacted with an excess amount of Na metal, 2.8 L of H 2 gas is produced at STP. What was the mass percentage of ethyl alcohol in the original mixture? (C2H5OH : 46 g/mol)
The collection of H 2 gas over water produced from the reaction of ethanol with sodium can easily be observed. 24
Since ethane is a paraffin, it does not react with sodium. The reaction of ethyl alcohol with sodium is 2C2H5OH + 2Na 2C2H5ONa + H 2
Oxygen And Nitrogen Containing Organic Compounds
The mole number of hydrogen produced is: 2.8 L nH2 = ––––––––––––– = 0.125 mol 22.4 L/mol The mole number of ethanol is twice the mole number of hydrogen so: nC
2H5OH
= 2 . nH = 2 . 0.125 = 0.25 mol 2
Then the mass of ethanol is mC2H5OH = n . M 0.25 mol . 46 g/mol = 11.5 g Since the mixture is 20 grams, the percentage of alcohol is Ethyl alcohol % = (11.5 g / 20 g) . 100 = 57.5
Esterification Reactions From the reaction between alcohols and carboxylic acids, esters and water are produced. This is called esterification. In this reaction, the hydrogen atom from the
OH group of an alcohol is replaced by the acyl group from a carboxylic
acid. These reactions occur in the presence of strong acid catalysts such as HCl or H2SO4.
Inorganic acids also react with alcohols to form esters. In these esterification reactions, as well as HNO 3, H 2SO4 and H3PO4 , inorganic acid halides such as SOCl2, and PCl 3 can be used.
Alcohols and Ethers
25
8 1 mole of acetic acid (CH 3COOH) reacts with 1 mole of a monohydric alcohol to produce an ester with a molar mass of 102 g/mol. What is the molecular formula of the alcohol used in the reaction? CH3COOH : 60 g/mol, H2O : 18 g/mol H : 1 g/mol C : 12 g/mol O : 16 g/mol
In esterification reactions, 1 mol of carboxylic acid reacts with 1 mol of monohydric alcohol to produce 1 mol of ester and 1 mol water. Carboxylic acid + Monohydric alcohol Ester + Water. Since total mass is conserved in a chemical reaction, the sum of the mass of alcohol and acid should be equal to sum of the mass of ester and water. macid + malcohol = mester + m water 60 + malcohol = 102 + 18 malcohol = 60 gram So 1 mol of monohydric alcohol is 60 gram. Since the general formula of monohydric alcohols is C nH2n+1OH, the following calculation can be done. MC
nH2n+1OH
= 60 g/mole
12n + (2n + 1) . 1 + 16 + 1 = 60 14n = 42 n=3 We can write the molecular formula as C 3H7OH, propyl alcohol.
9 When a 115 gram sample of impure ethyl alcohol (C 2H5OH) is reacted with an excess amount of acetic acid (CH 3COOH), 176 grams of ester is obtained. What is the mass percentage of pure alcohol in the sample? (C2H5OH : 46 g/mol, CH3COOH : 60 g/mol) 26
Oxygen And Nitrogen Containing Organic Compounds
The esterification reaction of ethyl alcohol:
The molar mass of the ester: MC
4H8O2
= (4 . 12) + (8 . 1) + (2 . 16) = 88 g/mol
The number of moles of ester m 176 g nC H O = ––––– = –––––––––––– = 2 mol 4 8 2 M 88 g/mol According to the reaction, the number of moles of alcohol is equal t o the number of moles of ester; nC
2H5OH
= nC
4H8O2
= 2 mol
Then the mass of the alcohol is mC
2H5OH
= M . n = 46 g/mol . 2 mol = 92 g
Finally we can find the mass percentage of pure alcohol in the sample. in 115 g sample in 100 g sample
92 g is ethyl alcohol x g
—————————————————————————————
92 . 100 x = ————— = 80% 115
4.2. REACTIONS OF ALCOHOLS INVOLVING C — O BOND BREAKAGE In alcohols it is seen that the
electrons.
structure has two pairs of nonbonded
These electrons cause alcohols to be protonated (accept protons) in acid solutions. In these type of reactions alcohols act as base. During the reaction the oxonium ion
is produced.
If this ion encounters a strong electrophile (a species attracted to electrons), a water molecule is removed from the ion as a result of C
O bond breakage. Alcohols and Ethers
27
Electrophilic atoms or atom groups bond to carbon in the
structure.
These type of reactions are explained below.
Reactions of Alcohols with Hydrogen Halides Alcohols react with hydrogen halides to produce alkyl halides. In these reactions, Activity order of HX : HI > HBr > HCI
the
OH group of the alcohol is replaced by the halide ion of the acid. All alco-
hols react with concentrated HBr and HI solutions to produce alkyl bromide and alkyl iodide. These reactions occur by a specific mechanism as shown below.
RX + H2O (X : Br, I)
ROH + HX
C2H5OH + HI C2H5I + H 2O Concentrated HCl solution reacts with tertiary alcohols directly but only reacts with primary and secondary alcohols in the presence of a ZnCl 2 catalyst. A solution of ZnCl 2 salt in HCl is known as “Lucas reagent”. R
ZnCl2
OH + HCl
CH2
(CH3)3C
CH2
25°
OH + HCl (CH3)3C ZnCl2
CH2
ZnCl2
OH + HCl CH3 heat
Cl + H2O
Cl + H2O
OH + HCl (CH3)2CH
(CH3)2CH CH3
R
Cl + H2O
CH2
Cl + H2O
The Reactions of Alcohols with Acid Halides
The reactions of alcohols with acid halides occur in two steps. In the first step, lone pairs of electrons on the oxygen atoms in alcohol molecules attract proton (H +) from the acid to form the oxonium ion. In the second step, the bond between the alkyl group (R –) and oxygen atom weakens and is then broken. Oxygen takes the bonding electrons, thus the R – group becomes positively charged. The negatively charged ion of the acid halide bonds to the positively charged alkyl group (R +–) to form the R – X compound.
28
Oxygen And Nitrogen Containing Organic Compounds
10 Write the equations for the reactions between the following substances.
a. 2–propanol + Lucas reagent b. 2–methyl–2–butanol + HCl
a. Since 2–propanol compound is a secondary alcohol, it reacts with Lucas reagent to form isopropyl chloride.
b. 2–methyl–2–butanol is a tertiary alcohol. Therefore it reacts with HCl at 25°C readily. In the reaction, the
OH group of the second carbon of the alcohol
is replaced by the Cl atom from HCl and tert-butyl chloride is formed.
Dehydration of Alcohols 1. When one mole of monohydric alcohol is heated in the presence of a concentrated H2SO4 catalyst at high temperature, one mole of water and one mole of alkene is produced. To undergo this reaction, the carbon adjacent to the carbon with the R
CH2
CH3
OH group needs a H atom bonded to it. H2SO4
OH R
CH2
CH2
180 °C
CH2
CH
H2SO4
OH CH3 180 °C
CH2 + H2O CH
CH2 + H2O
The reaction follows Markovnikov’s rule.
2. At a lower temperature, a simple ether can be produced from the dehydration of two moles of monohydric alcohols.
Alcohols and Ethers
29
11 Write the equations for the following reactions.
a. Dehydration of n – butanol in the presence of a H2SO4 catalyst at 180 °C. b. Dehydration of isopropanol in the presence of a H 2SO4 catalyst at 140 °C.
a. When 1 mol of n-butanol is heated up to 180 °C, an alkene and 1 mol water are produced. CH3
CH2
CH2
CH2
OH
H2SO4
n–butanol
180°C
CH3
CH2
CH
CH2 + H 2O
n–butene
b. 2 mol isopropanol can produce 1 mol water when heated up to 140 °C in the presence of a H2SO4 catalyst. In this reaction the OH group of an alcohol and the H from the OH group of other alcohol join together to form water. The remaining alcohol fragments bond to each other. As a result, isopropyl ether is formed.
12 A sample of 50 gram of 92% pure ethyl alcohol is used to produce ethylene with an 80% yield,
a. How many grams of alkene can be obtained? b. How many grams of ether can be obtained? (C2H5OH : 46 g/mol, C4H10O : 74 g/mol) 30
Oxygen And Nitrogen Containing Organic Compounds
a. The amount of pure alcohol is
92 50 g . ——— = 46 g 100
46 g the number of moles of ethyl alcohol is; n = ————— = 1 mol. 46 g/mol From the dehydration of 1 mol ethyl alcohol, 1 mol ethylene is obtained. H2SO4
C2H5OH C2H4 + H2O 180 °C
1 mol
1 mol
1 mol
The molar mass of ethylene is = 2 . 12 + 4 . 1 = 28 g/mol. m C2H4 = 28 g But the reaction has an 80% yield. So the mass of ethylene produced is 80 mC2H4 = 28 . ——— = 22.4 g 100
b. As can be seen in the given equation, at 140 °C with the help of H2SO4 , from the dehydration of 2 moles of ethyl alcohol 1 mole of ether is obtained. 2C2H5OH C2H5
O
C2H5 + H2O
If 1 mole C2H5OH is used at the beginning of the reaction, 2 mol of alcohol
1 mol of ether
1 mol of alcohol x mol of ether ———————————————————— x = 0.5 mol of ether is obtained at the end. Then the mass of ether is calculated. m m n = —— 0.5 = —— m = 37 g M 74 But the reaction has only an 80% yield. So the mass of ether produced is; MC
4H10O
80 = 37 . ——— = 29.6 g ether 100
4.3. OXIDATION OF ALCOHOLS To oxidise alcohols, acidic solutions of strong oxidising agents, such as KMnO 4, K2Cr2O7 or K2CrO4 are used. The degree of oxidation of alcohols depends on the number of H atoms bonded to the carbon atom bearing the
OH group.
Alcohols and Ethers
31
Oxidation of Primary Alcohols In primary alcohols, the carbon atom bearing the
OH group has two hydro-
gen atoms, except methanol, which has three. Therefore, primary alcohols can be oxidised two degrees. In the first oxidation, an aldehyde is produced, in the second oxidation, a carboxylic acid is produced.
The notation [O] above the arrows in the reaction equations indicates oxida-
tion by the addition of oxygen from an oxidant.
Let’s examine the oxidation of ethyl alcohol.
Oxidation of Secondary Alcohols In secondary alcohols, there is only one hydrogen atom on the carbon atom bearing the
OH group. Therefore, secondary alcohols can be oxidised by only
one degree. The end product of the oxidation is a ketone.
Oxidation of Tertiary Alcohols Tertiary alcohols can not be oxidised because they do not have a hydrogen atom on the carbon atom bearing the
32
Oxygen And Nitrogen Containing Organic Compounds
OH group.
However, if tertiary alcohols are heated up to very high temperatures in the presence of a catalyst, they can decompose into unsaturated hydrocarbons and water.
13 Write out the following reactions.
a. Oxidation of methanol by K 2Cr2O7 in H2SO4 solution. b. Oxidation of 2-propanol by KMnO 4 in H2SO4 solution.
a. Oxidation of methanol (CH 3OH) occurs in three steps, as methanol has 3 H atoms directly bonded to C atom. In the first step, methanol oxidises to an aldehyde (methanal). 3CH3O H + K2Cr2O7 + 4H2SO4 3HCHO + K2SO4 + Cr2(SO4)3 + 7H2O In the second step, the formed aldehyde oxidises to carboxylic acid (methanoic acid) 3HCHO + K2Cr2O7 + 4H2SO4 3HCOOH + K2SO4 + Cr2(SO4)3 + 4H2O In the third step oxidation produces carbonic acid from carboxylic acid which is unstable and decomposes to CO 2 and H2O. 3HCOOH + K2Cr2O7 + 4H2SO4 3H2CO3 + K2SO4 + Cr2(SO4)3 + 4H2O H2CO3
CO2 + H2O
b. 2–propanol is a secondary alcohol. So it is fully oxidised in only one step. The product will be a ketone (2–propanone)
Alcohols and Ethers
33
14 The molar mass of an aldehyde which is produced by the one degree oxidation of a monohydric alcohol is 46 g/mol. Calculate the molar mass of the alcohol used in this reaction.
According to the reaction, 1 mol of an alcohol can produce 1 mol of an aldehyde. Two hydrogen atoms from the alcohol are used in the formation of water. Therefore the molar mass of the aldehyde produced is 2 g/mol less than that of the alcohol. Molar mass of aldehyde = x – 2 = 46 g/mol Molar mass of alcohol, x = 48 g/mol
15 A 10 grams mixture of 2 - methyl - 2 - propanol and 2 - butanol is reacted with excess K2Cr2O7 in acidic solution. At the end of the reaction 3.6 grams of ketone is obtained. Find the percentage of 2 – butanol in the original mixture.
2 - methyl - 2 - propanol is a tertiary alcohol; 2 - butanol is a secondary alcohol. Secondary alcohols are oxidised to ketones but tertiary alcohols do not undergo oxidation.
34
Oxygen And Nitrogen Containing Organic Compounds
A ketone (methyl ethyl ketone) is produced by the oxidation of 2 - butanol. The molar mass of the ketone is: MC
= (4 . C) + (8 . H) + O
MC
= (4 . 12) + (8 . 1) + 16 = 72 g/mol
4H8O 4H8O
m 3.6 g n = —— = ————— = 0.05 mol M 72 g/mol According to the balanced equation given above, 3 mol of butanol produces
3 mol of methyl ethyl ketone
x mol of butanol produces 0.05 mol of methyl ethyl ketone —————————————————————————————— x = 0.05 mol M of 2 - butanol is M C
4H10O
mC
4H10O
= (4 . C) + (10 . H) + (1 . O) = 74 g/mol
= n . M = 0.05 . 74 = 3.7 gram
10 g mixture has
3.7 g of 2 - butanol
100 g mixture has x g ———————————————————————— x = 37 g the percentage of 2 - butanol is 37% in the original mixture.
4.4. COMBUSTION REACTIONS OF ALCOHOLS Alcohols, like hydrocarbons, burn in excess oxygen to form CO 2 and H2O. Combustion reactions of monohydric, dihydric and trihydric alcohols are given below.
Monohydric alcohol: 3n CnH2n+1 (OH) + —— O2 n CO2 + (n + 1)H 2O 2 C3H7OH + 9/2O2 3 CO2 + 4H2O
Dihydric alcohol: 3n–1 CnH2n (OH)2 + ——— O2 nCO2 + (n + 1)H 2O 2 C2H4(OH)2 + 5/2O2 2CO2 + 3H2O
Trihydric alcohol: 3n–2 CnH2n – 1 (OH)3 + ——— O2 nCO2 + (n + 1)H 2O 2 C4H7(OH)3 + 5O2 4CO2 + 5H2O Alcohols and Ethers
35
16 When 0.25 mol of a monohydric alcohol is burned, 16.8 L of CO 2 gas is produced at STP. What is the molecular formula of the alcohol?
Combustion of monohydric alcohols: 3n CnH2n+1OH + ——— O 2 nCO2 + (n+1)H2O 2 16.8 L nCO = ——————— = 0.75 mol 2 22.4 L/mol If 0.25 mol of alcohol is burned
0.75 of mol CO 2 is produced
If 1 mol of alcohol is burned n mol of CO 2 is produced ————————————————————————————————— n = 3 mol If we substitute n = 3 into the general formula, CnH2n+1OH; the molecular formula will be C3H7OH.
5. PREPARATION OF ALCOHOLS 5.1. SYNTHESIS OF ALCOHOLS FROM ALKENES Alcohols can be prepared by the acid catalysed addition of water to alkenes. Concentrated H2SO4 is used as catalyst. The addition follows Markovnikov’s rule. Secondary and tertiary alcohols can be produced by this method, but primary alcohols cannot (except for ethanol).
This reaction is reversible and the mechanism for the hydration of an alkene is simply the reverse of that of the dehydration of an alcohol. 36
Oxygen And Nitrogen Containing Organic Compounds
5.2. SYNTHESIS OF ALCOHOLS FROM ALKYL HALIDES Hydration of alkyl halides by alkaline hydroxides produces alcohols. In this reac-
Alkaline hydroxides are bases that are
tion the halogen atom is replaced by the
soluble in water. Hydroxides of all group
R
X
+
alkyl halide
CH3CH2
OH group to form an alcohol.
NaOH
R
alkaline hydroxide
CI
+
ethyl chloride
OH
+
NaX
alcohol
NaOH
alkaline halide
CH3CH2
sodium hydroxide
OH
+
1A metals and calcium, strontium and barium from group 2A are alkaline.
NaCl
ethyl alcohol
sodium chloride
5.3. SYNTHESIS OF ALCOHOLS BY THE REDUCTION OF ALDEHYDES, KETONES AND CARBOXYLIC ACIDS Alcohols can be obtained by reacting of aldehydes, ketones or carboxylic acids with hydrogen gas in the presence of a platinum (Pt) catalyst. As a result of the reduction of aldehydes by one degree and carboxylic acids by two degrees primary alcohols are obtained. Reduction of ketones by one degree produces secondary alcohols.
5.4. SYNTHESIS OF ALCOHOLS USING GRIGNARD REAGENTS Grignard reagents, alkyl magnesium halides (R – Mg – X), react with aldehydes and ketones. Alcohols and Ethers
37
The Grignard reagent reduces these compounds, which contain the
carbonyl group,
to alcohols.
I. If a primary alcohol is desired, the reaction should be initiated with formaldehyde. By this way, an alcohol, containing at least two carbons, is produced.
II. If a secondary alcohol is desired, Grignard reagents should be reacted with an aldehyde other than formaldehyde.
III. If a tertiary alcohol is desired the Grignard reagent should be reacted with a ketone.
17 Give the required reactants needed to produce the following compounds using Grignard reagents and write down the chemical equations.
a. 1-butanol b. 2-butanol c. 2-methyl-2-propanol 38
Oxygen And Nitrogen Containing Organic Compounds
a. 1-butanol is a primary alcohol. To produce it, the reaction should be started with formaldehyde and a Grignard reagent. Since formaldehyde has one carbon atom and butanol has four carbon atoms, the Grignard reagent should have three carbon atoms.
b. 2-butanol is a secondary alcohol. To produce it, the Grignard reagent should react with an aldehyde other than formaldehyde. Since the hydroxyl group is attached to the second carbon of 2 - butanol, the aldehyde should have two carbon atoms and the Grignard reagent should also have 2 carbon atoms.
c. 2-methyl-2-propanol is a tertiary alcohol and contains 4 carbon atoms. To produce it, a Grignard reagent should be treated with a ketone. The ketone needs 3 carbons and the Grignard reagent needs 1 carbon so the total number of carbons will be equal to 4.
6. SOME IMPORTANT ALCOHOLS 6.1. METHYL ALCOHOL (METHANOL) Physical Properties Methyl alcohol is colorless, flammable and has a characteristic odor. Its taste is similar to ethanol but it is highly toxic. Ingestion of even small quantities of methyl alcohol can cause blindness, large quantities cause death. Methyl alcohol poisoning may also occur by inhalation of the vapors or by prolonged exposure to the skin. Since methyl alcohol can be deadly, pyridin, which has a bad odor, or dyes are added to it to prevent its use as a drink. As methyl alcohol has a low freezing point (–97 °C), it has been used as antifreeze in radiators.
To distinguish between ethanol and methyl alcohol the borax test is used. When boric acid reacts with methanol, a pale green flame is observed. Alcohols and Ethers
39
Addition of 5–30 % methyl alcohol to
However, its boiling point (64.7 °C) is lower than that of water, and so usage of
gasoline decreases polluting particles
methyl alcohol has decreased in this area. Methyl alcohol can be dissolved in all
produce d from car exhausts. Methyl
proportions in water and organic solvents and can also dissolve fats and resins.
alcohol can be produced from sub-
Methyl alcohol can be converted into formaldehyde and this is the raw material
stances other than petroleum. The most important and the cheapest being coal. It can also be produced from wood, agricultural remnants and dumps.
for industrial products such as plastics, paints and solvents.
Chemical Properties Methyl alcohol is the most active and the most acidic member of the monohydric alcohols. CH3OH + H2O
CH3O– + H3O+
It displays all the properties of alcohols. It is easily flammable and burns with a bluish flame. Methyl alcohol can be easily oxidised. It turns into formaldehyde in the first degree of oxidation, into formic acid in the second and carbon dioxide in the third. CH3
[O]
–H2O
methyl alcohol
In some countries, methyl alcohol is used as fuel. Compared with gasoline, methyl alcohol causes more wear to the engine, this is a disadvantage of methyl alcohol.
[O]
[O]
OH HCHO HCOOH H2CO3 CO2 + H2O formaldehyde
formic acid
–H2O
carbonic acid
carbon dioxide
18 Write the reactions of methyl alcohol with
a. Sodium,
b. Acetic acid,
c. Acid halides
a. CH3OH + Na CH3ONa + 1/2H2 b. CH3OH + CH3COOH CH3COOCH3 + H2O c. CH3OH + HX CH3 X + H 2O
19 How many grams of formaldehyde must be used to produce 80 grams of methyl alcohol in a reaction with a 75% yield? (C : 12 g/mol, H : 1 g/mol, O : 16 g/mol)
M of methyl alcohol: M CH 40
3OH
= 12 + (4 . 1) + 16 = 32 g/mol
Oxygen And Nitrogen Containing Organic Compounds
m 80 g n = ——— = —————— = 2.5 mol M 32 g/mol Reduction of formaldehyde by one degree produces methyl alcohol.
According to the equation 1 mole of methyl alcohol is produced by 1 mole of formaldehyde. To produce 2.5 moles of methyl alcohol, 2.5 moles of formaldehyde must be used. MHCHO = 12 + 2 + 16 = 30 g/mol m = n . M = 2.5 . 30 = 75 g The reaction occurs with a 75% yield. for 75% yield
75 g formaldehyde is used
if 100% yield x g ——————————————————————————— x = 100 g
Synthesis Methyl alcohol is the simplest member of the alcohols and is also known as methyl alcohol or wood alcohol. It was originally produced from the distillation of wood at high temperature in the absence of air, hence it is known as wood alcohol or wood spirit. While heating, wood which is composed of cellulose, decomposes into simpler compounds. Some of these compounds are acetone, acetic acid and methyl alcohol. The mixture obtained is passed through cold water to condense it. Up until 1925, this method was used to synthesize methyl alcohol. In 1920 however, methyl alcohol was produced more cheaply using a new method discovered Germany. Here, methyl alcohol was produced by the more reaction of CO and H2 gases under high pressure and temperature in the presence of a catalyst. Today, most methyl alcohol is prepared by this method. ZnO – Cr2O3
CO + 2H 2 300 – 400°C/200 atm
History Ethyl alcohol has been known to
CH3OH
H = –90.5 kJ/mol
6.2. ETHYL ALCOHOL
humankind since prehistory as the active ingredient of alcoholic beverages. Its isolation as a relatively pure compound was probably achieved first
Physical Properties
by Islamic alchemists who developed
Pure ethyl alcohol is colorless and has a characteristic smell. It is miscible with
the art of distillation, such as Al–Geber
water and is toxic, affecting the central nervous system.
(721–815) and Al–Razi (864–930).
It freezes at –114 °C, boils at 78.3 °C and has a density of 0.789 g/mL
Alcohols and Ethers
41
Chemical Properties The ethyl alcohol that is used as a solvent in laboratories is composed of 95% ethyl alcohol and 5% water. This mixture is called common ethyl alcohol. Such a mixture is an example of an azeotropic mixture and boils at 78.15°C. 100% pure ethyl alcohol is known as absolute alcohol or absolute ethyl alcohol. Pure ethyl alcohol can be prepared by adding lime (CaO) to common ethanol. Using this method, H 2O is precipitated as Ca(OH) 2. CaO + H 2O Ca(OH) 2 Spirit is a derivative of ethyl alcohol, used as fuel in cookers.
In industry, another method to prepare pure ethanol is to add benzene to the mixture of 95% ethanol and water. Benzene forms a different azeotrope with ethanol and water. This azeotrope boils at 64.9°C and allows for the distillation of pure ethanol.
To prevent the drinking of ethyl alcohol, which is used as a fuel, pyridine, which has a bad odor and dyes are used. This mixture is known as spirit.
Ethyl alcohol is an important organic solvent. It is used in the preparation of tincture of iodine, paints, essences, perfumes and cosmetics. It is also found in drinks, spirit and cologne. Ethyl alcohol is the starting substance for most organic compounds. Burning of ethyl alcohol reaction given as follow C2H5OH + 3O2 2CO2 + 3H2O + 1374 kJ Ethyl alcohol can burn very well therefore it can be used in internal combustion engines. Ethyl alcohol is used in antifreeze products, and also as a fuel a solution of 70–85% of ethyl alcohol is commonly used as a disinfectant. It kills organisms by denaturing their proteins and dissolving their liquids and it is effective against most bacteria, fungi and many viruses though ineffective against bacterial spores. Ethyl alcohol which is taken into the body via alcoholic beverages slowly causes permanent, harmful effects. Alcohol copies water molecules and takes their place in the brain, causing changes in the nervous system.
Synthesis To synthesize ethyl alcohol, many methods may be used. Some of these methods are; Ethyl alcohol produced by the fermentation process is purified by fractional distillation.
1. By Fermentation Most ethanol is prepared by the fermentation of sugar. It can be fermented by;
a. Plants containing starch: Wheat, corn, potato, oats, etc. b. Plants containing sugar: Sugarbeet, sugarcane and fruits. 42
Oxygen And Nitrogen Containing Organic Compounds
In the fermentation process, carbohydrates in these sources are converted into simple sugars (glucose and fructose) and then these are converted into alcohol and carbon dioxide. maltase
2C6H12O6
C12H22O11 + H 2O maltose
C6H12O6
glucose zymase
2C2H5OH + 2CO2
glucose
ethyl alcohol
Yeast is added to glucose solution and it is allowed to ferment. CO 2 gas pro-
2. From Ethene Ethyl alcohol for industrial purposes is produced by hydrating ethene using a phosphoric acid catalyst. This process costs less than fermentation.
duced by fermentation clouds the Ca(OH)2 solution in the test tube.
300°C
C2H4(g) + H 2O(g) C2H5OH(l) pressure
ethene
ethyl alcohol
3. By Acetaldehyde
When ethyl alcohol is burned in a porcelain cup, a pale yellow flame is observed.
20 Complete the following reactions.
H2SO4
a. Ethyl alcohol + potassium
d. Ethyl alcohol
b. Ethyl alcohol + acetic acid
e. Ethyl alcohol + hydrogen iodide
c. Ethyl alcohol
H2SO4
180 °C
140 °C
[O]
[O]
f. Ethyl alcohol .......... Alcohols and Ethers
43
a. C2H5OH + K C2H5OK +1/2 H2 H+
b. C2H5OH + CH3COOH CH3COOC2H5 + H2O H2SO4
c. C2H5OH C2H4 + H2O 180 °C
H2SO4
d. 2C2H5 OH C2H5 140 °C
O
C2H5 + H2O
e. C2H5OH + HI C2H5I + H 2O [O]
f. C2H5OH CH3 –H2O
[O]
CHO CH3
COOH
21 How many grams of ethyl alcohol can be prepared from 200 grams of 80% pure calcium carbide by a 75% yield reaction? (CaC2 : 64 g/mol, C2H5OH : 46 g/mol)
CaC2 + 2H2O Ca(OH)2 + C2H2 C2H2 + H2O CH3CHO CH3CHO + H2 CH3
CH2
OH
If the equations are added together CaC2 + 3H2O + H 2 CH3
CH2
OH + Ca(OH) 2
is obtained. mass of CaC 2 = 200 . 0.80 = 160 g 160 g number of moles of CaC2 = n = ————— = 2.5 mol 64 g/mol According to the equation, 1 mole of CaC 2 produces 1 mole of ethyl alcohol. It means that from 2.5 mol of CaC2, 2.5 mole ethyl alcohol can be produced. Mass of ethyl alcohol : m = n . M = 2.5 . 46 g/mol = 115 g It is known that the reaction has a 75% yield. So, 115 g ethyl alcohol
100% yield
x g 75% yield ———————————————————— x = 86.25 In this process 86.25 g ethyl alcohol can be produced. 44
Oxygen And Nitrogen Containing Organic Compounds
6.3. GLYCOL Alcohols containing two
OH groups are called glycols. The most important
example is ethylene glycol, C2H4(OH)2. The IUPAC name of ethylene glycol is 1,2 – ethanediol. Ethylene glycol is a colorless, odorless, syrupy liquid. It is completely miscible with water. Since it has a low freezing point it is used as antifreeze in automobiles. A high boiling point (197 °C) and heat of vaporization also makes it useful for this purpose. It is also used in hydraulic brake fluid in cars and as a paint, oil, ink and resin solvent. Ethylene glycol is a primary dihydric alcohol. It produces oxalic acid and various side-products when it is oxidised.
Glycol has a freezing point of –115 °C and is used in automobile radiators as antifreeze.
Glycols can be prepared by the reaction of ethylene dichloride and water;
Alfred Bernhard Nobel
(1843 – 1896)
22 A member of the dialcohols reacts with excess sodium metal to produce 37 grams of an alkoxide and 5.6 L of H 2 gas at STP. Find the molecular formula of the alco-
Alfred Nobel was born in 1833 in Stockholm, Sweden. His family was descended from Olof Rudbeck, the best-known technical genius from Sweden's 17th century era when it was a great power in northern Europe.
hol used.
Nobel invented dynamite in 1866 and later built up companies and laboratories in more than 20 countries all over the world.
The general reaction of dialcohols with Na metal:
On November 27, 1895, Nobel signed his last will providing for the establishment of the Nobel Prize. He died of a cerebral haemorrhage in his home in San Remo, Italy on December 10, 1896.
CnH2n+2O2 + 2Na CnH2n(ONa)2 + H2 5.6 L nH = —————— = 0.25 mol of H 2 gas is produced. 2 22.4 L/mol
Alcohols and Ethers
45
According to the equation 1 mol H2 is produced with 1 mol alkoxide compound. So the number of moles of alkoxide is 0.25 mol. m 37 M of alkoxide is = —— = ——— = 148 g/mol n 0.25 CnH2n(ONa)2 = 148 g/mol 12n + (2n . 1) + (16 + 23) . 2 = 148 n=5 The alkoxide compound has 5 carbon atoms. The general formula of a dialcohol is CnH2n+2O2 So the formula is C5H12O2.
LIFE IN THE POLES
Antifreeze is a liquid cooling agent used in gasoline and diesel engines. Compounds are added to the water to reduce the freezing point of the mixture. In the bodies of polar animals, some chemicals behave as an antifreeze. The cold seas of the polar regions have water temperatures below freezing point. For example, in the Antarctic seas, the water temperature is between –1 °C to –4 °C. The water temperature varies very little and without adaptation, fish would freeze to death because of the high water content of blood and flesh. Also, all terrestrial insects are cold–blooded animals. That means their body temperature changes with changes in the envi ronment. If the outside temperature decreases to –20 °C, their body temperature also decreases to this same temperature. At this temperature insects normally cannot survive, though an exception to this is an insect species living in the North Pole. These insects protect themselves from the freezing cold by secreting a kind of antifreeze glycerol. Polar animals produce sorbitol or glycerol in their body when the weather gets colder and decrease the amount of water in their body. A polar insect can survive at –87 °C by using its antifreeze.
46
Oxygen And Nitrogen Containing Organic Compounds
6.4. GLYCERINE Glycerine is the simplest trihydric alcohol, also known as glycerol. The IUPAC name of glycerine
Molecular model of glycerine
is 1, 2, 3–propanetriol. Glycerine freezes at 18 °C, boils at 290 °C and has a density of 1.261 g/ml. Glycerine mixes with water, methanol and ethanol in all proportions. It is a nonpoisonous, syrupy liquid and it absorbs moisture well. Glycerine is obtained as a co-product from the hydrolysis of vegetable oils or animal fats. From the esterification of glycerine with nitric acid, the inorganic trinitrate ester (trinitroglycerine) is produced.
Glycerine reacts with potassium permanganate.
This reaction is exothermic. The reaction mixture is cooled by stirring and passing an air current though it as this product (trinitroglycerine) explodes when it is struck or heated to 45 °C. Dynamite is obtained when trinitroglycerine is absorbed by sawdust and kieselguhr (a sand-like substance with tiny pores). It is a useful explosive and is an invention of Alfred Nobel, a Swedish scientist. Glycerine is used as a moisturizing substance in tobacco, shaving and toilet soaps, cosmetics and lotions, and in the manufacture of plastics, cellophane, water colors, printing-press ink, ointment, antifreeze and dynamite. Glycerine can be prepared by any of the general methods for preparing alcohols but this is not economic. Cheap glycerine is obtained when fats and oils are hydrolyzed in a basic medium or by the fermentation of sugars.
Trinitroglycerine is used in making dyna mite.
7. INTRODUCTION TO ETHERS An ether can be considered as an alcohol derivative resulting from the condensation of alcohols.
Alcohols and Ethers
47
Ethers having the same R groups bonded to oxygen are called simple or symmetric ethers, with different R groups present, they are known as asymmetric or complex ethers. H3C
O
CH3
CH3
simple (symmetric) ether
ethylene oxide
The (R
O
C2H5
complex (asymmetric) ether
) groups in an ether molecule may be alkyl, alkenyl, alkynyl or aryl
groups. tetrahydrofurane
CH3
Ethers may have a cyclic structure, such as ethylene oxide and tetrahydrofurane. Ethylene oxide is a gas at room temper ature and is used as a disinfectant for foods and a fungicide in agriculture.
CH2
O
CH3
H3C
O
ethyl methyl ether
CH2
CH
CH2
allyl methyl ether
methyl phenyl ether
The general formula of ethers is C nH2n+2O and so they are isomers of monohydric alcohols with the same number of carbon atoms. Since there have to be at least two carbons in an ether, there is no isomer of methanol which contains only one carbon.
23 Write the molecular formula of the ethers which are isomers of the following alcohols.
a. The isomer of a monohydric alcohol with two carbon atoms is dimethyl ether which also has two carbons. The molecular formula of dimethyl ether is, CH3
b. CH2
O CH
CH3 O
CH3
c. In benzyl alcohol, there is a benzene ring and a carbon atom. Therefore, a benzene ring and an alkyl group with one carbon atom must be found in t he isomer of benzyl alcohol. It is methyl phenyl ether. The molecular formula is
48
Oxygen And Nitrogen Containing Organic Compounds
8. NOMENCLATURE OF ETHERS 8.1. COMMON NAMES When we name ethers we note to the functional groups attached to the oxygen atom. After naming these groups in alphabetical order we add the word “ether”. If the groups are s ymmetric in the ether, the prefix, di–, is written before the name of the group.
24 Write the common names of the following ethers.
a. Ethyl isopropyl ether
b. Divinyl ether
c. Tert-butyl methyl ether
d. Ethyl phenyl ether
e. Ethyl vinyl ether
f. Tert-butyl phenyl ether
Alcohols and Ethers
49
8.2. IUPAC SYSTEM Ethers are named according to the “alkoxy alkane” (RO –
R+) form in system-
atic naming. The number of the carbon atom to which the alkoxy group (RO –) is attached is indicated.
25 Give the IUPAC name for the following compounds.
a. 2 - phenoxypropane b. 2 - methoxy - 2 - methylpropane c. 1 - methoxy - 3 - bromobenzene d. 2 - methoxypropene e. 2 - methoxypropane f. 1 - ethoxy - 2,4 - dichlorobenzene g. Ethoxyethylene
9. PHYSICAL PROPERTIES OF ETHERS Since the bond angle, R
O
R, is not equal to 180 °C in ethers, they show
limited polarity. Increasing the size of the R ethers. 50
Oxygen And Nitrogen Containing Organic Compounds
groups decreases the polarity of
Since ethers do not have a hydrogen atom bonded to the oxygen, they do not undergo hydrogen bonding between their molecules. Therefore, ethers are more volatile than their corresponding alcohols. H3C
O
CH3
CH3
dimethyl ether b.p : – 24.9 °C
CH2
OH
ethyl alcohol b.p : 78.3 °C
The boiling points of ethers increase as their molar masses increase. Like other organic compounds, branching lowers the boiling points of ethers. Since ethers are polar, they dissolve in water by forming hydrogen bonds. The solubility of ethers decrease when the molar masses increase. Ethers dissolve many polar and nonpolar substances very well.
Name
Formula
Melting
Boiling
Density
Point (°C)
Point (°C)
(g/mol)
Dimethyl ether
CH3OCH3
– 138
– 24.9
0.661
Diethyl ether
CH3CH2OCH2CH3
– 116
34.6
0.714
Dipropyl ether
(CH3CH2CH2)2O
– 122
90.5
0.736
Diisopropyl ether
(CH3)2CHOCH(CH3)2
– 86
68.0
0.735
Methyl butyl ether
CH3(CH2)3OCH3
– 116
70.3
0.744
Dibutyl ether
(CH3CH2CH2CH2)2O
– 95
141.0
0.769
1,2-dimethoxyethane
CH3OCH2CH2OCH3
– 68
83.0
0.863
Anisole (methoxybenzene)
C6H5OCH3
– 37.3
158.3
0.994
Table 2: Physical properties of some ethers
26 Put the following compounds in order of decreasing boiling points,
Since all the compounds have the same molecular formula, C 4H10O, their molar masses are equals, so there is no difference in boiling points due to the molar masses. These molecules are members of different classes. Alcohols and Ethers
51
The first one is an alcohol, the second and the third ones are ethers. Alcohols have higher boiling points than ethers because of their hydrogen bonding. Since the third compound has branching, it has a lower boiling point than the second ether compound. So the decreasing order of boiling points is I > II > III.
10. CHEMICAL PROPERTIES OF ETHERS In ethers, the oxygen atom is attached to two carbon atoms. Therefore, chemically, ethers resemble alkanes rather than water or alcohols. Ethers are stable and do not have an affinity for bases, oxidants or reductants. In this respect, they behave like alkanes and differ from alcohols. When ethers are heated with concentrated strong acid halides they undergo decomposition reactions. Alcohols and alkyl halides are the products. R
O
C2H5
R+H O
X
R
O
H+R
X
C2H5OH + C 2H5I
C2H5 + HI
27 0.2 mole of diethyl ether reacts with a sufficient amount of concentrated HBr solution. How many grams of which alcohol is obtained at the end of the reaction? (C2H5OH : 46 g/mol)
The reaction of diethyl ether with concentrated HBr solution is: C2H5
O
C2H5 + HBr
C2H5OH + C 2H5Br
1 mol of ethyl alcohol is produced from 1 mol of diethyl ether. From 0.2 mol of diethyl ether, 0.2 mol of ethyl alcohol is produced. Molar mass of C 2H5OH is 46 g/mol. m m n = –––––– then, 0.2 = ––––––––––––– M 46 g/mol m = 9.2 grams of ethyl alcohol is obtained. Ethers are flammable substances. Simple members of the aliphatic ethers are particularly volatile, because of this if ethers are used in a laboratory, care must be taken if there are any flames present. 3n CnH2n+2O + –––– O2 2 C2H5 52
O
nCO2 + (n+1)H2O
C2H5 + 6O2
Oxygen And Nitrogen Containing Organic Compounds
4CO2 + 5H2O
28 How many grams of diethyl ether can be burned in 336 L of air at STP? (C : 12 g/mol, H : 1 g/mol, O : 16 g/mol)
The combustion reaction of diethyl ether is: C2H5OC2H5 + 6O2 4CO2 + 5H2O Mol number of air used: 336 n = ––––––– = 15 mol 22.4 20 Since 20 percent of air is oxygen, 15 . ––––––– = 3 mol 100 reaction.
oxygen is used in the
According to the equation, 6 mol of oxygen reacts with 1 mol diethyl ether. For 3 mol of oxygen 0.5 mol of diethyl ether is required. M of diethyl ether : C2H5OC2H5 = (4 . 12) + (10 . 1) + 16 = 74 g/mol Mass of diethyl ether : m = n . M = 0.5 . 74 = 37 g
11. PREPARATION OF ETHERS Ethers are generally synthesized by two methods.
Dehydration of Alcohols When alcohols are dehydrated in the presence of a H 2SO4 catalyst, alkenes or ethers are produced. The temperature of the reaction medium determines whether the product is an alkene or ether. Formation of an ether takes place at a lower temperature than the formation of an alkene. 2R
OH
H SO
2 4 R
140 °C
alcohol
H2SO4
140 °C
methanol
R + H2O
ether
OH
2CH3
O
H3C
O
CH3 + H2O
dimethyl ether
Only symmetrical ethers can be obtained from these reactions proceeding in the presence of an acid catalyst.
Alcohols and Ethers
53
The Williamson Synthesis of Ethers This method is used in the presence of a basic catalyst to produce both symmetrical and unsymmetrical ethers. The reacting substances in these reactions are alkyl halides and metal alkoxides. By using the correct reactants, desired ethers may be obtained. Metal halide salts are produced as co-products. R
X+R
C2H5
O– Na+
R
O
O– Na+
I + C 3H7
R + NaX C2H5
O
C3H7 + NaI
12. DIETHYL ETHER Diethyl ether is the most commonly known ether and is called simply “ether” in daily life. Diethyl ether is a colorless, volatile, flammable liquid with a characteristic pleasant odor. It causes fainting when inhaled, which explains its use as an anaesthetic in medicine. Diethyl ether is a good solvent for organic compounds and is also used to remove H2O in organic reactions. Diethyl ether is also used both in the Wurtz synthesis and in the preparation of Grignard Reagents. In the laboratory ether is produced by dehydrating 1 mole of H 2O from 2 moles of ethyl alcohol. 2C2H5OH ethyl alcohol
H2SO4
140 °C
C2H5OC2H5 + H2O diethyl ether
Diethyl ether is a highly flammable liquid. Take care when you use ethers in the laboratory. 54
Oxygen And Nitrogen Containing Organic Compounds
1.
Write the structural formulae of the following compounds
a. Isopropyl alcohol b. Isobutyl alcohol
c. Cyclobutanol d. Tert-pentanol e. Glycol f.
Neo-pentanol
g. 3-ethyl-3-methyl-2-pentanol h. 2,2-dimethyl-1,4-hexandiol i.
1,3-butandiol
j.
3-butene-1-ol
3.
k. 3,3-dichlorocyclohexanol
2.
Arrange the following compounds in order of decreasing melting points. I. CH3CH2OH
II. CH3CH3
III. HOCH2CH2OH
Give the names of the following compounds.
4.
Write the structural formulae and the names of the alcohols which have the molecular formula of
a. C3H8O b. C4H10O
5.
Explain the primary, secondary and tertiary alcohol terms by giving an example of each.
6.
Classify the given alcohols as primary, secondary or tertiary.
7.
Explain the terms monoalcohols, dialcohols and trialcohols by giving an example for each of them. Give their general formulae. Alcohols and Ethers
55
8.
9.
Why do alcohols show both polar and nonpolar properties. Explain. While the solubility of isobutyl alcohol is 100g/100 cm3 of H 2O, that of ethyl alcohol is infinite. Explain why.
10. When 0.05 mol of a monoalcohol is burned, 2.2 grams of CO2 is produced. How many liters of oxygen gas are
d. C2H5OH + HI e. CH3CH2CH
heat, pressure
catalyst
f. CH3OH + HCOOH g. CH3CH2CH2OH + CH3Br h.
used at STP? (CO2 : 44 g/mol)
CH2(g) + H2O
+ CH 3 MgCl
+HCl
–MgCl2
11. If 5.4 grams of H2O is added to a sample of an alkene, 26.4 grams of a monoalcohol is obtained. What is the molecular formula of the alcohol?
i.
+ C 2H5 MgCl
+HCl
–MgCl2
12. When 13.8 grams of a primary alcohol reacts with Na metal, 3.36 L of H2 gas is ev olved at STP.
+ K 2Cr2O7 + H 2SO4
j.
a. Find the molecular formula of the alcohol. b. Name the product. 13. 10 gram of 2-butanol is oxidised by an excess amount of acidic KMnO4 solution and the reaction occurs with 74% efficiency. What is the mass and molecular formula of the substance produced?
14. How many grams of ethanal are obtained when 69 grams of ethyl alcohol are oxidised? 15.
I. If water is added to 2-butene, product A is obtained. II. At the end of the oxidation of A, compound B is obtained. Give the products A and B.
16. 6.3 grams of propylene reacts with water. The formed substance is added to an excess amount of KMnO4 under heat and acidic media. How many grams of product is formed?
17. What possible products can be obtained if cyclopentanol is heated in concentrated H2SO4 solution?
k. C3H5(OH)3 + O 2 20. When 106 grams of a mixture of cyclopentanol and water reacts with excess Na, 44.8 L of H2 is produced at STP. Find the mole percentage of cyclopentanol in the mixture.
21. What are the factors that affe ct the solubility of alcohols in water?
22. What are the meanings of simple and complicated ethers? Explain with examples.
23. Give the IUPAC and common names of the following compounds
a. CH3
CH2
O
CH2
CH3
b. CH3
CH2
O
CH2
CH2
18. How many alcohols with the molecular formula C5H12O
a. C2H5OH + O2 b. CH3CH2CH2
Cl + NaOH
Oxygen And Nitrogen Containing Organic Compounds
c. CH3OH + K 56
can be found? Give their structural formulae.
19. Complete and balance the following equations.
CH3
24. Write the molecular formulae of the following compounds.
34. Which of the following are ethers?
a. Methyl isopropyl ether
b. Ethyl phenyl ether
c. Dipropyl ether
d. Divinyl ether
25. What is the molecular formula of the simple ether that contains 52.17% carbon, 34.78% oxygen and 13.04% hydrogen by mass?
26. If a 73 gram mixture of ethyl alcohol and diethyl ether is burned, 85.12 L of CO2 gas is produced at STP. What is the mass percentage of diethyl ether in the mixture?
27. If a 25 gram mixture of methanol and diethyl ether is treated with sodium metal, 5.6 L of H2 gas is evolved at STP. What is the mass percentage of ether in the mixture?
35. Give the products if the following compounds are heated in a strong acidic medium at 140 °C. a. n-butanol b. cyclopentanol
28. Equal masses of acid and monoalcohol react to give 51 g of an ester and 0.5 mol water. Find the molar mass of the alcohol.
c. 2,2-dimethylbutanol 36. Which alcohols are used as reactants to produce the following ethers?
29. Write the equations of each step for the oxidation of methanol.
a. CH3CH2
O
30. Why is methyl alcohol is known as wood alcohol? Explain.
31. Why is glycol preferred as antifreeze in automobiles over ethyl alcohol? Explain.
32. What is the main reason of using glycerine in so aps and cosmetics? Explain.
CH2CH3
33. Write the names of following compounds. a. CH3
CH2
O
b. CH3
CH2
CH2
c. CH3
O
d.
CH
CH2
CH3
O
CH2
CH2
37. Arrange the following compounds in the order of decreasing boiling point. CH
CH2
I. CH3CH2CH2 II. HO
OH
CH2CH2CH2
OH
III. CH3CH2CH3 IV. CH3CH2
O
CH3 Alcohols and Ethers
57
1.
5.
Which one of the following compounds is not an isomer of the others? A) CH3CH2CH2CH2OH
B) CH3
O
C) C2H5
A) 2–hydroxy–2–ethyl–3–methylpentane
B) 3–hydroxy–3–methyl–4–ethyl
O
D) 3–hydroxy–3,4–dimethylhexane
Which one of the following bonds is not found in the structure of alcohols? C
B) C D) C
H
O
E) 4–hydroxy–3–methylpentane
A) C
C2H5
C) 3–hydroxy–3–methyl–4–ethyl
2.
C3H7
Which one of the following names is correct for the given compound?
C) H E) H
6.
CH3
O
C2H5
For the given compound,
O
I. It is ethyl methyl ether.
H
II. Hydrogen bonds exist between the molecules of the compound. III. It is an isomer of iso-propyl alcohol. Which of the above st atements above is/are true?
3.
A) I only
Which one of the following alcohols doesn’t have an ether isomer? A) CH 3O H
B ) C2H 5O H
D) C4H9OH
D) I and II
E) I, II and III
E) C5H11OH
What is the name of the hydrocarbon in which two methyl, one ethyl and one hydroxy group are attached to a carbon atom? A) 2– methyl – 2 – butanol B) 2– methyl – 2 – hydroxy– propane C) 2,2 – dimethyl – 2 – hydroxy – propane D) n – pentanol E) 2– pentanol
58
C) II and III
C) C3H7OH
7. 4.
B) I and III
Oxygen And Nitrogen Containing Organic Compounds
Which of the following gives the correct comparison for the above compounds with respect to their boiling points? A) I > II > III D) II > I > III
B) III > II > I
C) I = II = III
E) III > I > II
8.
I. Isopropyl alcohol and dimethyl ether
11.
I. n-pentanol
II. 2 – butanol and ethyl methyl ether
II. Isopentanol
III. 3 – pentanol and ethyl propyl ether
III. Neopentanol
Which of the given pairs of compounds are isomers?
Which is true for the melting point comparison of the above compounds?
A) I only
B) II only D) II and III
C) III only A) I = II = III
E) I, II and III
B) I > II > III
D) III > I > II
9.
C) I > III > II
E) III > II > I
What is the molecular formula of the monoalcohol that contains 60% carbon by mass? A) CH 3O H
B ) C2H 5O H
C) C3H7OH
A) 1
10.
12. At least how many carbon atoms are found in a tertiary alcohol?
B) 2
C) 3
D) 4
E) 5
13. Some compounds and their first oxidation products are given below.
Which of the names below can be used to correctly name the above compound? I. Isobutanol
II.
II. Tertiary butanol
III.
III. Trimethyl carbinol A) I only
B) II and III D) I and II
Compound ————————— I. Primary alcohol
Oxidation product ————————— Aldehyde
Secondary alcohol
Ketone
Tertiary alcohol
Carboxylic acid
Which is/are co rrect? C) III only E) I, II and III
A) I only
B) I and II D) III only
C) II and III E) I, II and III
Alcohols and Ethers
59
14. When ethyl alcohol is oxidised by two degrees, which one of the following products results?
17. Which one of the following c ompounds is produced by the primary oxidation of butane-2-ol?
A) Acetaldehyde
B) Acetic acid
A) Ethyl methyl ketone
C) Oxy-propane
D) Dimethyl ether
B) Dimethyl ketone
E) Dimethyl ketone
C) 2-butanol D) Butanoic acid E) Diethyl ketone
15. While using an equal mass of ethyl alcohol, the following substances are produced. I. Ethylene II. Ethane III. Acetic acid Which one of the given c omparison is true, if the mass of products are compared? A) I>II>III
B) III>II>I
D) II>III>I
C) I=II=III E) III>I>II
18. For the given compounds having the same number of carbon atoms; I. Primary alcohol II. Secondary alcohol III. Tertiary alcohol Which one is true fo r their boiling point comparison? A) I > II > III
B) I = II = III
D) I > III > II
16. CH2
CH
CH2
C) III > II > I
E) III > I > II
OH
For the given compound, I. Its aqueous solution has basic properties. II. It forms esters with carboxylic acids. III. It fades the color of an aqueous solution of bromine.
the molar mass of the other product obtained?
Which of the above statements is/are true? A) I only
B) III only D) II and III
60
19. From the reaction of 4.6 grams of a monoalcohol with Na metal, 1.12 L of H2 gas is obtained at STP. What is
C) I and II E) I, II and III
Oxygen And Nitrogen Containing Organic Compounds
(C : 12, H : 1, O : 16, Na : 23) A) 45
B) 46
C) 68
D) 70
E) 72
20. 2.24 L of H2 gas is evolved after the reaction of a 20
23.
grams mixture of C2H5OH and CH3OCH3 with Na metal. What is the mass percentage of dimethyl ether in the mixture? A) 46
B) 54
C) 82
D) 18
For 1 mole of the above organic compound, I. It reacts with 3 mol of Na.
E) 72
II. When 1 mol is reacted with a sufficient amount of Na metal, 3/2 mol of H2 gas is evolved. III. It reacts with 1 mol of Zn. Which of the above st atements is/are true? A) I only
B) II only
D) I and III
C) I and II E ) I, II and III
21. In acidic medium, CH3OH reacts with KMnO4 solution, to give the following reaction: 5CH3OH + 4KMnO4 + 6H 2SO4
24.
5HCOOH + 4MnSO4 + 2K2SO4 + 11H2O
C2H5OH
[O]
[O]
[O]
X Y 2Z + 2H2O –H2O
For given reaction,
How many grams of CH3OH react with 400 mL, 0.1 M
I. The compound X is acetaldehyde.
KMnO4 and how many grams of HCOOH are produced
II. The compound Y is acetic acid.
by the reaction?
III. The compound Z is carbon dioxide.
CH3OH
HCOOH
–––––––––––
–––––––––––––
A)
1.6
2.30
B)
3.2
4.60
C)
1.6
1.15
D)
2.4
3.45
E)
4.8
2.30
Which of the above s tatements is/are true? A) I only
B) II only D) II and III
25.
C) I and II E) I, II and III
For the above compound, which one of the following names cannot be used? A) 2–methyl–2–butanol
22. How many liters of CO2 gas are produced by the com-
B) 2–methyl–2–hydroxybutane
bustion of 0.5 mole of diethyl ether with a sufficient amount of oxygen gas?
C) Tertiary pentanol
A) 44.8
E) 2-pentanol
B) 22.4
C) 16.8
D) 8.96
E) 5.6
D) Dimethyl ethyl carbinol
Alcohols and Ethers
61
S t
c
a
p
y
a
i t
A
c
F P
p
i t
g
A f
l
h
b
p i
t
g
t s
y o
– L
W
– Alcohols containing two or more hydroxyl groups in their molecules are called __________________ – Ethers are isomers of these compounds. – L W – These alcohols can not be oxidized because they do not have a H atom on the carbon atom bearing the –OH group – L W
– L
W
– Boiling points of ethers ____________ as their molar masses increase – This describes compounds whose molecules have a hydroxyl group attached to a saturated carbon atom – The simplest alcohol – Alkyl magnesium halides (R–Mg–X) are also known as ____________ reagents – L W
– In the second oxidation of primary alcohols these compounds are produced. – This describes compounds in which the carbon that bears the –OH group is attached to only one other carbon. – L W
– These compounds are formed when secondary alcohols are oxidised. – L W
– In the first oxidation of primary alcohols these compounds are produced. – The IUPAC name of this compound is 1, 2, 3, propanetriol.
– This describes compounds in which an oxygen atom is attached to two carbon atoms. – Ethers that have the same alkyl groups bonded to the oxygen atom are called ________________ ethers.
62
Oxygen And Nitrogen Containing Organic Compounds
– Since it has a low freezing point it is used as antifreeze in automobiles.
INTRODUCTION The
Some Greek Letters Capital Small Name letter letter ————— ————— ————— Alpha
Beta Gamma Delta
group is known as the carbonyl group in organic compounds.
This group is found in aldehydes, ketones, carboxylic acids, esters and acid derivatives and is the main functional group in compounds such as amides. In this group, the carbon atom is sp 2– hydridized. As a result of the hybridization, three sigma () bonds and one pi ( ) bond are formed. Sigma bonds, which lie in a plane with bond angles of 120°, are present between the carbon–oxygen and carbon-alkyl groups.
Nu
Since the carbonyl group contains different atoms, it is polar. In the C
Pi
oxygen is much more electronegative than carbon and so, electron density in the
Rho
bond is displaced towards the oxygen atom. This results in the double bond elec-
Sigma
trons being shifted towards the oxygen atom.
O bond,
So in the carbonyl group, the oxygen atom is partially negative and the carbon atom is partially positive. From X–ray experiments, the length of the C
O bond
in the carbonyl group is found to be 1.22 A° .
1. ALDEHYDES Compounds in which one hydrogen atom and one carbon atom are bonded to the carbon atom in the carbonyl group are called aldehydes.
Aldehydes are represented by the general formula,
or RCHO.
groups are the functional groups of aldehydes.
R may be an alkyl or aryl group. The general formula of aliphatic aldehydes is CnH2nO. The simplest member of the aldehydes is formaldehyde and has two hydrogen atoms bonded to the carbonyl group.
1 What is the molecular formula of the aldehyde that contains 40% carbon by mass? (C : 12 g/mol, H : 1 g/mol, O : 16 g/mol) 64
Oxygen And Nitrogen Containing Organic Compounds
The molar mass of the aldehyde that has the molecular formula C nH2nO is (12n + 2n + 16) or (14 n + 16) g/mol. Mass of carbon is 12n gram. As stated in the question 40% of the aldehyde by mass is carbon. So in 100 grams aldehyde there must be 40 grams carbon. To find the number of moles of carbon, the following proportion is considered. 100 g aldehyde contains
40 g C
(14n+16) g aldehyde contains 12n g C –––––––––––––––––––––––––––––––––––––––––––––––– 40 · (14n + 16) 12n = –––––––––––––––––––– , so n = 1 100 If n = 1, the molecular formula is CH 2O, formaldehyde.
2 What is the molecular formula of the aldehyde that has a density of 1.80 g/L at room conditions? (C : 12 g/mol, H : 1 g/mol, O : 16 g/mol) (Hint : At room conditions a mol of gas occupies 24.5 L)
d = 1.80 g/L means that 1 L of this aldehyde weighs 1.80 g. Since 1 mole of gas occupies 24.5 L at room conditions, the mass of 24.5 L of aldehyde will give the molar mass of the aldehyde. M = 1.80 g/L · 24.5 L/mol 44 g/mol According to this, the molar mass of C nH2nO is 44 g/mol. So, 12n + 2n + 16 = 44 and n = 2. The molecular formula of the aldehyde is C2H4O .
2. NOMENCLATURE OF ALDEHYDES The longest chain of carbon atoms containing the aldehyde group is selected, and the chain is numbered assigning “1” to the carbon of carbonyl group. Substituents attached to the longest chain are given names and numbers. The name of the aldehyde is taken from the alkane with the same number of carbon atoms by changing the –e ending to -al.: Aldehydes and Ketones
65
Many aldehydes also have common names
The positions of substituents on the chain may be indicated by the letters , , , in aldehydes beginning with the carbon atom closest to the aldehyde group.
3 Name the following compounds.
66
a. 3,3 – dimethylpentanal
d. 3 – phenylpropanal
b. 2 – hydroxypropanal
e. 2 – ethyl – 3,3 – dimethylpentanal
c. 2,2 – dimethylbutanal
f. 2 – ethyl – 3 – hydroxybutanal
Oxygen And Nitrogen Containing Organic Compounds
4 Write structural formulae of the following compounds.
a. Isobutanal b. 2, 3, 4 – trihydroxybutanal c. p – methylbenzaldehyde d. 2 – bromopropanal
3. PHYSICAL PROPERTIES OF ALDEHYDES Because of the carbonyl group
, aldehydes are polar molecules.
In this structure, the oxygen atom is not bonded to a hydrogen, so there is no
hydrogen bonding between aldehyde molecules. Consequently, they have lower
boiling points than the corresponding alcohols but higher boiling points than the
corresponding ethers.
Formaldehyde is a gas at room temperature. The C 2 to C11 aldehydes are liquids and aldehydes higher than C 11 are solids at room temperature. The carbonyl oxygen atom allows molecules of aldehydes to form strong hydrogen bonds with water molecules. As a result, low molar mass aldehydes show appreciable solubilities in water. As the molar mass increases, polarity decreases
Low molar mass aldehydes dissolve in water due to hydrogen bonding. Hydrogen bonds are formed between the oxygen atom of the aldehyde and the hydrogen atom of water and also between the hydrogen atom of the alde hyde and the oxygen atom of water.
because of the effect of the hydrocarbon groups, hence the solubility in water also decreases.
Aldehydes and Ketones
67
The lower molar mass aldehydes have a sharp odor, though the odor becomes more fragrant as the molar mass increases. Thus, many aldehydes are used in perfumes and for food flavoring.
Name
Formula
Melting
Boiling
*Density
Solubility
Point (°C)
Point (°C)
(g/mL)
(g/100 mL water)
Formaldehyde (Methanal)
HCHO
–
Acetaldehyde (Ethanal)
CH3CHO
Propionaldehyde (Propanal)
92
– 21
0.815
very soluble
– 125
21
0.783
very soluble
CH3CH2CHO
– 81
49
0.806
very soluble
n – Butyraldehyde (Butanal)
CH3(CH2)2CHO
– 99
76
0.817
soluble
n – Valeraldehyde (Pentanal)
CH3(CH2)3CHO
– 91,5
102
0.810
slightly soluble
Caproaldehyde (Hexanal)
CH3(CH2)4CHO
– 51
131
0.833
slightly soluble
Benzenecarbaldehyde (Benzaldehyde)
C6H5CHO
– 26
178
1.42
slightly soluble
* Densities are given according to 20°C.
Table 1: Properties of some aldehydes.
4. CHEMICAL PROPERTIES OF ALDEHYDES Aldehydes have a high tendency to undergo chemical reactions because of their polar carbonyl group. Aldehydes have a hydrogen atom attached to the carbonyl group which makes them more active than ketones. Because this hydrogen atom is held only loosely, aldehydes undergo oxidation reactions. Also aldehydes may undergo addition reactions by opening up the bond in the carbonyl group. Addition of hydrogen, a reduction, reaction is also possible. Let's examine the oxidation, addition, polymerization and combustion reactions of aldehydes.
4.1. OXIDATION REACTIONS Aldehydes are readily oxidized, like alcohols, by strong oxidizing agents such as KMnO4, K2Cr2O7 or K2CrO4 in the presence of acids. They form carboxylic acids.
68
Oxygen And Nitrogen Containing Organic Compounds
In addition to this, aldehydes are also oxidized by some oxidizing agents such as Tollens’, Fehling's and Benedict's reagents. These reactions are characteristic reactions of aldehydes.
Tollens' Reagent
Tollens’ Test (Silver Mirror Test) Mixing aqueous silver nitrate with aqueous ammonia produces a solution known as Tollens’ reagent. The reagent contains the diamminosilver (I) ion
(Ag(NH 3)2+).
During the test silver is reduced from the +1 oxidation state to metallic silver as it oxidizes aldehydes to carboxylate ions.
This reaction can be shown more simply like this.
Tollens' B : 3 g of NaOH is dissolved in
Equal volumes of Tollens' A and Tollens' B solutions are mixed. Diluted ammonia is then added to the mixture until the formed silver oxide dissolves. This solution should not be prepared well in advance, or heated, otherwise a black precipitate forms. The minimum amount of NH3 should be used
30 cm3 of water, and put in a dark colored bottle. Then it is closed tightly. 30 cm3 of water, and put in a dark colored bottle. Then it is closed tightly.
Tollens' A : 3 g of AgNO 3 is dissolved in
Tollens' reagent reacts with some aldehydes in cold conditions and some aldehydes in hot conditions. Metallic silver, produced in the reaction, is deposited on the walls of the vessel (silver mirror) or it precipitates. This reaction is used to detect the presence of an aldehyde or to distinguish between aldehydes and ketones.
a.
b.
c.
a. Put the aqueous silver nitrate and aqueous ammonia solutions into the clean beaker. b. You can see that color of the solution darkens. As ethanal is oxidized to ethanoic acid, Ag+ ions are reduced to metallic silver. c. Metallic silver is deposited on the walls of the beaker as a mirror. All aldehydes under go this same reaction.
Silver mirror test
5 Write an equation for the reaction of each of the following with Tollens' reagent.
a. formaldehyde b. acetaldehyde c. benzaldehyde Aldehydes and Ketones
69
Tollens’ Reagent Bernard Tollens was German chemist and in 1881 first used this complex sil ver solution to detect aldehydes.
6 1 gram of a mixture of glycol-acetaldehyde reacts with Tollens' reagent to produce 1.08 g of a metallic silver. What is the percentage of acetaldehyde by mass in the mixture? (C: 12 g/mol, H: 1 g/mol, O: 16 g/mol, Ag: 108 g/mol)
Tollens' reagent is a mild oxidizing agent so only acetaldehyde is oxidized in the glycol-acetaldehyde mixture. As a result, metallic silver is produced. The equation for this reaction is as follows:
First let's find the mol number of Ag. 1.08 g n = ––––––––––––– = 0.01 mol 108 g/mol According to the equation, 1 mol acetaldehyde produces 2 mol Ag. To produce 0.01 mol Ag, 0.005 mol acetaldehyde must react. Molar mass of acetaldehyde; CH3CHO : 44 g/mol. That means 1 mol acetaldehyde is 44 g and 0.005 mol acetaldehyde is equal to 44 g/mol · 0.005 mol = 0.22 g So, we can find the percentage of acetaldehyde in the mixture. in 1 g mixture
0.22 g acetaldehyde
in 100 g mixture x g ––––––––––––––––––––––––––––––––––––––––––––––––––– x = 22 g The percentage of aldehyde by mass in the mixture is 22% . 70
Oxygen And Nitrogen Containing Organic Compounds
Fehling’s Test Fehling's solution is a basic solution of copper (II) ions complexed with sodium or potassium tartrate. When Fehling's solution reacts with aldehydes Cu +2 ions, which are a dark-blue color c olor in the complex, are reduced to brick-red copper (I) oxide (Cu2O). At the same time, the aldehyde is oxidized to the carboxylate ion (RCOO–).
Aromatic aldehydes aldehydes are oxidized by Tollens' Tollens' reagent, but not by Fehling's Fehling's reagent. This property is used to distinguish between aliphatic and aromatic aldehydes.
Ethanal, which boils at 21°C, is the colorless liquid in the test tube. Ethanal, which evaporates in the test tube, passes over heated copper(II) oxide (CuO), in the mouth of test tube, and turns into ethanoic acid. The acid changes the color of the litmus paper held in the mouth of test tube to red.
Fehling’s Reagent Fehling's I : 34.64 grams of pure copper sulfate (CuSO 4 . 5H2O) are dissolved in the
minimum amount of water containing a few drops of H2SO4 . Then, the volume of solution is diluted to 500 ml by adding water. Fehling's II : 60 gram of NaOH and 173 grams Rochelle salt (sodium potassium tar-
trate, NaKC4H4O6) are dissolved in water and diluted to 500 mL.
The solutions when mixed are unstable so they should be in stored in separate bottles with the lid sealed tightly. When used, equal volumes of the solutions should be mixed.
7 Write the reactions of Fehling's Fehling's reagent with formaldehyde and acetaldehyde.
Aldehydes and and Ketones
71
8 10 grams of propanal solution react with Fehling's reagent to produce 11 grams of Cu2O. What is the percentage of propanal by mass in the solution? (C : 12 g/mol, H : 1 g/mol, O : 16 g/mol, Cu : 63.5 g/mol)
Reaction equation;
The molar mass of propanal = 58 g/mol. The molar mass of Cu 2O=143 g/mol. to form 143 g of Cu 2O
58 g of propanal is used
to form 11 of Cu 2O x –––––––––––––––––––––––––– –––––––––––– ––––––––––––––––––––––––––– ––––––––––––––––––––––––––– ––––––––––––––––––––––– ––––––––– x = 4.46 g propanal There is 4.46 g of propanal in 10 g of solution. Percentage of propanal by mass can be found by proportions. in 10 g of solution
4.46 g of propanal is present
in 100 g of solution x g of propanal is present ––––––––––––––––––––––––––––––––––––––– –––––––––––––––––––––––––– ––––––––––––––––––––––––––– –––––––––––––––––––––––––––– ––––––––––––––––– ––– x = 44.6 So there is 44.6% of propanal in the solution.
Reactions with KMnO4 Aldehydes reduce potassium permanganate. While the aldehyde is oxidized to a carboxylic acid, Mn 7+ in KMnO4 is reduced to the Mn 2+ ion. During the reaction, the violet color of potassium permanganate disappears.
9 3.6 grams of an aldehyde reacts with 100 mL of a 0.2
M
of KMnO4 solution until
the color of the solution disappears. What is the molecular formula of the carboxylic acid produced? (C : 12 g/mol, H : 1 g/mol, O : 16 g/mol) 72
Oxygen And Nitrogen Containing Organic Compounds
The mol number of KMnO 4 is n =
M
· V = 0.2 · 0.1 = 0.02 mol. The reaction
equation of an aldehyde with KMnO 4 solution is;
–
According to the equation 2 mol of MnO4 reacts with 5 mol of aldehyde. So, –
0.02 mol of MnO4 reacts with 0.05 mol aldehyde. 0.05 mol aldehyde is
3.6 g
1mol aldehyde is x –––––––––––––––––––––––––––––––––––––––– ––––––––––––––––––––––––––– –––––––––––––––––– ––––– x = 72 g 29 g of 1 mol of aldehyde belongs to the functional group (MCHO = 12 + 1 + 16 = 29 g/mol) 72 – 29 = 43 g belongs to the alkyl group. CnH2n+1 = 43 g/mol. So, 12n + 2n + 1 = 43 14n + 1 = 43 n = 3 Since the alkyl group must be C3H7 , the molecular formula of the aldehyde is C3H7CHO. Since the aldehyde contains 4 carbon atoms, the produced carboxylic acid will also have 4 carbon atoms in its structure. So the molecular formula of the carboxylic acid is C3H7COOH.
4.2. ADDI ADDITION TION REACTI REACTIONS ONS OF ALDEHYDE ALDEHYDES S The most common reactions of compounds containing the carbonyl group are addition reactions. In these reactions, the bond in the carbonyl group is broken. Atoms or groups of atoms can bond with the carbon and oxygen atoms. Because of the electronegativity differences, the carbon atom is partially positive (+), and the oxygen atom is partially negative ( –).
The electronegativity value of carbon is 2.5 and that of oxygen is 3.5.
So in addition reactions, positively charged (+) atoms or groups of atoms, bond to the oxygen atom and negatively charged (–) ones bond to the carbon atom.
Addition of Hydrogen Aldehydes react with H2 in the presence of a nickel platinum catalyst to form primary alcohols. The reaction is slow and occurs only under certain conditions.
Aldehydes and and Ketones
73
Nowadays, metal hydrides are widely used to reduce aldehydes. The most important are lithium aluminum hydride (LiAlH 4) and sodium borohydride (NaBH 4).
In this process, NaBH4 reduces only the carbonyl group, while LiAlH4 reduces both the carbonyl group and any unsaturated carbon atoms in the hydrocarbon chain.
Addition of Water When aldehydes react with water, unstable hydrate compounds are formed. In this process, the hydrogen atom of water is bonded to the oxygen in the carbonyl group and the hydroxide group of water is bonded to the c arbon atom of the carbonyl group.
74
Oxygen And Nitrogen Containing Organic Compounds
Dissolving an aldehyde in water results in the establishment of an equilibrium between the aldehyde and its hydrate. In the aqueous solutions of low-molar mass aldehydes, the hydrate ratio is much higher than in longer chained aldehyde solutions.
These hydrates are unstable and can not be obtained pure.
Addition of Alcohol Alcohols can be added to aldehydes in the presence of an anhydrous acid catalyst. The alkoxide part (RO –) of the alcohol is attached to the carbon atom of the carbonyl group of the aldehyde and the proton (H +) from the alcohol is attached to the oxygen of the aldehyde. The new compound is called a hemiacetal.
Hemiacetals show properties of alcohols due to the presence of the
group and react with large amounts of alcohol in the presence of an acid to produce acetal compounds which have the properties of e thers. This reaction is not an addition reaction. All the steps in the formation of an acetal from an aldehyde are reversible.
Aldehydes and and Ketones
75
HCN is a very harmful toxic gas. The frightening thing is that its odor can be noticed only when it reaches deadly lev-
Acetals do not react with same reactants as aldehydes because the ether bonds in acetals give them a different structure.
els.
Addition of HCN Addition of HCN to aldehydes produces cyanohydrins. Since HCN is a toxic gas, –
it is not used in the reaction directly. CN salts of active metals such as Na and K react with mineral acids such as H3PO4 and then the HCN formed reacts with
Millipedes and HCN Millipedes spray a toxic gas to protect themselves. They carry mandelanitrile (benzaldehyde cyanohydrine) in their protective glands. When they are attacked, cyanohydrine and an enzyme are mixed to produce benzaldehyde and HCN. This is then sprayed at the attacker. A millipede can spray enough HCN to kill a mouse.
the carbonyl group. While it is n ecessary to use an acid catalyst to react poor nucleophiles like H 2O and ROH with aldehydes, there is no need to use a catalyst for a strong nucle–
ophile such as CN .
Addition of Grignard Reagents Addition of Grignard reagents to aldehydes is the most important method of preparing of alcohols. The product of these reactions is a kind of alkoxide. This alkoxide hydrolyses in the presence of acid and forms an alcohol. You may remember that to prepare primary alcohols by this method we should start with formaldehyde, and to prepare secondary alcohols we should start with higher aldehydes.
76
Oxygen And Nitrogen Containing Organic Compounds
Addition of NaHSO3 In these reactions, the hydrogen in NaHSO 3 attaches to the oxygen of the car– bonyl group and NaSO 3 attaches to the carbon of the carbonyl group. In this reaction there is no need for an acid catalyst. The reaction is at equilibrium in aqueous solution and the aldehyde can be reformed from the sodium hydrogensulfite addition product by adding acid or base to the reaction mixture.
Generally, sodium hydrogensulfite addition products of higher molar mass aldehydes can be precipitated easily. Hence NaHSO3 is often used to separate aldehydes from mixtures.
10 Write out the addition reactions of acetaldehyde with the following substances under suitable conditions.
a. Hydrogen, b. Water, c. Methyl alcohol, d. NaHSO3
Aldehydes and Ketones
77
4.3. POLYMERIZATION Aldehydes undergo polymerization reactions under certain conditions. In these reactions, as the aldehyde molecules react with different functional groups to form polymers. Polymers formed when the bonds of the aldehyde molecules open and bond to each other are called homopolymers. Addition reactions like these are also called parapolymerization reactions. In polymerization reactions, mineral acids are used as catalysts and the formed product may be a ring or a linear structure.
Because aldehyde polymers do not contain aldehyde groups, they do not show the properties of aldehydes. The boiling points of these polymers are higher than those of the corresponding aldehydes. Polymerization reactions of aldehydes are reversible, linear polymers being decomposed more easily than ring polymers. Decomposition is easier under higher temperatures and in the presence of concentrated acids.
4.4. COMBUSTION REACTION The combustion products from the burning of aldehydes are CO 2 and H2O. The reaction is exothermic. The general combustion reaction of aldehydes is: 3n–1 CnH2nO + ––––––– O 2 2 C3H6O + 4O2
nCO2 + n H 2O
3CO2 +3H2O
11 2.464 L of oxygen at STP is required to burn 1.44 grams of an aldehyde. What is its molecular formula? (C : 12 g/mol, H : 1 g/mol, O : 16 g/mol) 78
Oxygen And Nitrogen Containing Organic Compounds
Let us find the number of moles of oxygen gas in the reaction. 2.464 L moles of O 2 = ––––––––––– = 0.11 mol 22.4 L/mol Combustion reaction of aldehydes; CnH2nO +
3n – 1 ––––––––– O2 2
nCO2 + n H 2O
According to the equation 1 mol of aldehyde reacts with (3n–1)/2 mol O 2. Because 1 mol aldehyde is (14n + 16) g, we can find number of carbon atoms in the aldehyde by using proportions. 3n – 1 (14n+16) g of aldehyde reacts with (–––––––––) mol of O 2 2 1.44 g of aldehyde reacts with 0.11 mol of O2 –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– 3n – 1 0.11 (14n + 16) = 1.44 · ––––––––– 2 n=4 By putting 4 into the general molecular formula, the aldehyde is found to be C4H8O.
5. PREPARATION OF ALDEHYDES 5.1. OXIDATION OF PRIMARY ALCOHOLS Aldehydes are readily prepared by the oxidation of alcohols. Oxidation of primary alcohols with a catalyst produces aldehydes. Their oxidation state lies between that of primary alcohols and that of carboxylic acids.
In this reaction K2Cr2O7 is used as the oxidizing agent. Aldehydes and Ketones
79
Condensation Reactions Aldehydes undergo condensation reactions with different substances. In condensations reactions, two molecules form a larger molecule.
12 Which alcohols need to be oxidized to produce following aldehydes?
a. Formaldehyde b. 2 – methylpropanal c. 2,2 – dimethylbutanal
Aldehydes are obtained by the oxidation of primary alcohols. During the oxidation process, there is no change in the carbon chain of the alcohol. However, the alcohol group is turned into an aldehyde group. According to this information:
a. There is one carbon atom in the structure of formaldehyde. So there should be just one carbon atom in the structure of the alcohol. This is methanol.
b. 2 – methylpropanal is obtained from 2 – methylpropanol. c. 2,2 – dimethylbutanal is obtained from 2,2 – dimethylbutanol.
80
Oxygen And Nitrogen Containing Organic Compounds
5.2. DEHYDROGENATION OF PRIMARY ALCOHOLS Aldehydes are obtained from primary alcohols by removing H2 in the presence of a copper chromite (CuO · Cr2O3) catalyst. To do this, alcohol vapor at 250-300 °C is passed over hot CuO · Cr2O3 . One hydrogen molecule from each alcohol molecule is removed in the reaction. Thus, the alcohol is oxidized to an aldehyde. A hydrogen molecule can also be removed from low molar mass alcohols using just CuO as the catalyst.
If H 2 is removed from a molecule, it is called dehydrogenation. If H 2 is added, it is called hydrogenation. Hydrogenation is a reduction reaction and dehydrogenation is an oxidation reaction. As aldehydes are formed by the dehydro genation of alcohols, their names are derived from the first syllables (al- and dehyde-) of these words.
a
Heat copper foil in a bunsen burner.
b
Reduction of Carboxylic Acid Just as the oxidation products of aldehydes are carboxylic acids, the reduction products of carboxylic acids are aldehydes. To carry out this reaction, any carboxylic acid with formic acid is passed in gaseous state over a catalyst of TiO 2 at 300-350°C. As a result, an aldehyde is obtained and CO 2 and H2O are given out.
It is seen that the copper foil is covered with black copper (II) oxide (CuO)
c
6. SOME IMPORTANT ALDEHYDES 6.1. FORMALDEHYDE Formaldehyde is a colorless gas with a pungent odor. It is the simplest aldehyde and was discovered by the Russian chemist A. Butlerov in 1859. It is readily soluble in water and it is most commonly used as a 40% solution in water known as formalin. Formaldehyde is widely used to manufacture building materials and numerous household products.
Hot copper oxide reacts with ethyl alcohol, it quickly oxidizes the ethanol to ethanal and it itself is reduced to bright metallic copper as before. Dehydrogenation of primary alcohols Aldehydes and Ketones
81
Formaldehyde hardens proteins and prevents them decaying. Hence, it is used to store biological products, to make mummies and also as a disinfectant as it kills insects and microorganisms. Formaldehyde exhibits most of the general chemical properties of aldehydes though is more reactive than other aldehydes. Formaldehyde undergoes the Cannizzaro reaction to produce formic acid and methanol.
For storing biological products formalin solution, an aqueous solution of formaldehyde 40% by mass, is used.
Formaldehyde also undergoes addition, condensation, and polymerization reac Did you know that formaldehyde and many harmful chemicals are found in shoe polish? As a result of being exposed to shoe- polish, asthma is often found in people working in shoe-shine shops. Experts advise people who suffer from allergies to polish their shoes in places such as balconies or other well-vent ilated areas. It should also be emphasized t hat these paints should be kept out of the reach of small children.
tions. The most interesting addition reaction of formaldehyde is the addition of ammonia. In this reaction hexamethylene tetramine (urotropine) is formed. This is used in medicine to clean urethras, in industry to harden resins and is also added to foodstuffs as a preservative.
Formaldehyde is easily polymerized by opening the double bond between the carbon and oxygen atoms. When formaldehyde gas is kept at room temperature, a white solid trimer is formed. This trimer, which has a ring structure, is known as trioxymethylene, metaformaldehyde or trioxan.
This polymer dissolves in water and does not have the properties of aldehydes. When it is needed, formaldehyde can be produced by heating trioxymethylene. 82
Oxygen And Nitrogen Containing Organic Compounds
When formaldehyde is heated, a white crystalline polymer that melts at 123 °C is obtained. This polymer, known as paraformaldehyde, is formed from between 50
a
to 100 monomers of formaldehyde. It is a linear polymer and decays into formaldehyde when heated.
When formaldehyde is heated with concentrated sulphuric acid, it forms the polymer polyoxymethylene, which contains at least 100 monomers. Polyoxymethylene is linear like paraformaldehyde. The main difference between the two of them is the number of monomers in the polymer. When heated, it also decays into formalde-
Dilute HCl is poured into a solution of formaldehyde, acetic acid and phenol.
b
hyde. It is widely used in the textile industry. Formaldehyde is obtained by the oxidation of methyl alcohol. In the laboratory, acidic solutions of KMnO4, K2Cr2O7 or K2CrO4 can be used as the oxidizing agent. 5CH3OH + 2KMnO4 + 3H2SO4 5HCHO + K2SO4 + 2MnSO4 + 8H2O The bitter, stinging smell of the produced formaldehyde is observed during the reaction. In industry, formaldehyde is obtained by heating a methanol and air mixture. This reaction is the dehydrogenation of methanol (Hoffman method). The process is carried out by using the oxygen from the air with a catalyst of copper and silver.
c
When the mixture is stirred it heats up and its color turns pink. This indicates that the polymer is forming.
6.2. ACETALDEHYDE Pure acetaldehyde is a colorless, volatile and poisonous liquid that is miscible with water. The boiling point of acetaldehyde is 21 °C.
As a result of stirring the solution for one minute, solid phenolformaldehyde, a condensation polymer is formed. This polymer can be pulled from the mixture with the stirring rod.
Acetaldehyde is used for synthesizing of many organic compounds such as acetic acid, ethyl alcohol and synthetic rubber.
Formation of a polymer Aldehydes and Ketones
83
Acetaldehyde undergoes polymerization reactions similar to formaldehyde. Acetaldehyde reacts with itself in the presence of H2SO4 at room temperature to form paraldehyde, a trimer, though at 0 °C it forms methaldehyde, a tetramer.
Acetaldehyde is an air pollutant emitted by cars and certain production facilities. It is also contained in tobacco smoke. It is classified as a probable carcinogen.
Do you know?!
Paraldehyde, which boils at 124 °C, has a pleasant fruity smell. It causes people to feel sleepy, and is hence used for hypnosis in medical science. It changes back to acetaldehyde when boiled with dilute H 2SO4 . Methaldehyde is a solid that sublimes at 112 °C. It was given to soldiers in World War I to heat their meals under the name of solid ethyl alcohol.
Acetaldehyde forms resins when boiled in strong concentrated basic solutions. Many acetaldehyde molecules attach together to form a linear polymer.
84
Oxygen And Nitrogen Containing Organic Compounds
7. KETONES Compounds with two alkyl groups or aryl groups attached to t he carbonyl group are known as ketones.
The general molecular formula of ketones is C nH2nO. So aldehydes and ketones having same number of carbon are structural isomers of each other.
8. NOMENCLATURE OF KETONES 8.1. COMMON NAMES Common names use the names of the R (alkyl groups) or Ar (Arene group) as separate words, along with word ketone.
13 Name the following compounds.
a. Ethyl isopropyl ketone
b. Benzyl phenyl ketone
c. Methyl tertiary butyl ketone
d. Phenyl isopropyl ketone
8.2. USING THE IUPAC SYSTEM The longest carbon chain containing the carbonyl group is selected and numbered starting with the carbon atom nearest the carbonyl group. If substitutents are present on the main chain, they are indicated by number of the carbon atoms to which they are attached. The number of the carbon atom of the carbonyl group is added to the front of the ketone. The IUPAC system replaces the –e of the name of the corresponding alkane by the suffix –one. Aldehydes and Ketones
85
14 What are the IUPAC names of the following compounds?
a. 3 – methyl – 2 – butanone b. 3 – methyl cyclopentanone c. 2,3 – butadione d. 3,3 – dimethyl – 2 – butanone e. 3 – methyl cyclohexanone f. 2 – pentanone g. 1 – phenyl – 3 – bromo – 2 – butanone h. 2,2 – dichloro – 3 – pentanone
9. PHYSICAL PROPERTIES OF KETONES Low molar mass ketones are liquids. Ketones with more than C 11 atoms are solids. Liquid ketones readily dissolve in water as they form hydrogen bonds with water molecules. Liquid ketones are used as solvents in the preparation of paint chemicals. Solubility of ketones decreases with increasing size of the molecule. Ketones, compared to aldehydes, have more pleasant odor. 86
Oxygen And Nitrogen Containing Organic Compounds
Ketones are polar molecules because of the carbonyl group, but there is no hydrogen bonding between the molecules. The polarity of ketones decreases with increasing size of the groups attached to the carbonyl group. The polarity of ketones is much greater than that of ethers, hence ketones boil at higher temperatures than hydrocarbons and ethers with similar molar masses but boil at lower temperatures than corresponding alcohols.
Name
Structure
*Solubility in Melting Boiling *Density Water (g/100 mL Point Point (g/mL) H2O) (°C) (°C)
Acetone
CH3COCH3
– 95
56
0.790
2 – Butanone
CH3COCH2CH3
– 86
80
0.805
very soluble
2 – Pentanone
CH3COCH2CH2CH3
– 78
102
0.812
soluble
3 – Pentanone
CH3CH2COCH2CH3
– 39
102
0.816
soluble
2 – Hexanone
CH3CO(CH2)3CH3
– 57
127
0.830
slightly soluble
Acetophenone
CH3COC6H5
21
202
1.028
insoluble
Benzophenone
C6H5COC6H5
48
306
1.100
insoluble
* The values are given for 20°C.
Table 2: Some ketones and their physical properties.
15 Arrange the following compounds, all with the general formula (C 4H8O), in order of decreasing boiling point. III. CH2
II. CH3CH2CH2CH2
CHCH2CH2
OH
IV. CH2
CH
O
OH CH2CH3
Compound I is a ketone, II is a primary alcohol, III is a primary alcohol of alkene derivation and IV is an ether derivative. So the order of decreasing boiling points are II, III, I and IV. Aldehydes and Ketones
87
10. CHEMICAL PROPERTIES OF KETONES Since ketones do not have a hydrogen atom directly bonded to their carbonyl group they don't behave as reducing agents like aldehydes. They are rather resistant towards oxidation and can be used for many oxidation reactions as sol vents. However, when they are heated with very strong oxidizing agents for a long time, their carbon chains are broken. As a result, the ketone is either oxidized to a carboxylic acid or is decomposed. Ketones do not react with Tollens', Fehling's or Benedict's reagents. Under specific conditions, symmetric ketones may be oxidized to two different carboxylic acids, and unsymmetric ketones oxidized to four different acids.
Carbon and oxygen atoms become active by the breaking of the bond in the ketone carbonyl group. Even though ketones are less reactive than aldehydes, they undergo all the same addition reactions as aldehydes.
10.1. ADDITION REACTIONS Addition of Hydrogen (Reduction of Ketones) Hydrogen can be added to ketones using metal catalysts such as Ni, Pt and Pd to form secondary alcohols. In these reactions, the ketones are reduced.
Addition of Water By adding water to ketones, unstable ketone hydrates are formed. In this process, the hydrogen of water attaches to the oxygen of the carbonyl group and the hydroxyl group of water attaches to the carbon of the carbonyl group. Ketone hydrates and ketones are in equilibrium in aqueous solution. 88
Oxygen And Nitrogen Containing Organic Compounds
Addition of Alcohol Alcohols can be added to ketones in the presence of anhydrous acids. In the reaction, the alkoxide part of the alcohol (RO –) is attached to the carbon of the carbonyl group and the proton from the alcohol (H +) is attached to the oxygen of the ketone.
Ketones form hemiketals upon reaction with alcohols. Because of the
COH
group, hemiketal compounds display the properties of alcohols and can react further with alcohols to form ketal compounds which have the properties of ethers.
Addition of HCN Ketones form cyanohydrin compounds upon the addition of HCN. Since HCN is a toxic gas, it is not used directly in the reactions, instead, the NaCN salt is t reated with a mineral acid (such as H 2SO4).
Aldehydes and Ketones
89
Ketones having large groups attached to the carbonyl group do not undergo addition reactions with HCN.
Addition of Grignard Reagents Addition of Grignard reagents (RMgX) to ketones is one of the most important preparation methods of alcohols. The addition products hydrolyse in the presence of an acid to form tertiary alcohols.
Addition of NaHSO3 Ketones, apart from acetone and aromatic ketones, do not react with NaHSO 3 . In the addition process of the ketones that do react, hydrogen from NaHSO 3 –
attaches to the oxygen of the carbonyl group and NaSO3 attaches to the carbon of the carbonyl group. The product is a crystalline solid. In this reaction, there is no need for a catalyst.
NaHSO3 is used to separate ketone compounds, especially acetone, from mixtures. 90
Oxygen And Nitrogen Containing Organic Compounds
16 Assuming suitable conditions, write out the addition reactions of dimethyl ketone with following substances.
a. Hydrogen
b. Water
c. Methyl alcohol
d. HCN
e. CH3 MgCl/H2O
f. NaHSO3
17 What is the molecular formula of the alcohol obtained by adding 2.8 L H 2 at STP with 9 grams of ketone? (C : 12 g/mol, H : 1 g/mol, O : 16 g/mol) Aldehydes and Ketones
91
Number of mol H 2
2.8 L n = ––––––––––– = 0.125 mol. 22.4 L/mol
Ketones undergo an addition reaction with H 2 gas according to the following equation.
According to the equation, 1 mol H2 reacts with 1 mol ketone. So, 0.125 mol H 2 reacts with 0.125 mol ketone. 0.125 mol ketone is
9g
1 mol ketone is x g ––––––––––––––––––––––––––––––––––– x = 72 g The molar mass of the ketone is 72 g/mol. And, according to reaction given above molar mass of alcohol must be 74 (molar mass of ketone and hydrogen) As we know that (–CH–OH) group in alcohol has 30 grams mass, then, 74 – 30 = 44 grams must be total mass of the remaining part of alcohol. Consequently, the molecular formula of the alcohol is
18 Which ketone should be used to prepare tertiary butanol by the addition of a Grignard Reagent?
The molecular formula of tertiary
Ketones have 2 alkyl groups and at
butanol is
least 3 carbon atoms, in the structure of a Grignard reagent, there is 1
alkyl
group.
ketone
Oxygen And Nitrogen Containing Organic Compounds
the
Grignard
reagent must be CH3 MgX and the
92
So,
19 What is the molecular formula of a simple ketone if 0.2 mole of the product that is produced by the reaction of this ketone with HCN weighs 22.6 grams?
Addition of HCN to ketones occurs according to the following equation.
Let us find the molar mass of the product. 0.2 mol compound
22.6 g
1 mol compound x g ––––––––––––––––––––––––––––––––––––––––––––––– x = 113 g Since the molar mass of the compound R(R )C(CN)OH is 113 g/mol, 55 g/mol of this belongs to the (
C(CN)OH) group and 113 – 55 = 58 g/mol belongs to
the alkyl groups. Because the ketone is symmetrical, the alkyl groups are the same. So, the molar mass of one alkyl group is 58 g/mol / 2 = 29 g/mol. So, the alkyl group is C2H5 and the molecular formula of the ketone is
20 What is the molar mass of the ketone of which 0.2 mole of its addition product with sodium hydrogensulfite weighs 35.2 grams? (C : 12 g/mol, H : 1 g/mol, O : 16 g/mol, S : 32 g/mol, Na : 23 g/mol)
Addition of sodium bisulfite to a ketone occurs according to the following equation.
The number of moles of product equals that of the ketone. So the molar mass of the product can be calculated. Aldehydes and Ketones
93
M = 35.2 g / 0.2 mol = 176 g/mol.
In this compound, the molar mass of the (SO 3Na) OH group is M = S + (3 . O) + Na + O + H = 32 + (3 . 16) + 23 + 16 + 1 = 120 g/mol Consequently, the molar mass of the
group is 176 – 120 = 56 g/mol
Therefore the molar mass of the ketone
is
56 + 16 = 72 g/mol.
21 A 1 mole of acetaldehyde and acetone undergoes an addition reaction with an excess amount of methanol to form 97 grams of addition product. According to this information, what is the mass of acetone in the initial mixture? (C4H10O2 : 90 g/mol)
The mixture of acetaldehyde - acetone reacts with methanol as follows:
At the beginning, if there is x mole of acetaldehyde there is, (1 - x) mole of acetone. According to the first equation, 1 mole of acetaldehyde produces 1 mole of product, so x mole of acetaldehyde produces x mole of product. The molar mass of the formed 1,1 - dimethoxyethane is 90 g/mol. and the mass of the compound is m = n . M = 90 x g According to the second equation, 1 mole of acetone produces 1 mole of ketal compound, so (1 - x) mole of acetone produces (1 - x) mole of ketal compound. 94
Oxygen And Nitrogen Containing Organic Compounds
The molar mass of the ketal compound is MC
5H12O2
= (5 . 12) + (1 . 12) + (2 . 16) = 104 g/mol
and the mass of the compound is m = n . M = (1 – x) . 104 g The sum of the mass of these two compounds should be 97 grams. 90 x + [(1 – x) . 84] = 97 x = 0.5 mol In 1 mole of mixture, there is 0.5 mol of acetaldehyde and 1 – 0.5 = 0.5 mol of acetone. According to this, the mass of acetone in the mixture is m = n . M = 0.5 mol . 58 g/mol = 29 g
10.2. COMBUSTION REACTION Combustion reaction of ketones are exothermic. General combustion reaction of ketones occur according to the following equation. 3n–1 CnH2nO + ––––––– O 2 nCO2 + n H 2O 2 C3H6O + 4O2 3CO2 +3H2O
11. PREPARATION OF KETONES 11.1. OXIDATION OF SECONDARY ALCOHOLS Ketones are formed by oxidising secondary alcohols. The boiling points of ketones are lower than those of the corresponding alcohols. As mentioned pre viously, oxidation can occur with different reactants under different conditions.
Aldehydes and Ketones
95
11.2. DEHYDROGENATION OF SECONDARY ALCOHOLS One hydrogen molecule and a ketone are formed when secondary alcohols in the vapor state are passed over CuO · Cr 2O3 granules.
11.3. HEATING CALCIUM SALTS OF CARBOXYLIC ACID The dry distillation of the calcium salts of carboxylic acids produces ketones.
11.4. ADDITION OF WATER TO ALKYNES By adding of water to alkynes other than acetylene, ketones are produced. The addition reaction occurs in the presence of H2SO4 and HgSO4 catalysts.
96
Oxygen And Nitrogen Containing Organic Compounds
12. ACETONE Acetone, also called propanone or dimethyl ketone, is the smallest ketone. It is a colorless, volatile liquid with a pleasant odor. The boiling point of acetone is 56 °C. It can mix with water, alcohol and ether in all proportions. It is a wonder-
The most familiar household use of acetone is as the active substance in nail polish remover.
ful organic solvent, dissolving varnishes, lacquers, resins, plastics, paints, oils and their derivatives. A large amount of acetone is present in people who suffer from diabetes and consequently their urine contains a considerable amount of acetone. Hence the urine of diabetes sufferers will give off a distinctive acetone odor. Acetone burns with a blue dull flame. It is very difficult to oxidize, though possible when reacted with strong oxidizing agents. Acetone is different to other ketones in that it may be polymerized.
12.1. PREPARATION OF ACETONE Distillation of Wood The distillation product of wood contains 0.5% acetone. It may be isolated by fractional distillation.
Heating of Calcium Acetate Acetone is obtained from the dry heating of the calcium acetate salt. However, the yield of th e reaction is low.
Oxidation of Isopropyl Alcohol Acetone is obtained from the oxidation of isopropyl alcohol, a secondary alcohol.
Preparation of acetone from calcium acetate.
Oxidation occurs with oxidizing agents such as acidified KMnO 4 solution.
In addition, acetone may be obtained by the reaction of isopropyl alcohol vapor with air at high temperatures in the presence of Cu and Ag catalysts.
Aldehydes and Ketones
97
From Acetic Acid Preparation of acetone in high yields can be achieved by passing acetic acid vapor over a metal oxide catalyst such as MgO, CaO or Al 2O3 .
22 A formaldehyde-acetone mixture contains 80% acetone by mass. When this mixture reacts with Fehling's reagent, 14.3 gram of solid Cu 2O is produced. What is the total mass of th e mixture? (C : 12g/mol,
H : 1 g/ mol, O : 16 g/mol, Cu : 63.5 g/mol)
When an acetone - formaldehyde mixture reacts with Fehling's reagent, acetone does not participate. However, formaldehyde reacts according to the following equation. HCHO + 2Cu+2 + 4OH–
HCOOH + Cu2O + 2H2O
MCu2O : (2 . 63.5) + 16 = 143 g/mol MHCHO : (2 . 1) + 12 + 16 = 30 g/mol According to the equation, 30 grams of formaldehyde forms 143 grams of Cu 2O. The mass of formaldehyde in the mixture is found by the proportion method. 143 grams Cu2O is produced from
30 grams of HCHO
14.3 grams Cu2O is produced from x gram HCHO ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– x = 3 g If 80% of mixture is acetone, 20% of mixture is formaldehyde, 20% of formaldehyde is 3 grams. 20% mixture
3 grams
100% mixture x grams ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– x = 15 grams So the mass of the mixture must be 15 grams. 98
Oxygen And Nitrogen Containing Organic Compounds
1.
Name the following compounds.
4.
a. 3 – penten – 2 – al
b. 2 – methylbutanal
c. 4 – nitrobenzaldehyde
f. 4–bromo–2–methylpentanal
e. 2,3 – dihydroxyhexanal
d. 3,3,3 – trichloropropanal
Give the molecular formulae for the following compounds.
5.
Write down the molecular formulae of aldehydes containing.
a. 1 carbon atom b. 2 carbon atom c. 3 carbon atom 2.
Give the common and IUPAC names of these compounds.
Give the IUPAC names of the following compounds.
6.
a. C4H8O
b. C5H8O
7.
The compounds given below first react with C2H5 MgBr and then with HBr. Give the molecular formulae and the names of the products.
Draw the structural formulae of the following compounds, their common names are given.
3.
c. C5H10O
Draw the structural formulae of the aldehyde compounds having the following molecular formulae.
a. Propionaldehyde b. Isobutyraldehyde c. – hydroxyvaleraldehyde d. Phenylacetaldehyde
Which aldehydes are obtained when the following alcohols are oxidized?
e. – bromobutyraldehyde
a. Ethyl alcohol
b. Neopentyl alcohol
f. o – hydroxybenzaldehyde
c. 2 – methylbutanol
d. Isobutyl alcohol
8.
Aldehydes and Ketones
99
9.
When 1 gram of a mixture of formaldehyde - formic acid Ag+
reacts with Tollens' reagent, ions are reduced to Ag (metallic silver). In total, 5.4 grams of Ag metal are formed. What are the mass percentage of formic acid in the mixture?
10. When 15 grams of a monoalcohol is oxidized, 5. 6 L of gaseous aldehyde is obtained at STP. What is the molar mass of this aldehyde?
11. What is the molecular formula of the aldehyde that contains 69.77% C, 11.63% H and 18.60% O by mass?
12. Which functional groups does the compound vanillin, shown on the right, contain?
16. When 0.2 mol of an aldehyde is oxidized, 14.8 gram of a carboxylic acid is formed. What is the molecular formula of the aldehyde and its molar mass?
17. What is the molecular formula and the mass of the aldehyde that is formed from the oxidation of 18.4 gram, 80% ethyl alcohol?
18. Starting from aldehydes and by choosing appropriate reagents, show by using equations how the following compounds could be obtained? a. Ethyl alcohol b. Acetic acid c. Ethoxyethanal d. Propanoic acid
e. Acetaldehyde hydrate f. Acetaldehyde cyanohydrine g. Trichloroethanal
19. Write equations for the following reactions.
a. n – butanal + hydrogen
b. Isobutanal + ethanol c. Acetaldehyde + methanol d. Neopentanal + water
13. Compare the boiling points of liquids given below. Explain.
Ethyl alcohol C2H5OH
Dimethyl ether CH3OCH3
20. 40.4 gram of 1,2 - dibromopropane is treated with dilute KOH solution. The product reacts with H2O and is then oxidized. What is the mass of the substance that is formed at the end of the reaction?
Acetaldehyde CH3CHO
14. Compare the following compounds with respect to their solubilities in water.
(C : 12 g/mol, H : 1 g/mol, O : 16 g/mol, Br : 80 g/mol)
21. Ethylene dibromide, a. Is first heated with dilute NaOH solution and it turned into an alcohol. What is the molecular formula of this alcohol?
I. n – propanol II. n – propanal
b. Then, the alcohol is oxidized once by KM nO4. What is
III. n – butane
the molecular formula of the aldehyde produced and find its molar mass?
IV. Methoxyethane
I. Acetylene
15.
II. Acetylene chloride
22.
III. Ethyl alcohol IV. Isopropanol In which of the above compounds could an addition product be an aldehyde? 100
Oxygen And Nitrogen Containing Organic Compounds
What are X and Y in the reactions above ?
23. Starting from 0.25 mole of CaC2 how many grams of an aldehyde can be produced? Show with equations.
24. Acetaldehyde, aceton e and ethanol are present in three different containers. Explain in detail how you could determine which compound was in which container. 29. Complete and balance the following equations. 25. Using CaC2, H2, H2O and acidic K2Cr2O7 solution;
write out the synthesis reactions for these compounds. I. Acetylene
II. Acetaldehyde
III. Ethyl alcohol
IV. Acetic acid
26. Water vapor is reacted with acetylene gas in the presence of a HgSO4 catalyst. a. What is the name and the molecular formula of the compound produced? b. If 16.8 L of acetylene is used at STP in a reaction of 75% efficiency, what mass of compound is formed?
30. How many structures of ketones with the molecular formula C5H10O can be written? Draw them.
27. When
(hydroxyethanal) is reacted with a
a. Write its molecular formula
31. For acetone
large amount of acidic KMnO4 , what is the molecular formula and the molar mass of the new compound?
b. Give its lUPAC name c. Identify any aldehydes and ketones that are isomers of acetone.
28. Name the following compounds.
32. Which of the given compounds are aldehydes (if any) and why?
Aldehydes and Ketones
101
1.
3.
The above compound is correctly named by which of the following?
Compare the compounds above with respect to their boiling points.
A) 2,4 – dimethylpentanal B) 2,3 – dimethylpentanal
A) I > II > III
C) 2,3 – dimethyl – 1 – pentanol
B) III > II > I
D) II > I > III
D) 3 – ethyl – 2 – methyl – 1– butanal
C) I = II = III
E) III > I > II
E) n – heptanal
4.
+
–
CH3CHO + 2Ag + 3OH
–
2Ag + CH3COO + 2H2O
According to this equation, how many grams of metallic silver precipitates when 0.22 gram of CH3CHO is reacted?
2.
(C : 12 g/mol, H : 1 g/mol, O : 16 g/mol, Ag : 108 g/mol)
Which of the following aldehydes are named incorrectly?
A) 0.54
B) 1.08
C) 1.62
D) 2.16
E) 4.32
5.
This compound, I. is named as 2 – methylpropanal.
II. reacts with Na metal. III. reacts with Tollens' reagent.
A) I only D) I and III 102
Which of the statements abov e is(are) true ?
B) II only
C) III only E) II and IV
Oxygen And Nitrogen Containing Organic Compounds
A) I only
B) II only D) I and II
C) I and III E) I, II and III
6.
9.
Which one of the followin g compound s produces 2 – methyl – 3 – pentanone when it is partially oxidized? A) 2 – methyl – 3 – pentanol
For the above compound,
B) 2 – hydroxyhexane
I. When it reacts with Na, H2 gas is evolved
C) 2 – methyl – 2 – hydroxypentane
II. When it reacts with silver nitrate and ammonia, metallic silver precipitates.
D) 3 – methyl – 2 – hydroxypentanol E) n – hexanol
III. It undergoes an addition reaction with H2 . Which of the statements above is(are) true? A) I only
B) I and II
D) I and III
C) II and III
E) I, II and III
10.
I. Ethyl methyl ketone II. 2 – butanone III. Buten – 2 – one Which of the names above describe the compound correctly?
7.
+
RCHO + 2Ag + H 2O
+
RCOOH + 2Ag + 2H
A) I only
According to the equation above, 5.8 grams of aldehyde RCHO produces 21.6 grams of metallic silver. Which one of the following is the molecular formula of this aldehyde ?
B) I and II D) I and III
C) II and III E) I, II and III
(Ag : 108 g/mol, H : 1 g/mol, O : 16 g/mol)
11.
In the reaction above, 15.8 gram of (RCOO)2Ca produces 10 grams of CaCO3 .
How many C atoms are there in the structure of the produced ketone?
(Ca : 40 g/mol, C : 12 g/mol, H : 1 g/mol, O : 16 g/mol)
A) 3
12.
B) 4
C) 5
D) 6
E) 7
I. Methanal II. Ethanal III. Propanal
8.
Which one of the following compounds reduces the Ag+ ion in silver nitrate and ammonia solution? A) Aldehyde
B) Ketone
D) Carboxylic acid
C) Alkene E) Ester
Which of the compounds above do not have a ketone isomer? A) II only D) II and III
B) III only
C) I and II E) I, II and III
Aldehydes and Ketones
103
13.
17. Aldehydes,
I. can be oxidized.
II. can be reduced.
III. can produce polymers.
Which of the statements abov e is(are) tr ue?
A) I only
B) II only D) I and III
C) III only E) I, II and III
Which of the above compounds can not be oxidized? A) I only
B) II only D) II and III
C) III only E) I and III
18. Which one of the following is not a property o f ketones? A) They can be reduced. B) They can be oxidized.
14.
C) They undergo addition reactions.
D) The can be polymerized.
E) Combustion products are CO2 and H2O.
Which of the compounds above pre cipitate metallic sil ver when reacted with AgNO3 in ammonia solution? A) I only
B) III only D) II and III
C) I and III E) I, II and III
19. Some compounds have more than one name. Pairs of names are given below. I. Dimethyl ketone, acetone II. Methanal, formaldehyde III. Ethanal, acetaldehyde Which pairings repr esent the same compound? A) I only
I. Undergo reduction to form primary alcohols.
15.
B) II only D) II and III
C) I and II E) I, II and III
II. React with Fehling's reagent III. When they burn, CO2 and H2O are formed Which of the properties above apply to ketones? A) I only
B) III only D) II and III
C) I and III E) I, II and III
20. 3 methyl and an aldehyde group are attached to a carbon atom. I. 2,2 – dimethylpropanal II. Isopentanal III. n – pentanal
16. Which one of the following is formed when isopropyl alcohol is partially oxidized? A) Propanol
B) Dimethyl ethe r
D) Ethyl methyl ketone 104
C) Acetone
E) Propanoic acid
Oxygen And Nitrogen Containing Organic Compounds
Which of the names above represent this compound correctly? A) I only
B) I and II D) I and III
C) III only E) I, II and III
21. Which one of the following compounds forms acetone when it is partially oxidized?
–
25. CH3CHO + 2Cu+2 + 5OH
According to the above equation, how many grams of acetaldehyde are needed to precipitate 28.8 grams of Cu2O?
–
Cu2O + CH3COO + 3H 2O
(C : 12 g/mol, H : 1 g/mol, O : 16 g/mol, Cu : 64 g/mol)
A) 1.53
B) 9.2
C) 8.8
D) 2.35
E) 1.27
26.
22.
II. 2 – butanol
I. 1 – butanol
III. 2 – methylpropanol Which of the given alcohols form a ketone when oxidized?
A) I only
B) II only D) I and II
C) III only
E) II and III
Which of the above alcohols produce a ketone when oxidized? A) I only
B) II only
C) III only
D) I and II
E) II and III
23. The following statements describe formaldehyde, I. When it polymerizes with phenol, bakelite is obtained. II. When it reacts with ammonia, hexamethylene tetramine (urotropine) is formed. III. When it is partially oxidized, formic acid is formed. Which are true ?
27. For
A) I only
B) II only D) II and III
C) I and II
E) I, II and III
I. They are isomers of each other. II. They are isomers of 3 – methyl – 1– butanol.
24. To reduce 2.2 grams of acetaldehyde, how many liters of H2 are needed at STP? (C : 12 g/mol, H : 1 g/mol, O : 16 g/mol) A) 0.56
B) 1.12
C) 1.68
D) 2.24
III. They undergo an addition reaction with NH3 . Which of the above s tatements is (are) true? A) I only
E) 4.48
B) I and II D) I and III
C) II only
E) I, II and III Aldehydes and Ketones
105
D w G
h T
b
j t
u ( l
n
P
a n l t t r
m
L a
c
c u t
h b t f i t
l S
P t c M
s
i t
106
Oxygen And Nitrogen Containing Organic Compounds
INTRODUCTION
The group that is formed by the combination of a carbonyl
and hydroxyl
( OH) group is called the carboxyl Compounds that contain
group.
the carboxyl group are called carboxylic acids.
Most organic acids found in fruits and vegetables are carboxylic acids.
Carboxylic acids can be represented by R The R
COOH or
.
group can be aliphatic, aromatic or cyclic.
1. CLASSIFICATION OF CARBOXYLIC ACIDS Carboxylic acids can be separated into two groups; according to the number of carboxyl groups, or according to the different functional groups in their structures.
1.1. ACCORDING TO THE NUMBER OF CARBOXYL GROUPS Depending upon the number of carboxyl groups, acids can be classified as monocarboxylic acids or polycarboxylic acids.
Monocarboxylic Acids Acids which contain only one carboxyl group are called monocarboxylic acids. H
COOH
CH3
formic acid
COOH
C2H5
acetic acid
COOH
propionic acid
The general formula of monocarboxylic acids is C nH2n+1COOH or C nH2nO2. Here, n can be any integer.
Polycarboxylic Acids Acids which contain more than one carboxyl group are called polycarboxylic acids. If two carboxyl groups are present, the acid is a dicarboxylic acid and if there are three carboxyl groups the acid is a tricarboxylic acid. The general formula of a dicarboxylic acid is C nH2n(COOH) 2 and general formula of a tricarboxylic acid is C nH2n–1 (COOH) 3.
108
Oxygen And Nitrogen Containing Organic Compounds
1.2. ACCORDING TO THE FUNCTIONAL GROUPS Different functional groups may be attached to the carbon chain of a carboxylic acid. In this case, the classification of the acid is made according to the functional group.
Hydroxy Acids Carboxylic acids which contain the hydroxyl group are called hydroxy or oxy acids.
Hydroxy acids show both alcoholic and acidic properties because of the hydroxyl ( and the (
OH)
COOH) carboxyl groups.
Amino Acids Carboxylic acids which contain the amino group (
NH2) are called amino acids.
Amino acids show basic properties because of the amino group (
NH2) and acidic
properties because of the carboxyl group (
COOH), so they are amphoteric com-
pounds. Amino acids act as a base when they react with an acid and act as an acid when they react with a base, in both cases a salt is formed.
Keto Acids
The carbonyl (
) group in carboxylic
acids leads to keto acids.
2. NOMENCLATURE OF CARBOXYLIC ACIDS 2.1. COMMON NAMES Carboxylic acids have common names derived from Latin or Greek words that relate to their natural sources. For example, formic acid is obtained from ant secretions, in Latin, ant is formica hence the name formic acid. The names of acetic acid (acetum, vinegar), butyric acid (butyrum, butter) and stearic acid (stear, tallow) are derived in the same way. H
COOH
formic acid
CH3
COOH
acetic acid
C3H7
COOH
butyric acid
CH3CH2)16
COOH
stearic acid
Carboxylic Acids
109
If there are different substituents attached to the chain, their positions can be shown by the Greek letters –, –, –, –, – and so on.
Structure
Common Name
1
HCOOH
Formic acid
2
CH3COOH
Acetic acid
3
CH3CH2COOH
Propionic acid
4
CH3(CH2)2COOH
Butyric acid
5
CH3(CH2)3COOH
Valeric acid
6
CH3(CH2)4COOH
Caproic acid
7
CH3(CH2)5COOH
Enanthoic acid
8
CH3(CH2)6COOH
Caprylic acid
9
CH3(CH2)7COOH
Pelargonic acid
10
CH3(CH2)8COOH
Capric acid
Number of Carbon
Source Ant (L. formica) Vinegar (L. acetum)
Milk, butter, and cheese (Greek; protos, first; pion, fat)
Butter (L. butyrum) Valerian root (L. valere, being strong) Goats (L. caper)
Enantic (L. oenanthe, vine blossom)
Goats (L. caper)
Pelargonium roseum
Goats (L. caper)
Table 1: Common names of the first ten carboxylic acids and their sources.
2.2. USING THE IUPAC SYSTEM The longest chain containing the carboxyl group is selected. The chain is numbered beginning with the carboxyl carbon atom and substituents are located in the usual way. The locations of substituents are clarified by the number of the carbon atom to which they are attached. To obtain the name of the acid, -e from the name of the corresponding alkane is replaced by the suffix –oic and word acid is added.
110
If a carboxylic acid contains a carboxyl group at each end of the chain, the suffix –dioic acid is added to the name of corresponding alkane.
Oxygen And Nitrogen Containing Organic Compounds
If the carboxyl group in a compound is attached to a carbon other than those on the end of the chain, the prefix carboxy is used together with the location of the carboxyl group. If the carboxyl group is attached to a cyclic compound, the words carboxylic acid are added to the name of cyclic compound.
1 Give the IUPAC names for the following compounds.
a. 2 – chlorobutanoic acid
b. 2,3 – dibromopropanoic acid
c. 6 – aminohexanoic acid
d. 5 – cyanopentanoic acid 2
Write the structural formulae for the following compounds.
a. 2 – methylbutanoic acid b. 5 – aminopentanoic acid c. 2 – methyl – 3 – hydroxybutanoic acid d. 1, 5 – pentanedioic acid e.
– methyl –
f.
– oxypropionic acid
– chloropropanoic acid
Carboxylic Acids
111
3. PHYSICAL PROPERTIES OF CARBOXYLIC ACIDS The first three members of the saturated monocarboxylic acids are colorless liquids with a sharp odor. Carboxylic acids with carbon numbers between 4 and 9 smell of butter and almond oil. The smell of spoilt butter and cheese and the unpleasant odor of sweat is due acid formation. For example, butyric acid smells like butter because it is found in butter. Carboxylic acids having more than ten carbons are odorless, wax-like solids. The acids from C 14 to C22 are found in vegetable oils and fats and are known as fatty acids. Some of the physical and chemical properties of carboxylic acids are dependent upon the polarity of the carboxyl group. Acid molecules can form strong hydrogen Butter contains butyric acid. The amount of butyric acid increases when butter is spoilt, giving it an unpleasant odor.
bonds with each other and as a result carboxylic acid molecules can form dimers.
The boiling points of carboxylic acids are approximately 30-40 °C higher than those of hydrocarbons, alcohols, ethers, aldehydes and ketones of comparable molar mass. For example, ethyl alcohol boils at 78 °C and formic acid at
100.5 °C.
At room temperature, the C1 to C7 carboxylic acids are liquids and acids with
Because of the strong hydrogen bonds, carboxylic acid molecules form dimers. 112
more than 7 carbons are solids. Boiling points of carboxylic acids increase with increasing molar mass. However there is no regular change in the melting points of carboxylic acids. Carboxylic acids with an even number of carbon atoms melt at higher temperatures than similar acids with an odd number of carbon atoms.
Oxygen And Nitrogen Containing Organic Compounds
CH3COOH
C2H5COOH
C3H7COOH
m.p. 16.6 °C
m.p. –21.5 °C
m.p. – 8 °C
C4H9COOH m.p. –34 °C
Carboxylic acids dissolve in water because they form hydrogen bonds. As the number of carbon atoms increases, the effect of hydrogen bonding and hence the solubility in water decreases. The alkyl group (R the R
) has hydrophobic properties so as
group becomes larger, the hydrophobic properties of the acids increase.
The first four members of the carboxylic acids are soluble in water in any ratio. However the solubility of pentanoic acid is only 3.7 grams per 100 grams of water while that of decanoic acid is 0.2 grams. Higher carboxylic acids can be dissolved in ether, benzene or chloroform. IUPAC Name
Common Name
Formula
Melting Point (°C)
Boiling Point (°C)
8.5
100.5
*Solubility (g/100 mL water)
16.6
118
– 21.5
141
CH3(CH2)2COOH
–8
164
n – valeric acid
CH3(CH2)3COOH
– 19
187
4.97
Hexanoic acid
Caproic acid
CH3(CH2)4COOH
–3
205
1.08
Heptanoic acid
Enanthoic acid
CH3(CH2)5COOH
– 10.5
223
0.26
Propenoic acid
Acrylic acid
H2C
– 13
141
slightly soluble
Benzenecarboxylic acid
Benzoic acid
C6H5COOH
122
250
0.34
2 – hydroxybenzoic acid
Salicylic acid
159
211
0.22
189
149 -160 Sublimes
15.00
Methanoic acid
Formic acid
HCOOH
Ethanoic acid
Acetic acid
CH3COOH
Propanoic acid
Propionic acid
CH3CH2COOH
Butanoic acid
n – butyric acid
Pentanoic acid
CHCOOH
Ethandioic acid
(COOH)2
Oxalic acid
* at 25°C
Table 2: Physical properties of some carboxylic acids.
When carboxylic acids dissolve in water, hydrogen ions are formed and an equi-
librium is established. R
COOH(aq) + H2O(l)
COO–(aq)
R
+
H3O+(aq)
The acid ionization constant is defined by the formula: [R COO–] . [H3O+] Ka = ––––––––––––––––––––––––––––––– [R COOH]
formic acid
HCOO
–
+
+ H3O
Formic acid has the highest ionization constant (K a) HCOOH + H 2O
Carboxylic acids dissolve in water form ing hydrogen bonds with water molecules.
formate ion
Ka = 1.8 . 10–4 Carboxylic Acids
113
As the number of carbon atoms increases in an acid, ionization decreases, and hence the ionization constant (K a) decreases. Because of the decrease in the concentration of hydrogen ions, acidic strength decreases as shown in Table 3. Name
Ionization Constant (Ka)
Formula
Formic acid
HCOOH
1.8 · 10–4
Acetic acid
CH3COOH
1.8 · 10–5
Propanoic acid
CH3CH2COOH
1.3 · 10–5
2 – methylpropanoic acid
(CH3)2CHCOOH
1.6 · 10–5
2,2 – dimethylpropanoic acid
(CH3)3CCOOH
0.9 · 10–5
Butanoic acid
CH3(CH2)2COOH
1.6 · 10–5
Hexanoic acid
CH3(CH2)4COOH
1.30 · 10–5
Fluoroacetic acid
FCH2COOH
2.6 · 10–3
Chloroacetic acid
ClCH2COOH
1.4 · 10–3
Bromoacetic acid
BrCH2COOH
1.3 · 10–3
Dichloroacetic acid
Cl2CHCOOH
5.6 · 10–2
Trichloroacetic acid
Cl3CCOOH
2.3 · 10–1
Table 3: Ionization constants of some carboxylic acids in water at 25°C. –
When highly electronegative atoms or polyatoms, such as F, Cl, Br, S, NO 2 or OH– are attached to an acid, acidic strength increases.
The electronegativity of the attached atom or group effects the acidity directly. For example, as F is more electronegative than Cl, – fluoroacetic acid is stronger than – chloroacetic acid. Electronegative substances attract electrons from the carbon atoms they are attached to, this further polarizes the O
H bond making ionization of the acid
easier.
114
Oxygen And Nitrogen Containing Organic Compounds
Both the location and the number of electronegative substituents effect the acid strength. If the electronegative substituent is close to the carboxyl group or if the number of electronegative substituents is high, the polarization of the O
H
bond increases and thus acidic strength increases.
3 Compare the boiling points of the following compounds. I. C2H5OH II. CH3OCH3 III. HCOOH
I, II and III have equal molar masses of 46 g/mol. I is an alcohol, II is an ether and III is a carboxylic acid. There is no hydrogen bonding between ethers, so they are volatile. Alcohols and carboxylic acids both undergo hydrogen bonding, but because of the dimerization of carboxylic acids, they have the highest boiling point. Therefore the boiling point order is III > I > II . Carboxylic Acids
115
4 Calculate the pH of 0.5 (K = 1.8 . 10–5)
M
acetic acid.
a
Acetic acid dissociates into ions in water; CH3COOH(aq)
CH3COO– (aq) + H +(aq)
Ka = 1.8 . 10–5
Initial : 0.5 M – – Change : – x + x + x ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– at Equilibrium : (0.5– x) M x M x M Ka
[CH3COO–] . [H+] x . x 1.8 . 10–5 = ––––––––– x = 3 . 10–3 = ––––––––––––––––––– [CH3COOH] (0.5 – x)
M
+ [H ] = 3 . 10–3 M.
pH
+ = – log[H ] = – log (3 . 10–3)
pH
= 2.52
4. CHEMICAL PROPERTIES OF CARBOXYLIC ACIDS The reactions of carboxylic acids can be separated into two groups; bond cleavage of the O
H bond and bond cleavage of the C
H bond is broken,
H+
is produced and when the C
O bond. When the O O bond is broken, OH is
produced.
4.1. REACTIONS INVOLVING OF CLEAVAGE OF THE O — H BOND From the
COOH group, H+ ion leaves and a carboxylate salt forms. To obtain
the name of carboxylate anion, the suffix –oic acid is replaced by the suffix –ate. For example, CH3COO– is called acetate.
Salt Formation Carboxylic acids undergo reaction with active metals to form carboxylate salts and hydrogen gas. HCOOH + Na HCOONa + 1/2H2 formic acid
sodium formate
2CH3COOH + Mg (CH3COO)2 Mg + H2 acetic acid
116
Oxygen And Nitrogen Containing Organic Compounds
magnesium acetate
5 24 grams of a monocarboxylic acid reacts with an excess amount of Mg and 4.48 L hydrogen gas (H 2) is produced at STP. What is the molecular formula of the carboxylic acid?
Number of moles of H 2 gas. 4.48 L n = ––––––––––––––– = 0.2 mol 22.4 L/mol Reaction of carboxylic acid with Mg; 2R
COOH + Mg (RCOO)2 Mg + H2
amount of carboxylic acid used; 2 mol acid produces
1 mol H 2 gas
x mol acid produces 0.2 mol H2 gas ––––––––––––––––––––––––––––––––––––––––––––––– x = 0.4 mol molar mass of acid m n = –––––– M
m
24 g
n
0.4 mol
M = ––––– = –––––––––
M = 60 g/mol. Molecular formula of the carboxylic acid CnH2n+1COOH = (n . 12) + [(2n + 1) . 1] + 12 + 16 + 16 + 1 = 60 n=1
and formula is;
CH 3COOH
Neutralization Reactions Carboxylic acids react with bases in the same way as inorganic acids do to form salt and water. Because carboxylic acids are weak acids, their salts hydrolyse in solution and so carboxylic acid salt solutions show basic properties. R
COOH
+
carboxylic acid
HCOOH
NaOH
+
acetic acid
Ba(OH)2
2KOH
oxalic acid
H2O water
HCOONa + H 2O
(CH3COO)2Ba + 2H2O barium acetate
potassium hydroxide
+
sodium formate
barium hydroxide
+
COONa salt
sodium hydroxide
2CH3COOH
R
inorganic base
+
formic acid
NaOH
+ 2H2O
potassium oxalate
Carboxylic Acids
117
Reactions with Salts Carboxylic acids react with basic salts, such as CaCO 3 and NaHCO3 , to form CO2, salt and water. This reaction is used to differentiate between carboxylic acids and phenol and alcohol compounds, which also contain the
OH group. Alcohols and phenols
do not react with these basic salts. R
COOH + NaHCO3
R
2R
COOH + CaCO3
(R
COONa + CO2 + H2O COO)2Ca + CO2 + H2O
C2H5COOH + NaHCO 3
C2H5COONa + CO2 + H2O
2CH3COOH + MgCO 3
Mg(CH3COO)2 + CO2 + H2O
6 Complete the following reactions and give the names of the products.
a. CH3COOH + Zn
b. HCOOH + Al
c. C2H5COOH + Ba(OH) 2
d.
e. CH3COOH + KOH
f. CH3COOH + KHCO 3
+ KOH
g. 2CH3COOH + MgCO 3
a. 2CH3COOH + Zn (CH3COO)2Zn + H2 zinc acetate
b. 3CH3COOH + Al (CH3COO)3 Al + 3/2H2 aluminum acetate
Ba(C2H5COO)2 + 2H2O
c. 2C2H5COOH + Ba(OH) 2
barium propanoate
d.
+ 2KOH
+ 2H2O
potassium oxalate
e. CH3COOH + KOH
CH3COOK
+ H2O
potassium acetate
f. CH3COOH + KHCO 3
CH3COOK
+ CO2 + H2O
potassium acetate
g. 2CH3COOH + MgCO 3
(CH3COO)2 Mg + CO2 + H2O magnesium acetate
118
Oxygen And Nitrogen Containing Organic Compounds
4.2. REACTIONS THAT INVOLVE C — O BOND BREAKAGE The hydroxyl group (
OH) can be separated from the carboxyl group
by the cleavage of the C
O bond.
The group is called the acyl group. If a different functional group is attached to the acyl group other than the OH group, the compound is called an acid derivative.
Formation of Acid Anhydrides
If carboxylic acids are treated with dehydrating agents, acid anhydrides are formed.
The functional group of acid anhydrides is the
group.
Acid anhydrides are named by adding anhydride after the acid from which they
are derived.
Formation of an anhydride from an acid is similar to the formation of an ether from alcohols. When dicarboxylic acids are heated up to 200 – 300 °C, cyclic anhydrides with five or six carbons are formed.
An alternative way to produce anhydrides is by the reaction of alkali metal salts of carboxylic acids with acid chlorides. In addition to the anhydride, alkali metal salts are formed in this reaction. Carboxylic Acids
119
Esterification As you may remember from the alcohol chapter, esters are formed by the reaction of a carboxylic acid and an alcohol in the presence of a sulfuric acid, H 2SO4, catalyst. The hydroxyl group ( (R
OH) of the carboxyl group is replaced by the alkoxide
O) group in the esterification reaction.
7 Which carboxylic acid and alcohol pairs should be used to form the esters below?
120
Oxygen And Nitrogen Containing Organic Compounds
In X, the acyl group is
, and the alkoxide group is
. So X is formed from propanoic acid, (C 2H5COOH) and
secondary propanol, .
The acyl group of Y is
and the alkoxide group is
Therefore Y is formed from formic acid (HCOOH) and benzyl alcohol (C6H5CH2OH).
Z contains the same two acyl groups
and the alkoxide group
The alkoxide group is a derivative of glycol. So Z is formed from pentanoic acid and glycol (1,2 – ethanediol).
Formation of Acid Chlorides The hydroxyl group of carboxylic acids is replaced by chloride upon reaction with PCl3, PCl5 or SOCl2 . To obtain the name of the acid chloride, the suffix –oic acid is replaced by –oyl chloride.
RCOOH carboxylic acid
RCOOH carboxylic acid
+ PCl5
heat
+ SOCl2
RCOCl
+
POCl 3 + HCl
acid chloride heat
RCOCl acid chloride
+ SO2 + HCl
When acid chlorides hydrolyse in water, carboxylic acids form.
Carboxylic Acids
121
8 Write down the reactions of propanoic acid with the given compounds under suitable conditions.
a. PCl3
b. PCl5
c. SOCl2
4.3. ADDITION OF HALOGENS When a halogen is replaced by an NH 2,
SH or
OH,
CN group, a
hydroxy acid, amino acid, thiohydroxy
In the presence of a red phosphorous catalyst, chlorine and bromine react with carboxylic acids to produce – halo acids. When excess amounts of halogen are used, the number of substituted hydrogens increases.
acid or cyano acid is produced.
4.4. REDUCTION REACTIONS The reduction of carboxylic acids is difficult by catalytic hydrogenation. Carboxylic acids have to be reduced by strong reducing agents such as LiAlH 4 or NaBH4. The R 122
COOH group is reduced directly to
LiAlH4
COOH R
Oxygen And Nitrogen Containing Organic Compounds
CH2
OH
CH 2OH.
5. PREPARATION OF CARBOXYLIC ACIDS 5.1. OXIDATION OF PRIMARY ALCOHOLS AND ALDEHYDES Oxidation of primary alcohols produces aldehydes, and oxidation of aldehydes produces carboxylic acids. For these oxidation reactions KMnO 4 and K2Cr2O7 solutions are used in acidic medium.
If an excess amount of oxidizing agent is used, primary alcohols are oxidized to carboxylic acids directly.
5.2. OXIDATION OF AROMATIC COMPOUNDS Benzoic acid is prepared by the oxidation of alkyl benzenes. For the oxidizing agent, a hot, acidic solution of KMnO 4 or K 2Cr 2O7 is used. The number of carbon atoms attached to the aromatic structure, doesn't change the product.
Carboxylic Acids
123
5.3. OXIDATION OF ALKENES When alkenes react with a hot, basic solution of KMnO4 they are oxidized to carboxylic acids. If straight chain alkenes are used, monocarboxylic acids are produced. R
CH
CH3
CH
CH
KMnO4, OH–
R
COOH + R
R
heat
KMnO4, OH–
C2H5
CH
CH3
heat
COOH
COOH + C2H5
COOH
If cycloalkenes are used, dicarboxylic acids are produced.
5.4. CARBONATION OF GRIGNARD REAGENTS Preparation of carboxylic acids by the reaction of Grignard reagents with carbon dioxide is the most commonly used method.
Carbonation of Grignard reagents is similar to the addition of Grignard reagents to aldehydes and ketones. However, in the former reaction, carboxylate is produced, not alcohol. The magnesium carboxylate produced does not dissolve in ethers but when dissolved in acid, carboxylic acids are formed.
5.5. HYDROLYSIS OF CARBOXYLIC ACID DERIVATIVES H2O or the OH– ion may react with the carbonyl group of an ester to form carboxylic acids. For example esters can be hydrolyzed by heating with water in the presence of an acid catalyst. 124
Oxygen And Nitrogen Containing Organic Compounds
5.6. HYDROLYSIS OF NITRILES Carboxylic acids are produced by the hydrolysis of nitrile compounds. In the hydrolysis the
CN group is converted to the
COOH group. Nitriles can be
prepared by substitution reactions of alkyl halides with KCN or NaCN.
5.7. REACTION OF CARBOXYLATE SALTS When carboxylate salts react with acid halogens or their solutions, carboxylic acids are formed.
9 Write equations for the transformations below indicating conditions and catalysts.
a. n – pentanoic acid from n – pentanol b. 1,5 – pentanedioic acid from cyclopentene c. Benzoic acid from chlorobenzene d. 1,4 – hexandioic acid from 1,4 – dibromobutane e. Formic acid from ethyl formate Carboxylic Acids
125
6. SOME COMMON CARBOXYLIC ACIDS 6.1. FORMIC ACID Formic acid is the simplest carboxylic acid (HCOOH). In nature, it is found in the stings and bites of many insects, including bees and ants. The name “formic” is derived from the Latin name for ant, formica.
Physical Properties Formic acid is miscible with water and slightly soluble in hydrocarbons. It dissociates into ions in aqueous solution: HCOOH(aq) Ants have formic acid.
HCOO–(aq) + H +(aq)
Ka = 1.8 · 10–4
It is a colorless, pungent, fuming and corrosive liquid with a boiling point of 100.5°C.
Chemical Properties The strongest monocarboxylic acid is formic acid.
If the structure of formic acid is examined, it is seen t o contain both an aldehyde and a carboxyl group. For this reason, unlike other organic acids, formic acid and its salts can be oxidized. When it is oxidized, it first produces carbonic acid (an unstable intermediate) and then carbon dioxide and water.
126
Oxygen And Nitrogen Containing Organic Compounds
As formic acid contains the aldehyde group it reacts with Fehling’s and Tollens’
The stings of bees contain formic acid. A bee sting should be treated with dilute ammonia solution.
reagents.
When formic acid is heated it decomposes into CO and H 2O, though if H 2SO4 is used as a catalyst, the reaction occurs at a lower temperature. heat
HCOOH
CO + H2O
10 How many grams of pure formic acid must be used to precipitate 6.48 grams of silver upon reaction with an excess amount of Tollens’ reagent? (HCOOH : 46 g/mol, Ag : 108 g/mol)
Formic acid reaction with Tollens’ reagent; HCOOH + 2Ag + + 2OH– 46 g formic acid
2Ag + CO2 + 2H2O (2 . 108) g Ag
x g formic acid 6.48 g Ag ————————————————————————— x = 1.38 g formic acid is used
Production The most widely used methods to produce formic acid are from the oxidations of methanol and formaldehyde. Bees secrete formic acid. Carboxylic Acids
127
1. In industry, the sodium salt of formic acid is produced from the reaction of CO and NaOH under high pressure and temperature. This salt is then reacted with H2SO4 and H3PO4, to produce formic acid. CO + NaOH
200 °C, 10atm
HCOONa sodium formate
200 °C, 10atm
HCOONa + H2SO4
H
sodium formate
COOH + NaHSO4
formic acid
2. In the laboratory formic acid can be produced by heating an aqueous solution of oxalic acid in the presence of glycerine.
Uses Formic acid, like formaldehyde, has good disinfectant properties. It exists
in honey preventing it from being spoilt easily. It is also used in textile dying and leather tanning. In addition, formic acid is a starting material in the production of fertilizers, rubbers and plastics. Plus the calcium salt of formic acid is a good softener when dissolved in water.
Production of formic acid in the laboratory
6.2. ACETIC ACID Acetic acid an important carboxylic acid. It is found in vinegar at a concentration of around 4-6%. It has the characteristic odor and taste of vinegar and in fact, the name acetic acid is derived from “acetum” meaning vinegar in Latin. Pure acetic acid solidifies at 16.7 °C and takes on an ice-like appearance. For this reason solid acetic acid is also known as glacial ethanoic acid.
Physical Properties Pure acetic acid is a colorless, crystalline compound that melts at 16.7°C and its boils at 118°C. It is miscible with water but its ionization percentage is very low, about 3%. CH3COOH(aq)
CH3COO–(aq) + H +(aq)
Ka = 1.8 . 10–5
Chemical Properties Acetic acid shows all the characteristic properties of carboxylic acids. Hydrogen gas and acetate salts are formed upon reaction with metals and it undergoes neutralization reactions with bases and basic salts.
128
Oxygen And Nitrogen Containing Organic Compounds
Production 1. Acetic acid can be produced by the enzyme-catalyzed oxidation of ethyl alcohol. The brown acetic acid in vinegar is produced from fruit juices (apple or grape juice) and is known as natural acetic acid.
2. Acetic acid, unlike formic acid, cannot be oxidized easily. Thus, acetates can be reacted with H2SO4 to produce acetic acid. As mentioned earlier, acetate produced by the condensation of wood can be precipitated as calcium acetate using limewater. Methanol and acetone are evaporated from the mixture and if the remaining calcium acetate is reacted with H 2SO4, 99.5% pure
Acetic acid reacts with egg shells to produce CO2.
acetic acid is obtained.
3. In industry, the aldehyde formed by addition of water to acetylene is oxidized
to produce acetic acid.
11
Production of acetic acid from calcium acetate
How many liters of H 2 gas at STP would evolve from the reaction of 150 grams of 18% acetic acid solution with excess magnesium? (CH3COOH : 60 g/mol, Mg: 24 g/mol)
Mass of pure acetic acid m = 150 g (18/100) = 27 g Mole number; m 27 g n = –––––– = ––––––––––– = 0.45 mol M 60 g/mol The reaction equation of acetic acid with Mg; 2CH3COOH + Mg (CH3COO)2 Mg + H2 0.45 mol
0.225 mol
V H = 0.225 mol · 22.4 L/mol = 5.04 L 2
Carboxylic Acids
129
Uses Acetic acid is used as a solvent for resins and oil. Its salts are as important as the acid itself. For example, methane is produced from sodium acetate and acetone is produced from calcium acetate. Aluminium acetate is used in dyeing as a mordant, for proofing paper and fabrics and in pharmacy as an antiseptic and astringent. Cellulose acetate, an acetic acid derivative, is used in lacquers, shatter- proof glass, varnishes and as a fiber. Acetic acid is also the starting material in the production of rubber.
C
A
A
T
P
Carboxylic acids that contain a double bond in their structure are called unsaturated carboxylic acids. Examples of these acids are propenoic acid, 2–methylpropenoic acid, trans-2-butenoic acid, cis-2-butenoic acid.
ACRYLIC ACID (Propenoic acid, vinyl formic acid)
Acrylic acid and its fumes have a pungent, unpleasant odor and are a strong irritant. It is miscible with water, alcohol, chloroform and ether. It polymerizes easily in the presence of oxygen and has a boiling point of 141°C. Acrylic acid is obtained from the oxidation of allyl alcohol or acrylaldehyde.
Orlon is used for producing carpets and clothing.
When it is heated, a glacial resin is produced.
130
Oxygen And Nitrogen Containing Organic Compounds
Acrylonitrile polymerizes to form polyacrylonitrile or orlon (acrilan).
Acrylonitrile is produced by the addition of HCN to acetylene
META ACRYLIC ACID Its IUPAC name is 2-methylpropenoic acid and it is well known from its reaction with methyl alcohol to produce the ester, methyl methacrylate.
Acrylic paints contain a co-polymer of methyl methaacrylate, They are rather expensive but highly resist ant to water.
Methyl methacrylate forms a polymer, a colorless liquid insoluble in water and glass-like, that is used in manufacturing contact lenses and shatterproof glass.
Polymers of methyl methaacrylate are used in manufacturing highly transparent and resistant contact lenses.
Polymers of methyl methaacrylate are also used in the manufacture of shatterproof security glass.
Carboxylic Acids
131
7. DICARBOXYILIC ACIDS These are compounds with two carboxyl (–COOH) groups in their structure. Their general formula is HOOC – (CH2)n – COOH. All dicarboxylic acids have common names.
Tomatoes are vegetables that contain oxalic acid and its salts.
Some dicarboxylic acids are important monomers used in synthesizing polymers. For example, adipic acid (COOH(CH 2)4COOH) is used for synthesizing nylon. In dicarboxylic acids, ionization of the second carboxyl group occurs less readily than the ionization of the first. Thus, K a values of dicarboxylic acids are bigger 1
than their Ka values. 2
7.1. OXALIC ACID This occurs as a free acid in beet leaves, sorrel, spinach, asparagus, tobacco, and tomatoes. Its name comes from Latin “oxolis” which means “sorrel” one of the acid's primary sources.
Physical Properties Oxalic acid is a white, crystalline solid. Its melting point is 189 °C though it subOxalic acid occurs in the leaf blades of rhubarb. Pure oxalic acid is a white crystalline solid.
limes at 157 °C. It is poisonous, the calcium salt of oxalic acid precipitates in the kidneys. Oxalic acid is the strongest of the dicarboxylic acids.
Chemical Properties When it is heated with glycerine, oxalic acid decomposes into formic acid and carbon dioxide.
Oxalic acid is a reducing agent, and can be easily oxidized by acidified KMnO 4.
132
Oxygen And Nitrogen Containing Organic Compounds
Production 1. Oxalic acid is made from its sodium salt, and this in turn is obtained from heating sodium formate.
Oxalic acid salts can be obtained from some plants, such as asparagus.
Oxalic acid salts can be obtained directly from some plants. They can also be obtained by passing CO2 through Na or K at 300-350°C and high pressure.
2. Oxidation of glycol results in oxalic acid. This process must be carried under controlled conditions as the reaction may continue and form carbon dioxide.
Uses Because of its reducing properties, oxalic acid is used to bleach wood cellulose, hay and feathers. It is also used in the manufacture of ink.
7.2. MALONIC ACID This was first obtained from the oxidation of malic acid (apple acid) and takes its name from this. It occurs in the mixed calcium salts obtained during the process-
ing of sugar beet.
It is a colourless liquid that boils at 136 °C. It dissolves in both water and alcohol
and decomposes into acetic acid above 140 °C.
Malonic acid undergoes all the characteristic reactions of dicarboxylic acids. Its esters are used in organic synthesis. Malonic acid can be obtained from the hydrolysis of cyanoacetic acid.
Carboxylic Acids
133
7.3. ADIPIC ACID Its name comes from “adeps”, meaning “oil” in Latin, due to the fact adipic acid was first obtained from oils. When it is heated it forms cyclopentanone.
Manufacture of nylon.
Adipic acid is a solid with a melting point of 153 °C. It is produced from the oxidation of cyclohexanol with a nitric acid catalyst.
If forms long chain polymers upon reaction with diamines and is largely used in the manufacture of nylon.
Hexamethylene diamine is dissolved in water (bottom layer) and adipic chloride is dissolved in hexane (upper layer). Nylon is formed between these two layers
8. FATTY ACIDS Fatty acids are long chained carboxylic acids. Most of the carboxylic acids in the fatty acids fraction are found as esters of glycerol. The simplest member of the fatty acids is butyric acid, this has four carbon atoms. (C 3H7COOH). Fatty acids can be classified as saturated or unsaturated.
134
Oxygen And Nitrogen Containing Organic Compounds
8.1. SATURATED FATTY ACIDS Palmitic Acid (C15H31COOH) This is a white crystalline solid with a melting point of 63 °C. It occurs in palm oil, beeswax and other animal and vegetable fats and oils. It is insoluble in water but soluble in alcohol and ether.
Stearic Acid (C 17H35COOH) This is a crystalline solid with a melting point of 70 °C. It is soluble in ether and hot alcohol. Stearic acid is one of the most common fatty acids and
Candles are a mixture of occurs in the form of glycerides in most animal and stearic acid and palmitic vegetable fats. A solid mixture of stearic and acid. palmitic acid is used to make candles.
The simplest member of the fatty acids is butyric acid.
8.2. UNSATURATED FATTY ACIDS Fatty acids which contain a carbon-carbon double bond on the chain attached to the carboxyl group are called unsaturated fatty acids.
Oleic Acid (C17H33COOH) This generally occurs in the form of glycerides in olive, almond, cotton and sunflower oils. Oleic acid is a colorless, tasteless and odorless liquid with a melting
Coconuts contain palmitic acid.
point of 13 °C. It forms one third of the total fatty acids in cow’s milk and is used in the production of lubricants, detergents, resins and other products. Stearic acid is formed by the addition of hydrogen to oleic acid.
Linoleic Acid (C17H31COOH) and Linolenic Acid (C17H29COOH) These two acids occur widely in the form of glycerides in vegetable oils such as linseed, sesame and poppy oils. Linoleic acid has two double bonds within the alkyl chain, where linolenic acid has three. CH3(CH2)4 CH = CHCH2CH = CH (CH 2)7 COOH linoleic acid
Almond oil contains oleic acid.
CH3CH2CH = CH CH 2CH = CH CH2CH = CH (CH 2)7COOH linolenic acid
In saturated fatty acids, the alkyl chains are aligned in a zig-zag shape due to the tetrahedral geometry surrounding the carbon atoms. This structure spreads out the molecules, keeping van der Waals forces at a maximum.
Carboxylic Acids
135
To test if a fat contains unsaturated fatty acids it is dipped into an erlenmayer flask filled with bromine gas. If the bromine color disappears, the fat contains unsatu rated fatty acids.
In unsaturated fatty acids, the (C=C) atoms enter this zig-zag shape with a 120°C geometry, causing the molecules to form a spiral structure. Naturally occuring fatty acids have a cis geometry. This cis-structure decreases the melting points of the acids and hence increasing the number of double bonds in unsaturated fatty acids decreases the melting point.
9. OXYACIDS Organic acids with a hydroxy group(–OH) in addition to the carboxyl group are called oxyacids or hydroxy acids. The –OH functional group in oxyacids gives the compound alcohol properties. Most oxyacids occur in plants and fruits. They may also contain more than one hydroxy group (–OH).
Fruits contain oxyacids.
136
Oxygen And Nitrogen Containing Organic Compounds
Oxyacids form strong hydrogen bonds with water since they have both hydroxy
(–OH) and carboxyl (–CO2H) groups. Thus, they are highly soluble in water.
Production
–hydroxy acids can be obtained by t he hydrolysis of nitriles starting from the rel-
evant aldehyde or ketone.
Citric acid (lemon acid)
Carbonic Acid Carbonic acid is the simplest member of the hydroxy acids. It is classified as an inorganic acid because of its carbonate and bicarbonate salts. However, it may
Tartaric acid (grape acid)
also be considered an organic acid as it contains both the hydroxy and carboxyl groups.
Carbonic acid can not be isolated and is formed only in aqueous solution by dissolving CO2 gas in H2O. It is a very unstable compound and is easily ionized to –
H+ and HCO3 ions in water. CO2(g) + H 2O(l)
H2CO3(aq)
H+(aq) + HCO 2–(aq) 3
All kind of fizzy drinks (cola, mineral water, etc.) contain carbonic acid. Under lowered pressures carbonic acid decomposes to CO 2 and H2O.
Malic acid (apple acid) Carboxylic Acids
137
10. OPTICAL ISOMERISM From common experience we know that a right hand glove doesn’t fit on a left hand and vice-versa. This is because our right and left hands are not identical but mirror-images of each other; they are non-superimposable. Molecules that have nonsuperimposable mirror images are called chiral. In our daily life we encounter many different examples of chirality; our feet, spiral shells and screws. Most bio molecules in plants and animals are chiral molecules. They exist in nature as a single type of chiral molecule (either the left or right hand image). For example, 20 naturally occuring amino acids exist in nature and all of these molecules are the left hand type. Natural sugar molecules exist as the right hand type. A chiral molecule and its non-superimposable image are called enantiomers. So The mirror image of a left hand is a right hand.
isomers that are mirror images of each other are enantiomers. For molecules to have enantiomers, their structure must be asymmetrical. The simplest asymmetrical molecule is the tetrahedrally bonded carbon atom with four different types of atoms or groups attached to it. These kinds of carbon atoms are called asymmetric or chiral carbon atoms and the molecules are called chiral molecules. Some compounds may occur in nature with both enantiomers present. For example, lactic acid can be found in nature this way.
c. a.
b.
Enantiomers of lactic acid: a. –OH, –CH3 and –COOH groups are arranged within the molecule in a clockwise direction. b. I and II isomers are mirror images of each other. c. The two isomers are not superimposable.
138
Oxygen And Nitrogen Containing Organic Compounds
Let us examine lactic acid to understand how molecules can exist as two enantiomers. The central carbon atom of lactic acid has four different atoms or groups attached to it; –H, –OH, –CH 3 and –COOH. Interchanging any two groups on the central atom converts one enantiomer to the other. When we put isomer I in front of a mirror the image seen in the mirror is the image of isomer II. However, the image and isomer I are not superimposable. Therefore, the two nonsuperimposable molecules are en antiomers of each other. Enantiomers can be represented by the letters D and L according to their geometry. If the rotation of the plane (see below) is to the right the substance is dextrorotatory (Latin: dexter, means right); if the rotation is to the left, the substance is laevorotatory (Latin: laevus, means left). For example, the enantiomer of lactic acid formed in sour milk is D-lactic acid, the other, which is found in muscles and produced in high amounts after performing heavy exercise, causing cramps, is L-lactic acid. Enantiomers of a chiral molecule have identical melting and boiling points, densities, and other physical and chemical properties. However, enantiomers show different behaviour towards plane-polarized light. When a beam of plane polarized light passes through an enantiomer, the plane of polarization rotates. For this reason chiral molecules are known as optical isomers and are said to be optically active.
“Polarized light consists of electromagnetic waves vibrating along one direction”
Enantiomers show different characteristics in te rms of their biological properties. The molecules involved in the metabolisms of animals and plants are mostly chiral molecules and the reactions of different enantiomers occur at different rates. We may think of the glove and hand analogy; although we are able to put a lefthanded glove onto a right hand, this process takes a lot of time and the glove doesn’t fit correctly. Carboxylic Acids
139
Naturally occuring amino acids are -isomers and the enzymes that react with these amino acids are also -isomers. Consequently, enzyme structures are essential in controlling the rates of reactions of enantiomers. The synthesis of chiral molecules in laboratories results in the formation of a racemic mixture, an equal percentage mixture of both enantiomers. The extraction of enantiomers from racemic mixtures is almost impossible because of the identical physical and chemical properties of the enantiomers. Racemic mixtures are optically inactive, as they contain equal amounts of the D and L isomers. Some big organic molecules may contain more than one asymmetric carbon atom in their structure. An increasing number of asymmetric carbon atoms (n) increases the number of enantiomers by a factor of 2 n. For example glucose contains 4 different asymmetric carbon atoms. Thus, glucose has 16 optical isomers (2 4), of which 8 are D, and 8 are L enantiomers.
A chiral molecule and its non-superimposable image are called enantiomers.
140
Oxygen And Nitrogen Containing Organic Compounds
12 How many asymmetric carbon atoms do the molecules below contain?
a, e and f have one asymmetric carbon atom (shown by *, sign) each, and the others don’t have any. An asymmetric carbon is determined by examining each group bonded to the atom. The carbon atom must have four bonds and all the groups or atoms attached to it must be different.
Carboxylic Acids
141
1.
What is the general structure of a carboxylic acid? What are the differences between carboxyl compounds and aldehydes and ketones?
7.
Write the names and formulae of all isomers of the carboxylic acid with the general formula C5H10O2.
2.
Is there any difference between the term “carboxylic acid” and “organic acid”? Explain.
8.
Name the following compounds using both the IUPAC system and their common names.
3.
Which of the following compounds are carboxylic acids?
4.
5.
Give the approximate values of angles a, b, c and d between the bonds in acetic acid?
A monocarboxylic acid contains 55.8% C, 7% H and 37.2% O by mass. What is the molecular formula of this compound? (C: 12 g/mol, O: 16 g/mol, H: 1 g/mol)
9.
Name the following carboxylic acids using the IUPAC system.
6.
Classify the following carboxylic acids according to both the number of their carboxyl groups and their functional groups.
142
Oxygen And Nitrogen Containing Organic Compounds
10. Write out the molecular formulae of the carboxylic acids below.
15. Show the hydrogen bonds formed between two acetic acid molecules
a. 2-oxypropanoic acid b. 2,3-dimethylbutanoic acid c. 3-amino-4-bromopentanoic acid 16.
d. 3-hydroxy-4-methylhexanoic acid e. cis-2-butenoic acid
III. CH3CH2CH3
g. -chlorovaleric acid
Compare the above molecules according to their solubility in water.
h. cis-2-valeric acid
-hydroxybutyric acid
i.
CHCH3
II. HCOOH
o-methylbenzoic acid
f.
I. CH3CH
2-methyl-1,4-butanedioic acid
j.
17. Compare
11. Give the common names of the following acids.
the
solubility
of
C17H35COOH
and
C17H35COONa in;
a. Ethanoic acid b. Ethandioic acid
a. Water
c. Butanoic acid
b. Ether
d. Pentanoic acid
18. Explain the reasons for the large differences between the boiling points of the given compounds despite their similar molecular masses?
12. Give the IUPAC names of following acids. a. Oxalic acid b. -oxyvaleric acid
Compound
Molar Mass (g/mol) ——————— ————————— ethyl alcohol 46
c. Adipic acid d. Malonic acid
13. Explain why carboxylic acids dissolve in water better than alcohols.
14. Which of the following represents a hydrogen bond formed by the dissociation of a carboxylic acid in water? Explain.
46
–25
propane
44
–42
formic acid
46
100.5
19. Write out the ionization reaction of acetic acid in water and show the conjugate acid-base pairs.
diethyl ether
Boiling Point (°C) ——————— 78
20. Does hexanoic acid or sodium hexanoate dissolve better in water? Explain.
21. Which has the highest boiling point, acetic acid or potassium acetate? Explain. Carboxylic Acids
143
22. Acetic acid, also known as vinegar acid, has a specific odor. A 3% by mass solution of sodium acetate solution has almost the same odor as acetic acid. Explain.
29. Classify the following compounds according to their functional groups.
23. The hydrogen ion concentration of a 400 mL solution containing 0.2 mole of a monocarboxylic acid is 3 . 10–3 M. Using this information,
a. Find ionization percentage of this acid. b. What is the Ka value of this acid? 30. If 0.1 mole of HCl is added to a 1 liter of solution of 0.1 M CH3COO–, how many mole of H + ions will be there 24. What is the pOH value of a 0.01 M 2-methylpropanoic acid solution? (Ka = 1.6 . 10–5)
25. How many moles of 2-chloroacetic acid are there in 5 liters of a solution with a pH value of 2? (Ka = 1.4 · 10–3)
in the solution? (ignore volume change after mixing)
31. Draw the molecular structures of the esters that are formed after the reaction between ethyl alcohol and: a. Acetic acid b. Isobutyric acid c. p-methylbenzoic acid d. Oxalic acid
26. What is the molarity of a 50 ml tartaric acid solution of which 250 ml of 0.01 M NaOH is required to neutralize it?
32. Complete the reactions below 27. Determine A, B, C and D. CH2
CH2 + HBr
A
C2H5OH
B
A + KCN
heat
C
B + HCl
H2 O
C + PCl5
C2H5OH
D
[O]
a. (CH3)2CHCH2OH b. C2H5COOH + Zn c. HCOOH + CaCO3 H+
d. C2H5COOH + C3H7COOH e. C3H7COOH + SOCl2 f.
P
(CH3)2CHCOOH + Cl2 COOH
28.
144
Oxygen And Nitrogen Containing Organic Compounds
COOH
Which compound is produced from the reaction of the above compound with NaOH?
+K
g. COOH
h. COOH
+ Ba(OH)2
33. Write out the reactions of acetic acid with the reagents given below. a. Ba
b. Mg(OH)2
d. CaCO3
e. C2H5OH / H+ f. SOCl2
g. PCl3
h. PCl5
38. Starting from n-butyl chloride, obtain pentanoic acid.
c. KHCO3
i. Cl2 /P
39. Starting from ethyl alcohol, show how the following two acids could be produced; a. Ethanoic acid b. Propanoic acid
34. Write out the reactions of benzoic acid with the given reagents.
Show all steps of the reactions.
a. Na b. Ca c. CH 3OH d. Br 2 /P e. PCl 5 f. SOCl 2
40. Complete the following reactions. 35. What is the molecular formula of the magnesium s alt of a carboxylic acid that contains 9.03% Mg, 63.16% C, 3.76% H and 24.06% O by mass? (Mg : 24 g/mol, C : 12 g/mol, H : 1 g/mol, O : 16 g/mol)
36. Write the names of carboxylic acid derivatives given below. a. CH3COCl
b. CH3CH2COOCH3
c. (CH3COO)2Ca
d. (HCOO)2 Mg
e. CH3CONO2
f.
Ca(HCOO)2
41. Write out and complete the reactions given below. a. benzoyl chloride + sodium hydroxide b. acetyl propionate + potassium hydroxide c. sodium acetate + hydrogen bromide
37. Write molecular formulae of given compounds. a. Propanoyl chloride
d. formic acid + phosphorous pentachloride
b. Sodium benzoate c. Ethyl butyrate d. Magnesium oxalate e. Sodium acetate f.
Calcium glycolate
42. How can formic acid be separated from a mixture of formic acid and water? (b.p. of formic acid : 100.5°C and b.p. of water : 100°C)
g. Dichloroacetic acid h. Zinc stearate i. Acetic acid anhydride j.
Potassium ethanoate
k. Calcium oxalate l.
Potassium acrylate
43. Formic acid undergoes a reaction with Fehling’s solution whereas acetic acid and propanedioic acid do not. Explain. Carboxylic Acids
145
44. Complete and balance the reactions below.
51. 160 grams of a 20% by mass NaOH solution is used to neutralize 41 grams of a formic acid - acetic acid mixture. How many moles of acetic acid are present in this mixture?
a. HCOOH + Ag+ + OH – H2SO4
b. HCOOH Cu, Ni
c. HCOOH d. HCOOH + KMnO4 + H 2SO4 52. How many milliliters of CO2 at STP are produced by 45. How many grams of 40% by mass formic acid solution must be used to precipitate 32.4 grams of Ag from an excess of Tollens’ reagent?
46. How many grams of Cu2O can be precipitated from the reaction of 150 grams of a 23% by mass solution of formic acid with an excess amount of Fehling's solution? (Cu : 63.5 g/mol, O : 16 g/mol)
pouring 120 grams of 7% by mass vinegar acid onto a bench made of marble?
53. Write a. The molecular formula, b. The IUPAC name of oxalic acid.
47. Crystalline acetic acid melts below its given melting point when kept in air. Why? 54. What are fatty acids? Why are they called fatty acids? Explain. 48. For acetic acid (Ka = 1.8 · 10–5) a. What is the percentage ionization of a 0.2 tion?
M
solu-
b. What is the pH ratio of a 0.2 M solution to a 1.0 solution?
M
49. 5.6 L of H2 at STP is produced by the reaction of Zn metal with a 25% by mass CH3COOH solution with a
55. Which of the following c ompounds are fatty acids? a. CH3COOH
b. C2H5COOH
c. C3H7COOH
d. C15H31COOH
e. C15C29COOH
f.
C12H25COOH
density of 1.035 g/mL. What is the volume of this solution? (CH3COOH : 60 g/mol)
56. For tartaric acid (grape acid), give 50. For 220 g of a formic acid-acetic acid - water mixture I. 42.56 L H2 at STP is produced by the reaction with an excess amount of Mg
a. Its molecular formula b. The functional groups within the molecule c. Its neutralization reaction with NaOH
II. 216 g of Ag is precipitated by the reaction with an excess of Tollens' reagent what is the mass of w ater in the mixture? (C : 12 g/mol, H : 1 g/mol, O : 16 g/mol) 146
Oxygen And Nitrogen Containing Organic Compounds
57. Give the sources of fatty acids.
1.
What is the molecular formula of the carboxylic acid that contains 40.68% C, 54.24 % O and 5.06 % H by mass?
4.
2 methyl, 1 carboxyl and 1 hydroxy group are attached to a carbon atom. What is the correct name of this com-
(C : 12 g/mol, H : 1 g/mol, O : 16 g/mol)
pound?
A) HCOOH
A) 2,2-dimethyl-2-hydroxyethanoic acid
B) CH3COOH
B) 2-hydroxy-2-methylpropanoic acid C)
C) 1-methyl-1-hydroxybutanoic acid
D) HOOC(CH2)2COOH
D) Isopropionic acid
E) 2-hydroxy-3-methylpropanoic acid
E) C6H5OH
2.
Which one of the given compounds is a ketoacid?
5.
3.
HCOOH(l)
HCOO–(aq) + H+(aq)
What is the pH of a 10–2
M
A) 2
C) 4
B) 3
Ka = 10 –4
HCOOH solution? D) 5
E) 6
What is the correct name of the above c ompound? A) 1,2-dihydroxy-3-amino-4-methylpentanol B) 2-hydroxy-3-amino-4-methylpentanoic acid C) 1-hydroxy-2-amino-3-methylbutanoic acid D) 1,2-dihydroxy-3-amino-4-methylpentanoic acid E) 2-hydroxy-3-amino-4-methylpentanol
6.
Which of the compounds below has the highest boiling point? A) CH3CH2CH2CH3 B) CH3COOH C) CH3CH2OH D) HOOC E) CH3CH2
CH2CH2 O
COOH
CH3 Carboxylic Acids
147
7.
10. What is the molar mass of the aldehyde that is produced
by the one-step reduction of a monocarboxylic acid with a
molar mass of 74 grams?
(C : 12 g/mol, H : 1 g/mol, O : 16 g/mol) A) 46
B) 58
C) 62
D) 66
E) 72
What is the correct order of boiling points for the above compounds? A) I > II > III > IV
B) IV > III > II >I
C) I > II = III > IV
D) IV = III = II >I E) IV > II = III > I
11.
8.
1 mol of this compound;
According to above reaction, how many grams of NaOH would react with 90 grams of a 20% by mass oxalic acid solution?
I. reacts with 2 mol Na
(C: 12 g/mol, H: 1 g/mol, O: 16 g/mol, Na: 23 g/mol)
II. reacts with 1 mol NaOH
A) 4
III. reacts with 1 mol Zn
B) 8
C) 16
D) 20
E) 40
which of the above are correct? A) I only
B) III only D) II and III
9.
C) I and II E) I, II and III
12. Which one of the following compounds does not show
reacts with;
acidic properties?
I. ammoniacal AgNO3 II. NaOH
III. hydrogen
which of the above is/are correct? A) I only
B) II only D) II and III
148
C) I and II E) I, II and III
Oxygen And Nitrogen Containing Organic Compounds
13. Which one of the following c ompounds is produced by the two degree reduction of formic acid? A) Methanoic acid
B) Meth anal
D) Formaldehyde
16.
I. C2H5OH + CH3OH
C2H5OCH3 + H2O
II. CH3OH + CH3COOH III. KOH + HCOOH
C) Methanol
E) Ethyl alcohol
CH3COOCH3 + H2O
HCOOK + H2O
Which of the above reactions are esterification reactions? A) I only
B) II only D) II and III
17.
14. Regarding
II. when it is oxidized, an ether is formed.
III. it is an acid anhydride. Which of the above statements is/are incorrect?
D) II and III
,
B) II only
E) I, II and III
I. it is a dicarboxylic acid.
A) I only
C) I and II
Which of the above compounds show both acid and
C) I and III
aldehyde properties? A) I only
E) I, II and III
B) III only D) II and III
C) I and II E) I, II and III
18. Which one of the following is the product of the reaction between dilute H2SO4 and formic acid? 15. What is the molar mass of the ester that is produced from the reaction of 60 grams of a carboxylic acid with 46 grams of an alcohol? A) 106
B) 88
C) 98
D) 124
E) 82
Carboxylic Acids
149
19. Which one of the following compounds cannot be oxi-
23.
dized to a carboxylic acid? A) Methanol
II. Lactic acid
B) Ethanol
D) n-propanol
I. Acetic acid
III. Oxalic acid
C) Butanol
Which of the above repr esent a hydroxy acid?
E) 2-pentanol A) I only
B) II only D) II and III
C) III only E) I, II and III
20. Which one of the following carboxylic acids cannot be obtained by the reaction of a Grignard compound with CO2? A) HCOO H
B) CH3COOH
D) C 3H6COOH
C) C2H5COOH
E) C4H10COOH
24. Some common acids found in daily life together with their sources are given below, I. lemon salt: citric acid II. aspirin: acetyl salicylic acid III. vinegar: acetic acid
21. 134.4 mL CO2 at STP is obtained from the reaction of 6
Which pairings are correct?
grams vinegar with an excess of NaHCO3. What is the
A) I only
mass percentage of acetic acid in the vinegar?
B) I and II D) I and III
C) II and III E ) I, II and III
(CH3COOH : 60 g/mol) A) 4.5
B) 6.0
C) 9.6
D) 21
E) 45
22. Large molecules of saturated monocarboxylic acids are solid at room temperature. I. C17H35 COOH
25.
The compound above,
II. C15H31COOH
I. is optically active II. contains four asymmetric carbon atoms
III. C17H33 COOH Which of the above compounds are solid at room con-
III. contains aldehyde, alcohol and carboxyl groups
ditions?
Which of the above are correct?
A) I only D) II and III 150
B) III only
C) I and II E) I, II and III
Oxygen And Nitrogen Containing Organic Compounds
A) I only D) II and III
B) II only
C) I and III E) I, II and III
26.
28.
Regarding above compound,
Which of the above statements are correct? B) II only D) I and III
How many asymmetric carbon atoms does this compound have?
III. H2 gas is evolved upon reaction with Mg
A) I only
I. it reacts with KOH II. it is optically active
A) 0
B) 1
C) 2
D) 3
E) 4
C) I and II E ) I, II and III
29.
27. In digital clocks, a liquid crystal substance which is
The above compound,
I. resistant to acids and bases
I. has 2 asymmetric carbon atoms.
II. optically active
II. is optically active.
is needed.
III. has 2 optical isomers.
Which one of compounds below satisfies these two con-
Which of the above s tatements is(are) w rong?
ditions? A) I only
B) III only D) II and III
C) I and II E) I, II and III
30.
I. Naturally occurring fatty acids exist in the cis-geometry. II. The simplest fatty acid is butyric acid, C3H7COOH.
III. Double bonds in the structure decreases the melting points of fatty acids. Which of the above st atements is(are) true ?
A) I only
B) II only D) II and III
C) I and III E) I, II and III
Carboxylic Acids
151
D w G
h T
b
j t
u ( l
n
a n l t t r
P m c
c u t
h b t f i t
l S
L a
P t c M
152
Oxygen And Nitrogen Containing Organic Compounds
i t
s
INTRODUCTION The reaction between an acid and a base is called neutralization and the products are salt and water. The parallel reaction between a carboxylic acid and an
Esterification
alcohol is called esterification and the products are an ester and water.
To identify the bond breakages in esterification, an alcohol containing the 18O isotope is used. After esterification it is seen that the 18O isotope appears in the ester. This result reveals that the water is formed from the hydroxyl group of the acid and the hydrogen of the alcohol. In other words the OR group from the alcohol molecule replaces the OH group of the acid molecule.
Neutralization and esterification reactions are similar in terms of the functional groups of the reactants and products. The main differences between these two reactions are that esterification reactions are slow, reversible and don’t take place between ions.
1. ESTERS
Esters are derivatives of carboxylic acids formed by replacing the hydroxyl (
OH) group by an alkoxy (
OR) group. They can be defined as alkyl salts
of carboxylic acids and are represented by the general formula RCOOR .
The functional group of esters,
, is bonded to two alkyl groups,
except for formates, which have a hydrogen atom bonded to the carbon atom of the functional group.
2. NOMENCLATURE OF ESTERS The nomenclature of esters is similar to the nomenclature of the carboxylic acid salts. The alkyl group bonded to the oxygen atom is named first, then the –ic acid ending of the corresponding carboxylic acid is changed to –oate.
154
Oxygen And Nitrogen Containing Organic Compounds
Common Name
IUPAC Name
Acid halide
Alkanoyl halide
Acid anhydride
Alkanoic anhydride
Formula
Ester
Alkanoate
Amide
Alkanamide
Table 1: Some carboxylic acid derivatives
Common Naming The "ester" suffix is added to the end of alkyl groups found in an ester. The alkyl name from the alkoxy group is put first.
1 Name of the following compounds:
a. Isopropyl ethanoate b. Ethyl dichloroethanoate c. Benzyl methanoate d. t – butyl – p – chlorobenzoate Esters
155
2 Write the structural formulae for the following esters.
a. Isobutyl acetate
b. Ethyl benzoate
c. t–butyl formate
d. p–chlorophenyl–2–methyl butanoate
e. Ethyl bromoethanoate
f. Sodium ethanoate
g. Ethyl propanoate
h. Benzyl acetate
3. PHYSICAL PROPERTIES OF ESTERS Esters with small chained alkyl groups are colorless liquids with pleasant odors. They are obtained from natural sources such as plants, flowers and fruits and are what give them their pleasant smells. So, for example, the smells of mint and thyme are due to esters in their structures. Natural fruit aromas are mixtures of certain organic compounds and esters. Synthetic aromas prepared in laboratories are simple mixtures of these same est ers and organic compounds. They are used in perfumes, foods and drinks to give taste and pleasant smells. Ethyl acetate, for example, is a colorless liquid with an apple flavour; it is known as apple ester and is used in perfumery as a fruit essence. Propyl acetate has the smell of pears, isopentyl acetate that of bananas and ethyl butyrate smells of pineapples. All are colorless liquids. Higher molar mass esters are odorless. 156
Oxygen And Nitrogen Containing Organic Compounds
Name
Structure
Odor
Isobutyl formate
HCOOCH2CH(CH3)2
Raspberry
Ethyl acetate
CH3COOC2H5
Apple
Propyl acetate
CH3COOC3H7
Pear
Ethyl butyrate
C3H7COOC2H5
Pineapple
Isopentyl acetate
CH3COOC5H11
Banana
Methyl salicylate
HOC6H4COOCH3
Wintergreen
n – pentyl butyrate
C3H7COOC5H9
Apricot
n – octyl acetate
CH3COOC8H17
Orange
Table 2: How esters smell.
The smell of pineapple is due to ethyl butanoate in its structure.
Esters do not have hydrogen bonding between their molecules and therefore they have lower boiling points than carboxylic acids of th e same molar mass. Low molar mass esters are liquids with low boiling points. Higher molar mass esters (fats and waxes) are solids or liquids with a high density. Lower molar mass esters form hydrogen bonds with water but as the length of their alkyl groups increase, their solubility in water decreases. Esters which are insoluble in water are soluble in alcohol and ether. Esters have lower densities than water. Liquid esters are good organic solvents, for example, nitrocellulose is used to dissolve some natural and synthetic resins and plastics.
Name
Chemical Formula
Melting Point (°C)
Isopenthyl acetate gives bananas their pleasant smell.
Boiling Point (°C)
Solubility (g/100 mL water)
Methyl formate
HCO2CH3
– 99
31.5
30 (very soluble)
Ethyl formate
HCO2CH2CH3
– 79
54
10.5
Methyl acetate
CH3CO2CH3
– 99
57
24.40
Ethyl acetate
CH3CO2CH2CH3
– 84
77
7.90 (25°C)
Propyl acetate
CH3CO2CH2CH2CH3
– 93
102
1.89 (moderately soluble)
Butyl acetate
CH3CO2CH2(CH2)2CH3
– 74
125
1.00 (22 °C)
Ethyl propanoate
CH3CH2CO2CH2CH3
– 73
99
1.75
Ethyl butanoate
CH3(CH2)2CO2CH2CH3
– 93
120
0.51
Ethyl pentanoate
CH3(CH2)3CO2CH2CH3
– 91
145
0.22
Ethyl hexanoate
CH3(CH2)4CO2CH2CH3
– 68
168.0
0.063
Methyl benzoate
C6H5CO2CH3
– 12
199
0.15
Ethyl benzoate
C6H5CO2CH2CH3
– 35
213
0.08
Methyl salicylate
o – HOC6H4CO2CH3
–9
223
0.74 (30°)
Table 3: Physical properties of some esters Esters
157
4. CHEMICAL PROPERTIES OF ESTERS 4.1. HYDROLYSIS OF ESTERS Soap in history Soap was first known to be used in 2500 B.C. at Mesopotamia. It was also written by the Roman Emperor Julius Caesar that some tribes in ancient Egypt used soaps. Soap was produced using the same method as today, by heating soda or wood ash with fats.
An ester hydrolyzed in the presence of an acid catalyst produces a carboxylic acid and an alcohol. This hydrolysis, the reverse of esterification, is an equilibrium reaction.
In order to increase the amount of products from the hydrolysis reaction, large quantities of water are used which shift the equilibrium to the right.
4.2. SAPONIFICATION OF ESTERS When esters are heated with aqueous solutions of strong bases such as NaOH and KOH, salts of carboxylic acids are produced which are known as soaps. A side product of the saponification reaction is an alcohol. The reaction is irreversible.
4.3. REDUCTION OF ESTERS Soaps are salts formed from the reaction of bases with esters known as fats.
Esters can be reduced to alcohols in different ways. During reduction, the acyl group of an ester is reduced to a primary alcohol. The alkoxy group of an ester is bonded to hydrogen atom and so depending upon the alkyl group present, t he alkoxy group is converted to a primary, secondary or tertiary alcohol. The most important reduction techniques are the following. Esters are reduced by sodium in the presence of ethanol.
158
Oxygen And Nitrogen Containing Organic Compounds
Esters can also be reduced by the addition of hydrogen in the presence of oxides of copper and chromium known as copper chromide. Reduction can also be carried out by LiAlH 4, though this method is very expensive.
The direct reduction of a carboxylic acid to an alcohol is very difficult to c arry out, so the acid can be first esterified and then reduced to the alcohol.
4.4. REACTION WITH AMMONIA Esters can react with ammonia to form an amide and an alcohol. The acyl group of the ester bonds to the
NH2 group of ammonia to form an amide while the
alkoxy group of the ester is bonded to the
H of ammonia to form an alcohol.
3 Write out the chemical reactions of methyl acetate with the following reagents.
a. H2O
b. NaOH
c. NH3
d. H2(CuO and CuCr2O4 catalysts) Esters
159
5. PREPARATION OF ESTERS Esters can be produced synthetically for use in perfumes and synthetic flavourings.
5.1. FROM CARBOXYLIC ACID AND ALCOHOLS Carboxylic acids react with alcohols to form esters in t he presence of an acid catalyst. In the esterification reaction
OH is removed from the acid and
H
removed from the alcohol to form water. Such reactions are equilibrium reactions and are very slow.
The yield of an esterification reaction is low. There are large amounts of acid and alcohol left in the reaction mixture. The use of an excess of either the carboxylic acid or the alcohol increases the yield. The yield of an esterification reaction can Perfumes contain esters.
also be increased by removing water from the reaction mixture as is formed.
4 What is the molar mass and possible formula of the ester th at is formed from a monocarboxylic acid with molar mass 60 g/mol and a monoalcohol with molar mass 46 g/mol? (C : 12 g/mol, H : 1 g/mol, O : 16 g/mol) 160
Oxygen And Nitrogen Containing Organic Compounds
acid
+
alcohol
ester
+
water
– 1 mol
– 1 mol
+ 1 mol
+ 1 mol
60 g
46 g
x
+ 18 g
According to the law of conservation of mass: 60 + 46 = x + 18 molar mass of the ester (RCOOR ) = 88 g/mol. RCOOR = 88 g/mol R + R + 12 + 16 + 16 = 88 g R + R = 44 g So, possible R = CH3 = 15 g/mol R = C2H5 = 29 g/mol When
R : H
or
R : C3H7
or
CH3
or
C2H5
C2H5
or
CH3
If we check the molar masses of the acid and alcohol, the correct formulae of the acid and alcohol are CH 3COOH and C 2H5OH respectively. So the structural formula of ester is
5.2. FROM CARBOXYLIC ACID DERIVATIVES Acid anhydrides and acid chlorides react with alcohols to produce esters.
Esters
161
5 Write the complete reactions between the following pairs of compounds and name the products.
a. propyl alcohol – butyric acid b. acetic anhydride – allyl alcohol c. propanoyl chloride – ethyl alcohol
6. FATS Fats are esters of fatty acids and glycerine. They are also known as triglycerides. Fatty acids are long, straight chained carboxylic acids and glycerine is a trialcohol. Fats are formed by replacing the hydrogen atoms in the hydroxyl groups of glycerine with acyl groups of fatty acids.
Fat Facts Fats play an important role in nutrition. Occuring naturally in foods; fats and oils are a concentrated form of energy for the body. As well as storing energy in the body, fats are used to insulate body tissues and help transport fat soluble vitamins throughout the blood. An important role of fats is in food preparation , they enhance food flavor, add texture, make baked products tender, and conduct heat during cooking.
162
Fatty acids may form mono, di– or tri– glycerides with glycerine as, one or two of the –OH groups in glycerine may not react with the fatty acid.
Oxygen And Nitrogen Containing Organic Compounds
If the connecting fatty acids to glycerine are all the same, the glyceride known as simple, if the acids are different, it is known as complex .
Pure fats consist of around 95% by mass triglyceride. The remaining 5% consists of mono and diglycerides, glycerine, some free fatty acids, vitamins dissolved in the fat, and minerals that give color and taste. Thus fats do not have a fixed melting point.
6.1. CLASSIFICATION OF FATS Vegetable fats: These are largely stored in the seeds of vegetables. Olive, corn, cotton, sunflower, soybean, sesame, peanut, hazelnut, dates, almonds and coconuts are the main sources of vegetable oils.
Animal fats:
Cholesterol Is cholesterol dangerous for our body, is it good or bad for us? Chemically a lipid, cholesterol is an important constituent of body cells. This fatty substance, produced mostly in the liver, is involved in salt formation and in the transport of fats in the blood stream to tissues throughout the body. Every cell of the body contains cholesterol, it is a waxy, fat-like substance. In the body cholesterol carries out many important functions such as strengthening cell membranes, helping digest fats and making hormones. On the other hand, high levels of cholesterol can be dangerous for the body. When level of blood cholesterol rises, it can build up on artery walls increasing the risk of blood clots, heart attacks and strokes.
Sheep, cow and fish are the main source of animal fats. Suet and fish oil are the most common animal fats. They may be either solid or liquid, the same as vegetable fats.
According to Their Physical State Fats and oils, since they are mixtures, may be solid, liquid or halfway in between depending upon the amount of glycerides they contain. For example, suet which contains a high amount of tri–stearine is solid, but olive oil which contains a high amount of glycerine is liquid. Butter and margarine are half–solid as they are mixtures of both solid and liquid glycerides. Some fatty acids are solid due to saturation. An example is coconut oil which is solid because it contains mainly tripalmitin and tristearine glycerides. Palmitic acid and stearic acid are saturated carboxylic acids.
Olive oil is one of the most important vegetable oils
Corn, a very important source of oil. Esters
163
Some of examples oil with their sources.
If the fatty acids that form the fats and oils are unsaturated, the fats tend to be liquids. Liquid oils are unsaturated, the number of double bonds in the fatty acids decreases the freezing point of the fat or oil.
7. HYDROGENATION AND MARGARINES As stated above, an oil is unsaturated if the fatty acids contain double bonds. Liquid oils can be hydrogenated, using a nickel catalyst in the saturation process and turned into solid such as margarines.
In the production of margarines, sunflower, corn, cotton, sesame, soybean and even fish oil can be used as a starting material.
164
Oxygen And Nitrogen Containing Organic Compounds
Some liquid oils cannot be saturated completely and a semi–solid oil is obtained. The hydrogenation process also gets rid of smelling substances from the fat or oil. Margarines are then made ready for consumption by the addition of coloring, flavoring, salt, milk and butter. Margarines are less preferable than oils for good health. Since the melting points of margarines are higher than that of human body temperature, they may cause some coronary diseases.
8. SAPONIFICATION Hydrolysis of glycerides (fats) in a basic medium produces glycerol (glycerine) and a mixture of salts of long chained carboxylic acids (fatty acids).
Fats, when heated with a solution of NaOH or KOH are hydrolyzed. After the hydrolysis, glycerine and long chained carboxylic acids salts are left, this mixture is soap and the process is called saponification. Soaps are basic salts which are formed by weak fatty acids and strong bases. For this reason, soap solutions show basic properties. Saponification is the reverse process of esterification.
When NaOH is used in the saponification process, a solid soap is produced but when KOH is used, a molten soft soap is produced.
Esters
165
9. CL CLEA EANIN NING G PRO PROCE CESS SS OF OF SOAP SOAPS S Water soluble soluble stains on the surface of clothes can easily be cleaned using water. If our hands get covered in salt, for example, it is enough to wash them with plenty of water. However, However, water isn’t so effective at getting rid of oily stains. Most dirt particles particles (on the surface surface of clothes, on on the skin etc.) become surrounded by a layer of oil or fat. Water molecules molecules alone are unable to get rid of this kind of dirt because they cannot penetrate the oily layer. Soap must be used to disperse this kind of dirt. The chemical structure of soap explains its cleaning ability. There are two main parts of a soap’s structure. Soap molecules contain a nonpolar alkyl tail and a polar head that can interact with the polar water molecules. A soap solution is A drop of water water on a hydropho hydrophobic bic (water (water hating) hatin g) surfac surface. e. Thus, Thus, water is is ineffective ineffective getting getti ng rid of of dirt.
not a true solution, it doesn’t have individual individual fatty acid anions in the water, water, but rather groups of these ions called micelles. Soaps clean oily stains by taking the oil molecules into the nonpolar interior of the micelles which are then carried away by the water. The hydrophobic (water hating) end of a soap molecule can dissolve in an oily stain. Soaps that are used for cleaning are sodium and potassium soaps. The Ca +2 and Mg+2 salts of fatty acids are insoluble in water water,, these salts are known as marble salts.
Soap micelles absorb grease molecules into their interiors so that the grease is suspended in the water and can be washed away.
Soap anions form precipitates with the cations in hard water, i.e, Ca+2 and Mg+2 , and this reduces their cleaning ability, prevent this water may be softened with slaked lime. Magnesium oleate is insoluble in water and soluble in organic solvents, hence it can be used for dry cleaning. Lead stearate is used in the production of salve. Aluminium stearate is used in the manufacture of water-resistant clothes.
(a )
(b)
(c)
a. The tail part of the soap, which is hydrophobic (water hating) hating) dissolves in the oily stain. b. Soap molecules then move between the oil and the surface, surrounding the oil stain. c. The water dissolves the heads of the soap molecules and lifts the oil from the surface. 166
Oxygen And Nitrogen Containing Organic Compounds
10. DETERG DETERGENTS ENTS Detergents are artificial soaps. Their structure is similar to that of soaps; any molecule having nonpolar and polar sections similar to those in soap molecules may disperse oily stains stains on clothes, hence detergents too have a hydrophobic and hydrophilic end. Detergents in which the hydrophilic group is an anion are called anionic detergents. The most common of these are the alkyl benzene sulfanates (ABS) and alkyl sulfates. These are produced by hydrolyzing the bisulfate salts of long chained alcohols with sodium hydroxide. C12H25
C12H25 OH + H 2SO4
dodecyl alcohol
C12H25
Magnesium oleate is insoluble in water.
OSO3H + H 2O
dodecyl bisulfate
OSO3H + NaOH C12H25
dodecyl bisulfite
–
+
OSO3 Na + H2O
sodium dodecyl sulfate
Alkyl sulfate detergents are known as AS detergents, an example of the structure of this type is, –
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2OSO3 Na+ sodium dodecyl sulfate
Most detergents contain the benzene ring in their structure. These kind of detergents are called ABS detergents, as mentioned above. Synthetic detergents are more active cleaners than soaps. They don’t form precipitates with Ca +2 and Mg +2 ions in hard water and are therefore more effective cleaners in hard water than soaps. The cleaning mechanism of synthetic detergents is similar to that of soaps. Na2CO3, Na3PO4 and other basic additives are added to detergents to make their solutions basic so that they are not hydrolyzed in solution. This is necessary as detergents do not have a basic character like soaps.
Detergents are not decomposed into simpler substances by microorganisms, therefore when detergents get into rivers, lakes and ground water water,, they become an environmental environmental problem. Esters
167
1.
What does “derivative of carboxylic acid” mean? Explain
with examples.
2.
What is an ester? Define.
3.
What are are the approxim approximate ate values values of the the angles angles a, b and c?
4.
Name the compounds below.
a. methyl acetate c. phenyl methanoate d. propyl butanoate
Write out the molecul ar formula formulae e for compoun compounds ds below.
b. isobutyl propanoate
e. ethyl butyl ester f.
ethyl propanoate
g. potassium stearate
h. t–butyl ester i.
168
6. 5.
Which of the following c ompounds are est ers?
Oxygen And Nitrogen Containing Organic Compounds
ethyl methanoate
j.
methyl dichloroethanoate
11. Write out the reduction products of the given esters. Which one of the esters has reduction products that are
k. t–butyl benzoate l.
all primary alcohols?
methyl propanoate
m. diethyl ester
n. neopentyl formate o. butyl ester of acetic acid
p. ethyl ester of formic acid r. ethyl ester of –methyl butyric acid
s. o–hydroxyphenylmethyl propanoate
7.
Write the substances formed by the hydrolysis of the given compound.
8.
Both compounds given below are cycloesters. What are the products formed by the hydrolysis of these compounds?
12. Write out the f ollowing reactions of
a. hydrolysis with H2O b. with KOH c. with Na in the presence of alcohol
9.
Which compounds are produced by the reduction and the hydrolysis of the given compound?
13. For
,
write out the following reactions and name the products. s aponification of esters? Give the 10. What is meant by the saponification differences between saponification and hydrolysis?
a. hydrolysis by H2O b. saponification with NaOH Esters
169
14. Write the molecular formulae of the esters produced by the acids and alcohols given below. a. acetic acid–n–propanol
18. What is the molar mass of the ester that is produce d by the reaction between oxalic acid and an excess excess amount of methanol?
b. acetic acid–isobutyl alcohol c. formic acid–benzyl alcohol d. benzoic acid–methanol
19. The molar mass of an ester produced by ethanol and a dicarboxylic acid is 174 g/mol. What is the molecular formula of the carboxylic acid?
e. formic acid–methanol f. butyric acid–propyl alcohol
15. Complete the following reactions and name the products. a. C3H7COOH + CH3COCl b. CH3 – COCl + (CH3)3COH
20. Write down how formed from;
may be
a. a carboxylic acid and an alcohol
c. (COONa)2 + CH3CHBrCH2CH3
b. an acid anhydride and an alcohol c. an acid chloride and an alcohol
21. Explain the following terms. 16. What is the molecular formula of the ester that is produced by the reaction between a carboxylic acid of molar mass mass 60 g/mol g/mol and an alcohol of molar mass mass 60 g/mol?
a. fat
b. glyceride
c. monoglyceride
d. diglyceride
e. triglyceride
f. simple glyceride
g. complex glyceride
h. hydrophobic
i. hydrophilic
22. What are the factors affecting the physical states of fats? 17. I.
Monocarboxylic Acid ———— —— ——— ——— ———— ——— —— 60 g/mol
Monoalcohol ———— ———— ——— ——— 60 g/mol
II.
60 g/mol
46 g/mol
III.
46 g/mol
32 g/mol
Find the molar masses of the esters which are f ormed by the reaction is between the alcohols and acids given above? 170
Oxygen And Nitrogen Containing Organic Compounds
23. How many grams of 70% by mass NaOH solution is needed to neutralize 218.4 grams of a diglyceride of molar mass 624 g/mol? (H2O : 18 g/mol)
24. What is margarine? How is it produced?
30. Match up the types of reactions. a. chlorination of methane b. production of alcohol from methyl ether
25. How many grams of glycerine are needed to produce trioleo glyceride from 16,92 grams of oleic acid?
26. Write the products for the given fat after ;
I. Esterification
ethyl ethyl
II. Hydrolysis
c. production of solid fats from liquid fats
III. Reduction
d. production of wax from palmitic acid and alcohol?
IV. Saponification
e. production of ethanol and ethanoic acid from ethyl ethanoate
V. Substitution reaction
f. production of glycerine and potassium palmitate from glyceryl tripalmitate and KOH
VI. Hydrogenation
a. hydrolysis by water b. reaction with KOH Name the type of reaction.
31. Give the chemical definition of soap and explain what sodium soaps, potassium soaps and ammoniacal soaps are.
32. Why don’t soaps foam in hard water?
27. Write out the reactions of trioleo glyceride (C3H5(C17H33COO)3) with;
33. What is the contribution of the basicity of soaps to their cleaning effect ?
a. NaOH solution at high temperatures b. H2O vapor in an acidic medium
34. What is a detergent? What are their chemical properties?
35. What are the similarities and differe nces between soaps and detergents? 28. What is wax? How is it produced? 36. What are the factors that make deterge nts better cleaning agents than soaps?
29. What are the differences between wax, fat, butter and mineral oil (hydraulic oil)?
37. What do AS, ABS and LAB stand for? What are the effec t of these subst ances on the environment? Esters
171
1.
Esters are;
5.
I. Alkyl salts of carboxylic acids
II. Formed by the attachment of an alkoxy group to an III. Oxidation products of carboxylic acids
D) II and III
What is the correct name f or the compound above ?
Which of the above statements , is(are) correct? B) I and II
acyl group
A) I only
A) Isopentyl ester of –chloroacetic acid
C) III only
B) Pentyl ester of –chloroacetic acid
E) I, II and III
C)
–chloro ethyl ester of isovaleric acid
D) Isopentyl ester of –chloropropionic acid E) 2–chloropropionic acid
2.
Which one of the following groups cannot be attached to the carbon of the functional group of an ester of molar mass 102 g/mol? A) H–
B) CH 3–
C) C2H5–
D) C3H7–
E) C4H9–
6.
Compounds formed by the reaction of inorganic or organic acids with alcohols are called esters. According to this, which one of the given compounds is not an ester?
3.
Which one of the following compounds does not contain an acyl group? A) Ketones
B) Esters
D) Amides
C) Carboxylic acids
E) Ethers
I. Formic acid
4.
II. Acetic acid III. Propionic acid Which of the above acids does not have an ester isomer? A) I only
B) II only D) II and III
172
C) I and II E) I, II and III
Oxygen And Nitrogen Containing Organic Compounds
7.
What is the name of CH 3COOCH3 ? A) Methyl methanoate
B) Ethyl methanoate
C) Ethyl acetate
D) Methyl acetate E) Methyl formate
8.
Which one of the compounds shown below is isopropyl–p–methyl benzoate?
11.
Which Whic h of the comp compound oundss show n abov above e can be
hydrolyzed with an acid catalyst?
A) I only
B) I and II D) II IIII on only ly
C) I and III E) IV on E) only ly
12. What is the type of reaction occurring when isobutyl acetate reacts with NaOH? 9.
Which of the given pairs of compounds are isomers of each other?
A) Oxid Oxidatio ation n
B) Addit ion
D) Esteri Esterificati fication on
I. Methyl acetate acetate – methyl methyl propanoa propanoate te
C) Polymer Polymerizat ization ion E) Sapon Saponificat ification ion
II. Phenyl Phenylacetic acetic acid acid – methyl methyl propanoate propanoate III. Benzoi Benzoic c acid – phenyl phenyl formate formate A) I only
B) III only D) II and III
C) I and II
13. Which of the following pair of compounds are formed by the reaction of methyl oleate with NaOH?
E) I, II and III A) Methyl alcohol and sodiumoleate B) Meth Methyl yl alc alcohol ohol and olei oleic c acid acid C) Oleic alcoho alcoholl and and methanoi methanoic c acid acid D) Oleic acid and methano methanoic ic acid acid
10. For esters; I. Hydrog Hydrogen en bonds exist exist between their their molecules. molecules.
E) Oleic alcoho alcoholl and and sodium sodium methy methylate late
II. They are more more soluble soluble in water than than in alcohols. alcohols. III. Liquid Liquidss esters are are good organic organic solvents. solvents. Which of the above statements is(are) correct? A) I only
B) III only D) I and III
C) I and II E ) I, II and III
14. Which one of the following species is able to break up the structure of the acyl group in an ester? A) H2O
B) KOH B)
C) H2
D) NH3
E) Na NaOH OH
Esters
173
S t f
h
w
b t
h
o c
b
The reaction between carboxylic acids and alcohols produces these compounds (E) (6) The common name of this compound is methyl ester (M) (16) These compounds are triesters of fatty acids and glycerine (F) (4) The ester derived from formic acid that that has one H atom bonded to C the atom of the functional group (M) (13) When esters are heated with aqueous solutions of strong bases such as NaOH and KOH, the salt of the carboxylic acid is produced which which is known as a ____________ (S) (4) Fats may be solid, liquid or molten depending upon the amount of ____________ they contain. (G) (9) If an oil is ____________ , this is because because of the double bonds in the fatty acids of this oil. (U) (11) (11) Because their melting points are higher than human body temperature , they cause coronary diseases. These are not preferred oils for human health. (M) (10) Water containing Ca2+ and Mg2+ ions Water ____________ (H) (9)
is known
as
This is used to describe molecules or molecular groups that mix poorly with water. (H) (11)
174
Oxygen And Nitrogen Containing Organic Compounds
INTRODUCTION Carbohydrates are the most common compounds we encounter in daily life. The doors we use in our houses, furniture in the form of wood, most of our food, clothes made from cotton and linen are carbohydrates. Carbohydrates are the most abundant organic compounds in nature, although they are scarce in living organisms. Carbohydrates are the main energy and nutrition source for all living organisms including human beings. Some of the more common carbohydrates carbohydrates in our daily life are; cellulose which exists in plant tissue and is a raw material for paper, paper, starch which is an energy resource for plants, glycogen which is used as an energy resource in animals and humans, glucose and fructose which exist in fruit and honey, lactose, maltose and sucrose. Carbohydrates are mostly produced by green plants. In the leaf of a green plant carbon dioxide from the air and water, taken in from the roots of the plant, are converted into glucose by the catalysts chlorophyll and sunlight. This process is known as photosynthesis. Plants, in fact, can be viewed as a natural laboratory laboratory that synthesizes organic nutrition materials. Formaldehyde is produced in photosynthesis as a primary Photosynthesis occurs in the leaves of green plants. Plants take in CO 2 in sunlight (during the daytime) and give out O2 ; humans and animals use O 2 and produce CO2. The oxygen abundance in the air is 21% by volume which is the most suitable suitable percentage percentage for the survival of living organisms. The CO 2 and O2 balance is kept constant constant by the production of CO 2 by animals and humans humans and of O2 by plants. IfIf the abundance abundance of oxy gen in the air were 50%, everything flammable would burn up instanta neously and it were 10 %, it would be very difficult can be for humans and ani mals to survive. Thus, life life would would not not exist as we know it.
product. However, as formaldehyde is a poisonous compound, plants polymerize it into starch, cellulose and other complex complex compounds thereby transforming transforming it into useful, non-toxic substances. The general equation of photosynthesis is sunlight
C6H12O6(s)+ 6O2(g) 6CO2(g) + 6H2O(l) chlorophyll
As can be seen from the reaction, plants take carbon dioxide from the air and convert it into oxygen. Living organisms can then use this oxygen to break down carbohydrates to produce energy in the process of respiration. C6H12O6(s) + 6O 2(g) 6CO2(g) + 6H 2O(l) + Energy The carbon dioxide produced can then used again by plants to produce more carbohydrates. Photosynthesis and respiration respiration in living organisms organisms are the reverse of each other other and so the balance between the carbon dioxide and oxygen oxygen in the atmosphere is controlled by these two processes.
1. STR STRUCT UCTURE URE OF CA CARBO RBOHYD HYDRA RATES TES The empirical formula of the most of carbohydrates is CH 2O and the general formula is Cn(H2O)m. Here, n=m or n m. For this reason, carbohydrates may be thought of as hydrated carbons (hence the name), though they do not contain actual water molecules. The ratio of hydrogen atoms to oxygen atoms in a carbohydrate molecule is 2:1, as it is in water. water. 176
Oxygen And Nitrogen Containing Organic Compounds
The simplest compound with the general formula formula of a carbohydrate is formaldeformalde-
The general formula of carbohydrates is
hyde which has the formula CH2O. Hence, carbohydrates may be considered as
C n(H 2O)m. But, a compound that has a
polymers of formaldehyde.
formula of C n(H 2O)m is not necessarily a carbohydrate. For example, acetic acid
has the formula C 2(H 2O) 2 but is not a
carbohydrate.
Carbohydrates contain the functional groups;
alcohol (–OH), aldehyde (
) an and/or ke ketone (
).
Hence carbohydrates may be defined as polyalcohols p olyalcohols of aldehydes and ketones. In large carbohydrate molecules, ketone and aldehyde groups are not directly seen, but when they are hydrolyzed, the aldehyde or ketone groups become apparent.
2. NOM NOMENC ENCLA LATUR TURE E OF CARBOH CARBOHYDRA YDRATES TES If a carbohydrate contains of an aldehyde group, it is named as an aldose; if it contains a keto group, it is called a ketose. The number of carbon atoms determines the name of the carbohydrate.
Aldoses
Ketoses
Carbohydrates
177
C* indicates an asymmetric carbon atom, if the number of asymmetric carbon atoms equals n, the optical isomers of the compound is calculated as 2 n.
1 Name the following carbohydrates.
a. aldopentose
b. ketopentose
d. ketohex ose
e. ketotetrose
c. aldohex ose
3. CLASSIFICATION OF CARBOHYDRATES Carbohydrates can be classified as monosaccharides, disaccharides and polysaccharides according to the number of their carbon atoms.
3.1. MONOSACCHARIDES General Properties Monos accharides, commo nly found in foods, are hexoses. Most monosaccharides can be fermented.
Fermentation of Glucose
yeast
C 6 H 12O6 2C 2 H 5OH + 2CO 2
smaller carbohydrate molecules. duction of energy in the metabolic processes of living organisms. It is stored in the liver and muscles. It is present in grapes and honey.
2. Monosaccharides are white, crystalline, sweet compounds. They are very sol-
2. Formation of lactic acid.
uble in water due to hydrogen bonding. They are only slightly s oluble in alco-
yeast
2CH 3 ––CH––COOH l OH
3. Fatty acid. C 6 H 12O6 C 3 H 7 COOH + 2CO 2 + 2H 2 178
between two and nine. Monosaccharides cannot be hydrolyzed to obtain Glucose is a well-known monosaccharide. It is vitally important for the pro-
1. Preparation of ethyl alcohol.
C 6 H 12O6
1. The number of carbon atoms in the structure of a monosaccharide is
hol and insoluble in nonpolar solvents such as ether and hydrocarbons.
3. The most important monosaccharides are glucose, fructose, mannose and galactose. Their molecular formulae are identical (C 6H12O6) and as such they are all structural isomers of each other.
Oxygen And Nitrogen Containing Organic Compounds
4. Because of their structural formulae, monosaccharides have four asymmet-
Glucose, one of the most important member of monosaccharides, is found in grapes.
rical carbon atoms in their solid state. Consequently, they show optical activity. For example, glucose, which is known as an aldohexose, contains four asymmetrical carbon atoms, so it has n
2 = 24 = 16 optical isomers.
Fructose, known as fruit sugar as fruits contain large amounts of it , is sweeter than saccharose. It is found mostly in honey (1/3 of honey is fructose).
Cyclic Structures of Monosaccharides Monosaccharides can have both cyclic and straight chain structure s. Cyclomonosaccharides are formed when straight-chain monosaccharides are dissolved in water. In this case, the number of asymmetrical carbon atoms increases to five. This process is known as hemiacetal formation . Let us examine the formation of the cyclic structure in the glucose molecule.
Honey is an important source of mono saccharides. Carbohydrates
179
a. The dissolving of D–glucose in water to form a cyclic structure. b. –D–glucose; –OH groups on 1 st and 4th carbons are in the cis position. c. –D–glucose; –OH groups on 1 st and 4th carbons are in the trans position.
2 Show the cyclic form of fructose when it is dissolved in water.
As we know, fructose is a ketohexose (the carbonyl group is on the second carbon). When it is dissolved in water an oxygen bridge is formed between its 2 nd and 5th carbon atoms.
Oxidation of Monosaccharides To determine the structure of carbohydrates the following oxidizing agents are used.
1. Oxidation by Tollens’ and Fehling’s Reagents a. Aldoses reduce Tollens’ reagent because of the aldehyde group in their structure. They also reduce Fehling’s solution in the presence of copper ions in basic solution. The deep blue color of the solution is turned the red due to cuprous oxide precipitation. 180
Oxygen And Nitrogen Containing Organic Compounds
This reducing property is used to measure blood sugar in terms of glucose units. If a sample of urea is mixed with Fehling’s reagent, a red precipitate is observed.
b. Ketoses also reduce both Fehling’s and Tollens’ reagents. For example, fructose, a ketohexose, does not show reducing properties in the solid state, but in solution it reacts with Tollens’ and Fehling’s reagents as follows.
All monosaccharides and disaccharides (except saccharose) are reducing sugars. However, polysaccharides are not reducing sugars.
Carbohydrates
181
2. Oxidation of Monosaccharides with Bromine Water Bromine water is an oxidizing agent that oxidizes the aldehyde group to the carboxyl group and aldoses to aldonic acids.
3. Oxidation of Monosaccharides with Nitric Acid Nitric acid, a stronger oxidizing agent than bromine water, oxidizes both the aldehyde and the –CH2OH group to the carboxyl group and aldaric acid is formed.
3 36 grams of an aldose with the general formula of C nH2nOn is reacted with Tollens’ reagent and 43.2 grams of silver is precipitated. What is the molecular formula of the aldose? (C : 12 g/mol, H : 1 g/mol, O : 16 g/mol, Ag : 108 g/mol)
Aldose with Tollens’ reagent; CnH2nOn + 2Ag(NH3)2+ + 2OH– CnH2nOn+1 + 2Ag + 4NH3 + H2O Molar mass of aldose C nH2nOn = 12n + 2n . 1 + 16n = 30n g/mol 30n grams of aldose precipitates
216 g Ag
36 grams of aldose precipitates 43.2 g Ag ———————————————————————————— 36 . 216 n = —————— = 6 30 . 43.2 Molecular formula is C 6H12O6. 182
Oxygen And Nitrogen Containing Organic Compounds
Detection of Sugar in Urine Most sugars contain aldehyde or ketone groups in their structure. Hence, sugars can reduce metallic ions such as Cu 2+, Hg2+, Bi3+ and Ag1+ as they are oxidized to carboxylic acids. This property can be used to detect the amount of sugar in blood from urine samples .Although there are many different methods to detect sugar in urine, the most important one is using Fehling’s solution (reagent). The procedure of this experiment is as follows: 1. In a test tube, add some Fehling I solution (7% CuSO 4 solution). 2. Next, add an equal volume of Fehling II solution (a solution of sodium
potassium tartrate and NaOH) and make up to 100 ml with water. 3. Mix the solution well to produce a dark blue color. 4. Next, boil the solution (Attention: the dark blue color should not disappear,
if the color disappears, the indicator or test tube is not clean). 5. Finally the urine is added to the solution. (The amount of urine should not
exceed the amount of the indicator). If the urine contains glucose (sugar) a yel low or red precipitate forms in the test tube.
The amount of glucose in blood should be around 80-120 mg. Glucose disorder in blood is related to the production of the hormone insulin.
4 500 g of a sample is taken from a glucose solution 1.2% by mass. If this sample is reacted with excess Fehling’s solution, how many grams of Cu 2O will be precipitated? (C6H12O6 : 180 g/mol, Cu2O : 143 g/mol) Carbohydrates
183
Let us find the total amount of glucose 1.2 mglucose = 500 . ——— = 6 g. 100 The reaction of glucose with Fehling’s solution:
According to the reaction; 180 grams of glucose
precipitates 143 grams of Cu2O
6 grams of glucose precipitates x grams of Cu 2O ———————————————————————————————— 6 . 143 x = ————— = 4.77 180 x = 4.77 grams of Cu 2O precipitates
Reduction of Monosaccharides Aldehyde and ketone groups in monosaccharides can be reduced by strong reducing agents. For example D–glucose can be reduced to D–glucitol (sorbitol) by NaBH4 or H2 in the presence of Pt.
184
Oxygen And Nitrogen Containing Organic Compounds
5 Write the reactions of D-ribose (an aldopentose) with;
a. Tollens’ reagent
b. NaBH4
6 Write the reactions of D-ribulose (a ketopentose) with;
a. Tollens’ reagent
b. NaBH4
Carbohydrates
185
3.2. DISACCHARIDES Condensation compounds derived by the elimination of a water molecule from two monosaccharide molecules are called disaccharides. The two monosaccharides are linked via an oxygen bridge. The aldol condensation is the reaction of two identical aldehydes or ketones in the presence of a base such as sodium carbonate, barium hydroxide or dilute sodium hydroxide.
General Properties 1. Their general formula is C 12H22O11 . 2. They are white, crystalline and sweet compounds. 3. All of them rotate plane–polarized light to the right. 4. They hydrolyse to form monosaccharides. 5. In nature, the most important disaccharides are sucrose (table sugar, cane sugar or beet sugar) maltose (barley sugar), lactose (milk sugar) and cellobiose.
Saccharose (Sucrose) Saccharose is formed by linking of one molecule of glucose to a fructose molecule. It occurs widely in plants and is particularly abundant in sugar cane and sugar beet from which it is extracted and refined for use as table sugar. It dissolves well in water and is slightly soluble in alcohol. When sucrose is digested, If sucrose is heated above its melting point it turns into caramel which is used in the production of candies.
glucose and fructose are formed which are then absorbed into the blood. –H2O
C6H12O6 + C6H12O6 glucose
C12H22O11 + H2O
fructose
sucrose (table sugar)
Or in more detail,
186
Oxygen And Nitrogen Containing Organic Compounds
Cyclic structure of sucrose.
Saccharose (sucrose) does not show reducing properties as it does not contain a carbonyl group (aldehyde, -hydroxy ketone or hemiacetal group). Hence it does not react with Tollens’ and Fehling’s reagents.
Lactose Lactose is known as milk sugar and occurs in the milk of all mammals. Human milk contains 6%, and cow’s milk 4% lactose. C6H12O6 + C6H12O6 glucose
C12H22O11 + H2O
galactose
lactose
The structure of lactose is given below.
Upon reaction with dilute acids, it is hydrolyzed to glucose and galactose.
Maltose Maltose is a disaccharide that is present free in small quantities in barley grains
Lactose is the substance which gives a sweet taste to human and animal milk. Glucose and galactose may be converted into lactic and butyric acids by the effect of some yeasts, this causes milk to turn sour.
and other plants. However, it is more commonly produced by the action of the amylase enzyme on starch or glycogen. Its melting point is 102-103 °C. It is used in the production of soft drinks and foods. Maltose, because of the free aldehyde group in its structure, reduces Fehling’s solution and produces a monocarboxylic acid (maltonic acid) with bromine water. When hydrolyzed by dilute acids maltose forms two glucose molecules.
Carbohydrates
187
It is the only dissaccharide that rotates plane–polarized light to the left. H2O
C12H22O11
C6H12O6 + C6H12O6
maltose
glucose
glucose
maltose
Cellobiose Cellobiose is produced by the partial hydrolysis of cellulose (a polysaccharide) . If the hydrolysis continues, two molecules of glucose are produced. Cellobiose is very similar to maltose, they are geometrical isomers. In some countries, cellobiose is produced by heating wood with hot acids and used as fodder for animals. +H2O
C12H22O11 + cellobiose
H
C6H12O6 + C6H12O6 glucose
glucose
3.3. POLYSACCHARIDES Polysaccharides are polymers of monosaccharides. Polysaccharides are formed by linking many monosaccharides together with an oxygen bridge.
General Properties 1. Their general formula is (C 6H10O5)n . 2. They occur in the roots, tubers and seeds of plants. 3. They are noncrystalline, amorphous and tasteless substances; these are the most significant properties differentiating polysaccharides from monosaccharides. 4. They are the only carbohydrates that are insoluble in water, they form a colloidal structure when mixed with water. They are also insoluble in alcohols. 5. They can be broken down into monosaccharides when hydrolyzed. 6. The most important polysaccharides in nature are; a. Starch, b. Glycogen, c. Dextrin, d. Cellulose.
188
Oxygen And Nitrogen Containing Organic Compounds
Starch Starch is the most important polysaccharide and is formed by combining glucose molecules with a glycosidic linkage. Corn, potatoes, rice and the roots of plants and seeds are the main sources of starch. Starch is an essential nutritional resource. One molecule of starch consists of thousands of glucose molecules.
Starch is an essential food for humans. Bread is composed of 50–75% starch.
Representation of the starch molecule.
Starch is insoluble in water. When it is heated with water, it is broken down into simpler carbohydrates and forms a colloidal mixture. Starch does not reduce Fehling’s reagent, though undergoes a characteristic reaction with iodine, forming a deep blue solution. Since it contains many –OH groups in its structure, starch absorbs moisture well. When starch is heated with a dilute acid, it undergoes a hydrolysis reaction resulting in glucose as the final product. H2O
+ H2 O
H 2O
(C6H10O5)n (C6H10O5)n C12H22O11 2C6H12O6 starch
H+
dextrin
H+
maltose
H+
glucose
Glycogen Glycogen, stored in the livers and cells of animals, is the main carbohydrate resource for animals. The molecule is built up of a large number of monosac-
Potato is one of the main source of starch.
charide units by glucoside links. It is insoluble in water and gives a pink color upon reaction with iodine. It is broken down in the digestive system to give glucose and maltose.
Dextrin Dextrins are produced by heating up starch to 160 – 228°C. Hence dextrins are found in the crusts of bread. They dissolve in water but form a precipitate in alcohols. They can also be obtained from the hydrolysis of starch with dilute acid at low temperature. Dextrins are mixtures of polysaccharides having 5–15 glucose un its in their structure. They are sticky, sweet substances used in the manufacture of adhesives and soft drinks. Carbohydrates
189
Cellulose Cellulose is the most abundant organic substance in nature. The walls of plant cells are made of cellulose. The main cellulose sources in nature are wood, grass, hay, cotton, linen and hemp. Cellulose molecules may be formed from more than 3500 glucose units. Cellulose is an amorphous substance, insoluble in water and unlike other polysaccharides, resistant to dilute acids and bases. However, it can be hydrolyzed by dilute acids under high pressures and temperatures. +H2O
+
Cellulose
H
+H2O
+
Cellobiose
H
Glucose
Structure of cellulose
Cellulose is an important raw material for many different commercial substances:
1. Trinitrocellulose ([C6H7O2(ONO2)3]n) is known as cotton gunpowder and is used to produce smokeless explosives . It is also used in the production of films and artificial leather. H2SO4
[C6H7O2(OH)3]n + 3nHNO3
[C6H7O2(ONO2)3]n + 3nH2O cellulose trinitrate (cotton gunpowder)
2. Rayon is produced by dissolving cellulose in carbon disulfide in a basic medium. This reaction yields cellulose xanthate. The solution of cellulose xanthate Cellulose is the main component of wood and its derivatives. 60-70% of wood is cellulose.
is then passed through a small slit into an acidic solution. This reaction leads to precipitation in the form of a fiber. It is this fiber that is rayon.
3. After treating ce llulose with sulfuric acid and acetic acid, cellulose triacetate is produced. Cellulose triacetate and its derivatives are used in the textile industry and in the production of films.
4. Cellulose fibers are the most important material in paper production.
190
Oxygen And Nitrogen Containing Organic Compounds
1.
Which materials in your house contain carbohydrates? Research.
2.
What is the importance of carbohydrates for living organisms?
3.
12. Classify carbohydrates and give one example from each group.
13. What are the general properties of monosaccharides?
What are the most important carbohydrates around us?
4.
Explain photosynthesis.
5.
What is chloro phyll? What is its function?
14. What is the importance of glucose among the monosaccharides?
15. What is the reason for the easy hydrolysis of glucose in water? 6.
What is the primary product of the photosynthesis process?
7.
Explain the relationship between respiration and photosynthesis. Why is the balance between these two processes important for living organisms?
8.
Define carbohydrates and give their general formulae.
9.
Describe the structures of carbohydrates.
16. What is mutarotation? Explain
17. Explain how hemiacetals are formed.
18. What are the main oxidizing agents used to oxidize monosaccharides to carbonic acids?
10. Which functional groups do carbohydrates contain? Explain.
11. Write the structural formulae of the carbohydrates given below.
19. What do you understand from the terms -hydroxy and -hydroxy?
a. Ketopentose b. Aldotetrose c. Ketohexose d. Aldohexose
20. What are the functional groups that exist in monosaccharides? Carbohydrates
191
21. Why don’t ketose s of monosaccharides show reducing properties when they are split? Explain.
22. What is the molecular formula of the aldose of which 36 grams reacts with Fehling’s solution to produce 28,6
29. What is the most important property that differentiates monosaccharides from disaccharides?
30. Which monosaccharides are prod uced by the hydrolysis of sucrose (saccharose)?
grams of Cu2O?
23. How many grams of Cu2O are formed when 30 grams
31. What are the reasons for saccharose showing reducing properties?
of 60% glucose s olution react with excess Fehling’s solution? (Cu: 63.5 g/mol)
32. What is invert sugar? Explain. 24. How many grams of silver are produced when 45 grams of 80% glucose solution react with ammoniacal silver nitrate solution (T (Tollens’ ollens’ reagent)?
33. What are the general properties of polysaccharides?
25. When 20 grams of glucose solution react with ammoniacal copper(I) chloride solution (Fehling’s reagent) 14.3 grams of Cu2O are precipitated. What is the mass per-
34. What is the most important property of polysaccharides that differentiates them from other carbohydrates?
centage of this solution?
35. What are the most important polysaccharides in nature? 26. 45 grams of an aldose having the general formula CnH2nOn produces 35.75 grams of Cu2O when reacted with excess Fehling’s solution. According to this; (C : 12 12 g/mol g/mol,, H : 1 g/mol, g/mol, O : 16 g/mol g/mol))
a. What is its molecular formula?
36. What is the importance of starch for living organisms? Which plants co ntain starch?
b. What is its molar mass?
27. What are the general properties of disaccharides?
28. What are the most important disaccharides in nature? 192
Oxygen And Nitrogen Containing Organic Compounds
37. What are the main sources of dextrin, glycogen and ce llulose?
38. In which areas is cellulose used?
1.
Which one of the following is the main source of carbo-
5.
hydrates? A) Stones
B) Sedimentary rock
C) Green plants
D) Soil
E) Air
Which of the following is(are) correct for the compounds above? They are; I. opt optica ically lly activ active e
2.
Which one of the following is incorrect for photosynthesis?
II. isom isomers ers of each each other other III.. car III carbohy bohydra drates tes
A) It occurs in the porous leaves of green plants.
A) I only
B) Sunli Sunlight ght is is used as an energy source.
B) II only D) II and III
C) It tu turn rnss CO2 from the air into carbohydrates.
C) III only E) I and II E)
D) Respiration Respiration in animal animalss and humans humans is the same as photosynthesis. E) It occurs occurs using using the the catalyst catalyst chlorop chlorophyll. hyll.
3.
Fill in the blank given below with suitable word. Carbohydrates are ............... that contain aldehyde or ketone groups in their structures. A) Ethe Ethers rs
B) Este Esters rs
D) Pol Polyester yesterss
4.
C) Alde Aldehyde hydess E) Pol Polyalco yalcohols hols
6.
Which one one of the following following is incorrect for carbohydrates?
A) Monosaccharides are the simplest sugars . B) Monosac Monosaccharid charides es are straight straight chained chained molecule molecules. s. C) Disaccharides Disaccharides are are formed by the combina combination tion of two two monosaccharide molecules.
Which of the molecules above is (are) c arbohydrates?
D) If three or or more monosac monosaccharid charide e molecules molecules comcombine they form polysaccharides.
A) I only
E) Monosaccharid Monosaccharides es cannot cannot be hydrolyz hydrolyzed ed to simpler simpler molecules.
B) II only D) II and III
C) III only E) I and II E)
Carbohydrates
193
7.
Which one of the following is incorrect for monosaccharides?
10. The fermentation reaction of glucose is; C6H12O6
A) They cannot be hydrolyzed to simpler molecules.
yeast
2C2H5OH + 2CO2
B) They can can enter the the blood stream stream directly directly..
How many grams of ethyl alcohol is produced from 90 grams of a 60% of glucose solution?
C) Monosac Monosaccharid charides es are the only only class class of carbohydrat carbohydrates es
A) 13.8
B) 18.4
C) 23
D) 27.6
E) 32.2
that can be fermented. D) The most import important ant are glucose, glucose, fructose fructose,, mannose mannose and galactose. E) They do not show optical optical activ activity ity..
11. Which statement is incorrect for disaccharides? A) Their general fo rmula is C12H22O11 . B) They are all all soluble soluble in water water..
8.
Which one of the f ollowing is wrong for glucose? A) It is the most common sugar in nature and is known
C) They are are the condensati condensation on product product of at least least two monosaccharides. D) The most import important ant are sacchar saccharose, ose, malto maltose, se, laclactose and cellobiose.
as blood sugar. B) It can can be fermen fermented ted by yeast yeast.. C) It can be oxidized oxidized to a carboxy carboxylic lic acid by Fehling Fehling’s ’s
E) They are are more soluble soluble in alcohol alcohol than in water water..
reagent. D) It can be reduced to to a polyalcoho polyalcoholl by NaBH4 . E) Mutaro Mutarotation tation is not a proper property ty of aqueous aqueous solution solutionss of glucose.
12. Which statement is correct for sucrose? A) It is wide ly found in grapes and honey.
9.
How many grams of 20% glucose solution should be used to produce 28.6 g of Cu2O from Fehling’s solution? (C6H12O6 : 180 g/mol, Cu2O : 143 g/mo g/mol) l) A) 180
194
B) 360
C) 90
D) 45
B) It is formed formed by combinati combination on of two molecule moleculess of glucose. C) It is slightly slightly soluble soluble in water water and highly highly soluble soluble in alcohol. D) It doesn’t doesn’t show any optical optical activit activityy.
E) 286
Oxygen And Nitrogen Containing Organic Compounds
E) It doesn’t doesn’t react with Fehling Fehling’s ’s and Tollens Tollens’’ reagents.
13. Which one of the f ollowing statements is incorrect? A) Lactose is known as milk sugar and is not found in plants. B) Maltose Maltose is formed formed by the combina combination tion of two two molecules of glucose. C) Lactose is formed by by linking linking glucose glucose and mannose mannose molecules together by glucoside bonds. D) Maltose and cellobiose cellobiose are are geometrical geometrical isomers isomers of each other.
15. Which o ne of the follow ing is incorrect for polysaccharides? A) They are highly soluble in water. B) They don’t don’t have a stable stable crystallin crystalline e structure. structure. C) When they they are hydrolyz hydrolyzed, ed, they can be broken broken down down into monosaccharides. D) They are are found in in plant and and animal animal tissues. tissues. E) The most most common common polysacchar polysaccharides ides are starch starch,, cellulose and glycogen.
E) Cellobi Cellobiose ose shows shows exhib exhibits its propert properties. ies.
14. What is the mass percentage of a saccharose solution if 228 grams of it produces 72 grams of glucose after hydrolysis in acidic medium? (C : 12 12 g/mol g/mol,, H : 1 g/mol, g/mol, O : 16 g/mol g/mol)) A) 60
B) 50
C) 40
D) 30
E) 20
o f the following statements describing poly16. Which one of saccharides is incorrect? A) They don’t have a definite melting point, they sublime. B) Starch reacts with with Fehling Fehling’s ’s reagent. reagent. C) The hydrolysis hydrolysis of starch starch by dilute dilute acid acid produces produces dextrin. D) Cellulose Cellulose is the most common common organic organic substance substance and forms the walls of plant cells. E) The Their ir gener general al formu formula la is (C (C6H10O5)n .
Carbohydrates
195
– C t
c
a
p
y
a
P i t
c
p
i t
g
C
A It is the process process by which carbon carbon dioxide from air and water from the roots of plants are converted into glucose under the catalysts of chlorophyll and sunlight. Glucose molecules can be combined to form large molecules of __________, which serves as as a reserve reserve material. It is an essential source of nutrition. Corn, potatoes, rice and seeds are the main sources of this substance. It is the most important monosaccharide, it is the most abundant sugar found in nature and in animals. It is known as fruit sugar because large amounts of this sugar exist in fruits. A hydroxy aldehyde, a hydroxy ketone or a substance derived from these compounds. A carbohydrate molecule that is composed of two monosaccharide monosacchar ide units
196
Oxygen And Nitrogen Containing Organic Compounds
D A class cl ass of carbohydrate that contains many monosaccharide units, examples are starch and cellulose. The chief constituent of the cell wall of all plants and the most abundant organic substance found in nature. It is the main component of wood. If a carbohydrate contains a keto group it is named as a ______________ If a carbohydrate contains an aldehyde group it is named as an _______________
INTRODUCTION Amines, amides, amino acids and proteins, can be straight chained or branched molecules. Amines are derivatives of ammonia having general formula R Amides have the general formula R
CO
NH2 .
Amino acids are compounds having both an amine ( group (
NH 2 .
NH2) and a carboxyl
COOH) in their structure.
Proteins are long chained amino acid molecules.
1. AMINES Amines are weak bases that can be described as organic derivatives of ammonia or as alkylated ammonia compounds. The functional group of amines is the amino group (
NH2). The nitrogen atom
undergoes sp3 hybridization and is attached to one or more carbon atoms. Amines can be classified as primary, secondary or tertiary amines depending upon the number of alkyl groups attached to the nitrogen atom.
Heterocyclic Amines In these compounds N is a part of a ring structure.
R can be an alkyl or an aryl group.
1.1. NOMENCLATURE OF AMINES Common Names 1. Primary amines are commonly called alkylamines, though systematically, they are named alkaneamines.
198
Oxygen And Nitrogen Containing Organic Compounds
Some Amines
2. When naming the secondary and tertiary amines, t he smaller group is written first and the other groups are added before the word “–amine”. If the groups are the same , the di- or tri- prefixes are used . In common nomenclature we use the locant N to designate substituents attached to a nitrogen
Cocaine and morphine are two very
atom.
Amines occur widely in plants and animals. They can easily be extracted from their sources by treatment with acids. Amines are basic compounds, alternatively named as ALKALOIDS. Today, there are 5000 alkaloid compounds known to be biologically active.
well known alkaloids. Cocaine is a compound extracted from the leaves of the coca plant. Long term usage of cocaine causes addiction and harms the central nervous system.
Morphine, also known as ascocaine, is
also an addictive substance. The diacetate salt of morphine, heroin, is as addictive as morphine and cocaine.
Many different alkaloids, such as nicotine and quinine, contain more than one nitrogen atom in their structure. Quinine is used in medicine to cure the
3. In the systematic naming (IUPAC) of these compounds, the –NH 2 amine group is called the amino group. This naming is generally used in the case of alcohols and acids.
disease malaria. Nicotine is a colorless, poisonous alkaloid present in large amounts in tobacco. As it is highly toxic, its salts are used as i nsecticides.
Amines, Amides And Amino Acids
199
1
Have you ever heard? Chocolate contains phenylethylamine, a chemical related to psychomotor stimulants and raises blood pressure and blood glucose levels. The result is that we feel more alert and gives us a sense of well being.
Name the following amine compounds.
Phenylethylamine is known as the “love drug” and is thought to be the reason why chocolate is said to be an aphrodisiac. It is a chemical that mimics the brain chemistry of a person in love, so when levels of phenylethylamine are high in the body it relieves depression from unrequited love. This is one of the reasons so many women love chocolate - it really changes mood of person.
a. dimethylethylamine
b. triethylamine
c. tert-butylamine
d. cyclopentylamine
e. phenylamine (aniline)
f. 2 – phenylethylamine
2 Write the structures for the given compounds.
a. Diethylmethylamine b. 2-aminopentane c. 1,4-diamino - 1,4 - butanediol d. Ethylmethylisopropylamine
3 What is the molecular formula of the tertiary amine which contains 65.75% C, 19.18%N and 15.07%H, by mass? (C : 12 g/mol, N : 14 g/mol, H : 1 g/mol) 200
Oxygen And Nitrogen Containing Organic Compounds
Let us assume we have 100 g of this amine. Then the mole ratio of the elements are 65.75 g nC = ––––––––––– = 5.48 mol, 12 g/mol
19.18 g n N = ––––––––––– = 1.37 mol 14 g/mol
15.07 nH = ––––––––– = 15.07 mol 1 g/mol If the mole numbers of the compounds are divided by smallest mole number, 1.37 mol, the following integers are found. 5.48 nC = ––––––– = 4 mol 1.37
1.37 nN = –––––– = 1 mol 1.37
15.07 nH = ––––––– = 11 mol 1.37
C4H11N is the formula. Since this is a tertiary amine the structural formula must be;
1.2. PHYSICAL PROPERTIES Small amine molecules are generally gaseous and are soluble in water. Amines have a very bad odor, similar to that of ammonia and tainted fish. Amines, like ammonia, are polar compounds (though tertiary amines less so as they have no N–H bond). Because of the N–H bonds in their structures, primary and secondary amines form hydrogen bonds between their molecules. The boiling points of amines are higher than those of the equivalent alkanes and Amines have a tainted fish smell.
ethers but lower than the equivalent alcohols and carboxylic acids. C2H5
O
C2H5
diethyl ether bp : 54.6 °C
(C2H5)2NH
CH3CH2CH2CH2OH
diethyl amine bp : 55 °C
1 – butanol bp : 118 °C
Since tertiary amines do not contain N–H bonds, they can not form
hydrogen bonds in the liquid state and so t heir boiling points are lower than those of primary and secondary amines.
All low molecular weight amines are very soluble in water.
Because of the lone pair of electrons on the nitro gen atoms, all amines form hydrogen bonds with water. Amines, Amides And Amino Acids
201
Name
Structure
Melting Point (°C)
Boiling Point (°C)
Solubility (g/100 mL water)
Kb
Methylamine
CH3NH2
– 94
–6
very soluble
4.4 · 10 –4
Ethylamine
CH3CH2NH2
–
81
17
very soluble
4.7 · 10 –4
Propylamine
CH3CH2CH2NH2
–
83
49
very soluble
4.0 · 10 –4
Dimethylamine
(CH3)2NH
–
92
7
slightly soluble
5.0 · 10 –4
Trimethylamine
(CH3)3N
– 117
3
slightly soluble
6.0 · 10 –5
Aniline
C6H5NH2
–
184
soluble
4.2 · 10 –10
6
Table 1: Physical properties of some amines.
1.3. CHEMICAL PROPERTIES AND REACTIONS Amines are basic compounds. They form hydrogen bonds upon dissolving in water because the nitrogen atom in the amine has a lone pair of electrons similar to ammonia. This means that they can form salts with Lewis acids.
The basic strength of amines is weaker than that of hydroxide and alkoxide ions but stronger than that of water. –
R
NH2 + H2O
NH3]+ + OH
[R
[R NH3+] · [OH ] Kb = ––––––––––––––––––––– [R NH2]
–
The order of basic strength for amines is; As we have said, amines react with acids to produce salts.
Ammonium salts can be converted back into amines by heating with strong bases.
202
Oxygen And Nitrogen Containing Organic Compounds
4 A 500 mL solution of ethylamine is prepared by dissolving 0.1 mol of ethylamine in water. What is the pH of this solution? (K of ethylamine = 5 . 10–4) b
Even though many alkaloids (amines) are poisonous, some are used in medicine as analgesics (pain relievers) or anaesthetics, particularly morphine and codeine.
Molarity of 0.1 mol ethylamine in 500 mL solution; M
0.1 mol = –––––––––– = 0.2 mol/L 0.5 L C2H5
Initial
:
NH2 + H
0.2
OH
C2H5
M
Do You Know?
+ NH3
+ OH
––
–
Most alkaloids have a very bitter taste.
––
Change : – x + x M + x M –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Equilibrium : (0.2 – x)M (+ x) M (+ x) M +
–
[C2H5 NH3 ] [OH ] Kb = ––––––––––––––––––––––––– [C2H5 NH2] –
Then x = [OH ] = 1 · 10 –2 +
[H ] is 1 · 10 –12
M
x2 5 · 10 –4 = ––––––––– 0.2 – x If [H+][OH–] = 1 · 10 –14
M
+
pH = – log [H ] = – log 1 · 10–12 = 12
1.4. PREPARATION OF AMINES Reactions of ammonia with alkyl halides yield ammonium salts. Treating these ammonium salts with bases produces primary amines. If primary amines react with alkyl halides, secondary amines are produced. If the reactions are allowed to proceed, tertiary amines can be obtained. NH3 + R–X RNH2 + R–X
+OH–
RNH2 (primary amine)
+OH–
R2NH (secondary amine)
+OH–
R2NH + R–X
R3N (tertiary amine)
Almost all organic compounds containing nitrogen in their structure can be reduced to amines. Unsaturated nitrogen compounds (nitriles) can be reduced by the addition of hydrogen to give primary amines.
Amines, Amides And Amino Acids
203
5 Complete the following reactions.
Reduction of Amides Amides can be reduced to primary, secondary or tertiary amines by a strong reducing reagent such as LiAlH4.
a.
heat
b. C3H7Br + 2NH 3 C3H7NH2 + NH4Br c. The –NO2 group is converted to –NH 2
d. If amides are reduced by strong reducing agents the C=O bond is reduced to CH2.
e.
bonds in C N
C
CH3CH2
NH
C2H5 + H2O
N are broken and the group is reduced to
(CH2)4C
heat
N + 4H2 H2N
(CH2)6
CH2
NH2
NH2
2. AMIDES Amides are organic compounds derived from ammonia by replacing a hydrogen with an organic acid group. Hence amides may be defined as compounds containing a
204
Oxygen And Nitrogen Containing Organic Compounds
group.
Amides can be classified as primary, secondary or tertiary according to the number of alkyl groups attached to the –N atom.
2.1. NOMENCLATURE OF AMIDES 1. The simplest structure of amides is that in which the nitrogen is bonded to two hydrogen atoms. In order to name these, use the name of the carboxylic acid from which the amide is derived but replace the –ic or –oic suffix with –amide.
Amides are compounds in which the –NH2 group is attached to the carbon atom of an acid in place of the –OH group.
2. When naming secondary and tertiary amides, the groups attached to the (–NH2) group are indicated by the prefix N– , and these group names prefix the name of the corresponding primary amide .
2.2. PROPERTIES OF AMIDES Amides have hydrogen bonds between their molecules and so their boiling points are relatively high. For example, formamide is a liquid with boiling point 190°C while all other amides are white-crystalline solids. Since they are polar, they are water soluble. They do not react with acids and bases, though when heated slowly with water they are hydrolyzed.
2.3. PREPARATION OF AMIDES Amides can be prepared by the reaction of ammonia, primary amines or secondary amines with acid anhydrides, esters or acyl chloride.
Amines, Amides And Amino Acids
205
a. Acylation of primary amines leads to secondary amides.
b. Acylation of secondary amines produces tertiary amides.
Amides with an acyl group derived from acetic acid are called acetamides. Acetamides are generally produced from the reactions of acetic anhydride with amines.
206
Oxygen And Nitrogen Containing Organic Compounds
2.4. UREA (CARBAMIDE) Urea is colorless, water soluble and crystalline solid with a melting point of 132°C.
Urea is obtained from the reaction between CO 2 with NH 3 at high temperature and pressure. It can also be produced by the reaction of phosgene gas with ammonia.
It was first synthesized by Friedrich Wöhler in 1828 by evaporating a solution of ammonium cyanate. Urea is found in small amounts in the blood of mammals. Its principal industrial usage is in the manufacture of plastics (specifically, urea–formaldehyde resin) and is also a component of many fertilisers, providing a nitrogen source for plants.
3. AMINO ACIDS Amino acids contain both amino (–NH 2) and carboxyl (–COOH) groups in their
structure. Amino acids are the basic building blocks of proteins, which are the
basis of living organisms. There are over 700 naturally occurring amino acids.
The amino group in amino acids obtained from the proteins of plants and ani-
mals is in the position with respect to the carboxyl group.
An amino acid molecule contains both the amino and carboxyl group.
3.1. NOMENCLATURE OF AMINO ACIDS Amino acids are classified depending upon the relative positions of their functional groups. The following examples show the idea.
Amines, Amides And Amino Acids
207
3.2. PROPERTIES OF AMINO ACIDS Because of the existence of both (the –NH2) and (the –COOH) groups, amino acids display amphoteric properties (i.e., have both acidic and basic properties). They form metal salts when reacted with basic solutions.
But amino acids behave as bases towards acidic solutions.
Fish is an important source of protein.
In the solid state, amino acids exist as dipolar ions in which the carboxyl group is present as a carboxylate ion and the amino group is present as an aminium (NH3+) ion. This dipolar ion form of the molecule is known as a ZWITTERION.
Amino acids are linke d by peptide bonds. These bonds are formed by a dehydration synthesis reaction between the carboxyl group of the first amino acid and th e amino group of the sec ond amino acid.
4. PEPTIDE FORMATION AND PROTEINS Proteins are the largest and most complicated molecules that exist in the cells of living organisms. Proteins are polymers that are formed by many hundreds or even thousands of amino acid units. These units are bonded together by a peptide linkage. Peptides are amides formed by the reaction of amino groups with the carboxyl groups of amino acids. According to the number of amino acid units they are made up from, they are known as dipeptides, tripeptides or polypeptides.
208
Oxygen And Nitrogen Containing Organic Compounds
If the number of amino acids forming peptide bonds is “n”, (n–1) molecules of water are produced in the peptide formation.
If the number of amino acids forming polypeptide bonds is more than 12.000, the polypeptides are called PROTEINS. Although proteins contain only 20 kinds of amino acids, they can be arranged in many different sequences. Consequently, a small number of amino acids may form many different types of proteins. Proteins are used for repairing degenerated tissue in living organisms. DNA and RNA are also proteins.
The DNA helix is a protein.
CHEMISTRY OF VISION Have you ever wondered how vision occurs in our eyes? Many miraculous processes happen in our eyes. For good vision to occur, the retina of the eye must sense incoming light. A light image is in fact mapped onto the surface of the retina by activating
cis-retinal, it transforms into trans-retinal. Cis-retinal exists in a protein called rhodopsin. Trans retinal doesn’t fit into the protein and so a series of changes in the geometry of the protein begins. The new form bathrhodops in.
light sensitive cells called rods and cones.
of protein is During these
changes, the protein undergoes a large potential difference. This potential difference is picked up by a nerve cell as an electrical impulse. The nerve cell carries this impulse to the brain, where the visual information is encoded.
Vitamin A is transported to the rods in the retina from the liver, and here it is transformed into a substance called cis-retinal. The molecule cis-retinal can absorb light at a visible wavelength. When light strikes
Vitamin A
Light strikes
Cis–retinal
converts to
cis–retinal
converts to
cis–retinal
in rod cell
trans–retinal
Trans–retinal changes the shape
nerve impulse is
of rhodopsin to
carried to brain
bathrhodopsin
Amines, Amides And Amino Acids
209
1.
2.
Describe the general structures of amines, amides, amino acids, and proteins.
10. Name the following amides.
Name the following amines and give their types.
11. 5.95 grams of NH3 reacts with excess acetyl chloride
(CH3–CO–Cl). How many grams of acetamide are produced? (Cl : 35.5 g/mol, O : 16 g/mol, H : 1 g/mol, C : 12 g/mol, N : 14 g/mol)
3.
Write the structural f ormulae of the given amines.
a. cyclopropylamine b. dimethylethylamine c. ethylhexylamine d. methylethylisopropylamine
4.
What is the mass percentage of nitrogen in cyclopentylamine? (O : 16 g/mol, H : 1 g/mol, C : 12 g/mol, N : 14 g/mol)
5.
What is the f ormula of the alkyl in the primary amine of which 0.2 mole has a mass of 9 grams?
12. N-ethylacetamide is formed by the reaction of ethylamine and acetylamide. When 9 grams of ethylamine is reacted, how many grams of N-ethyl acetamide can be formed? 13. Compare the chemical properties of amino acids and amides. 14. Explain why amino acids are generally amphoteric compounds. 15. 0.2 M of 400 mL NaOH solution reacts with aminoacetic acid. What mass of salt is formed? (Na : 23 g/mol, O : 16 g/mol, H : 1 g/mol, C : 12 g/mol, N : 14 g/mol)
6.
Amines show weak basic properties when they are dissolved in water. Explain why?
16. Explain how peptide bonds are formed.
7.
[H+] is 10–12 M in 0.25 M propylamine solution. What is the Kb value of pr opylamine?
17. What is the difference between an amino acid and a protein?
8.
3.4 grams of NH3 reacts with 20.2 grams of CH3Cl. Find
18. What is the molecular weight of the dipeptide obtained from an amino acid of which 0.1 mole has a mass of 75 grams?
the formula of the amine formed by this reaction and name it. (Cl : 35.5 g/mol, O : 16 g/mol, H : 1 g/mol, C : 12 g/mol, N : 14 g/mol)
9.
What are the differe nces between amines and amides in terms of their structures?
210
Oxygen And Nitrogen Containing Organic Compounds
19. How many water molecules are formed when 100 amino acid molecules are bonded together by peptide bonds? 20. What is the importance of proteins in daily life?
1.
Some compounds and their types are given. Which pair
4.
are wrong?
that has a molecular weight of 45 grams?
What is the name of the alkyl group in the primary amine
A) Methyl
B) Ethyl
C) Propyl
D) Isopropyl
E) Aryl
5.
Which one of the f ollowing is not a secondary amine?
2.
I. CH3 – NH 2
II. CH3 – OH III. NH3 Which of the compounds above is (are) bas ic? A) I only
B) III only
D) II and III
C) I and III E) I, II and III
6.
3.
For an aqueous solution of the compound;
I. The pH > 7.
II. It conducts electricity.
III. It reacts with Zn metal to give H2 gas.
Which of the above compounds undergoes hydrogen
Which of the above statements is (are) correct?
bonding with itself?
A) I only
A) I only
B) II only D) II and III
C) I and II E) I, II, III
B) II only D) I and III
C) II and III E ) I, II and III
Amines, Amides And Amino Acids
211
7.
Which one of the f ollowing is a primary amide?
10. Which of the statements below is incorrect for 1 mole of acetamide and 1 mole of N-methylformamide?
A) Their carbon atom numbers are eq ual. B) The masses of their nitrogen atoms are equal. C) The number of their hydrogen atoms are equal.
D) They have different number of pi bonds.
E) They contain the same number of oxygen atoms.
11. An unknown organic compound forms a dipolar ion (a Zwitterion) and is optically active. Which one of the given compounds may be the unknown compound?
8.
Which statement is incorrect for
-aminoacids?
A) They are not optically active.
B) They contain two kinds of functional groups. C) They form Zwitterions in the solid state.
D) They are amphoteric.
E) They are slightly soluble in water.
12.
9.
For the above compound, which statement is correct?
Compound ——————— I. Amine II. III.
Functional Groups —————————— Nitro
Amide
Carbonyl, hydroxyl
Amino acid
Amino, carboxyl
A) It is named aminoethanoic acid.
Nitrogen containing organic compounds and their func-
B) It is optically active.
tional groups are given. Which description(s) is (are) cor-
C) It reacts with HCl.
rect?
D) It is neutral.
A) I only
E) It reacts with NaOH. 212
Oxygen And Nitrogen Containing Organic Compounds
B) III only D) II and III
C) I and II E) I, II and III
13. Peptide bonds; I. are formed between at least two amino acids.
15. Some compounds and the properties of their solutions are given below. Which pairing is incorrect?
II. are formed between nitrogen and carbon atoms. III. form Zwitterrions (dipolar ions).
Which of the above statements is(are) correct? A) I only
B) II only D) II and III
C) I and II
E) I, II and III
14. Which one of the following compounds is named incorrectly ?
Amines, Amides And Amino Acids
213
– C t
c
a
p
y
P
a
i t
c
p
i t
g
C
A These compounds are the basic building units of proteins, which are the basis of living organisms. These bonds are formed between two amino acid molecules. These are weak bases and organic derivatives of ammonia. They are also known as alkylated ammonia compounds. These are polyamides and the monomers from which they are derived are -amino carboxylic acids. They are found in all living cells. These compounds contain more than 12000 polypeptide bonds. If one alkyl group replaces one hydrogen atom in ammonia these type of amines are formed.
214
Oxygen And Nitrogen Containing Organic Compounds
D Two carbon containing amide. These are organic compounds derived from ammonia by replacing a hydrogen with an organic acid groups. Because of the existence of both (–NH 2) and (–OH) groups, amino acids show _____________ properties.
1. PHENOLS Phenols are compounds that have the general formula Ar– OH. In phenols, the carbon atom to which the –OH group is attached undergoes sp 2 hybridization, so in general, phenols display different properties to alcohols. Phenols, depending upon the number of – OH groups, can be classified as mono, di or triphenols. The simplest member of the phenols is phenol itself. The methyl phenols are known as cresol. Many phenol compounds may be extracted from coke by distillation.
Phenol is the raw material for the production of many substances, ranging from aspirin to plastics.
Phenols display acidic properties. Both phenols and alcohols contain the –OH and so they have similar properties to some extent , for example, they can both be converted into ethers and esters. However, in general, they show very different characteristics and must be classified as different families.
1.1. PHENOL
Pure phenol is a colorless, crystalline solid with a melting point of 43°C. It is
hydrated and turns red when exposed to air. It is soluble in water, like alcohols
Dilute solutions of phenol are used as antiseptics and disinfectants.
dye stuffs, aspirin and antiseptics.
and ethers. Phenol is a poisonous substance and contact with skin causes burns.
Phenol is widely used as a starting material in the manufacture of nylon, plastics,
Compounds having an –OH group attached to a polycyclic benzenoid ring are also phenols. They are known as naphtols or phenantrols.
In industry, phenol is obtained from coke by distillation though there are various ways of manufacturing phenol in laboratories. Chlorobenzene reacts with NaOH under high temperature and pressure to produce phenol.
216
Oxygen And Nitrogen Containing Organic Compounds
Phenol is more acidic than alcohols (but less acidic than carboxylic acids).
Indicating the relative positions of sub stituents on benzene ring
1. Phenol reacts with NaOH like carboxylic acids whereas alcohols do not, R R
OH + NaOH
alcohol
no reaction
base
COOH + NaOH
carboxylic acid
base
R
COONa + H2O
carboxylic acid salt
2. Phenol does not react with basic salts such as NaHCO 3 like alcohols. R
OH + NaHCO3
alcohol
R
no reaction
basic salt
COOH + NaHCO3
carboxylic acid
basic salt
R
COONa + CO2 + H2O
carboxylic acid salt
3. Phenol is converted into 2, 4, 6 – trinitrophenol by concentrated nitric acid in the presence of H2SO4 catalyst.
Aromatic Compounds
217
4. Phenol can be halogenated by halogens in their aqueous solutions or in a CS2 solvent.
Leo Hendrik Baekeland (1863 - 1944)
Leo Baekeland (November 14,
5. The most important reaction of phenol is its polymerization reaction with formaldehyde, which produces bakelite.
1863 – February 23, 1944) was a
Belgian born American scientist who invented bakelite.
Bakelite was made from phenol and
formaldehyde by heating them together in a pressure molding.
Prior to Baekeland, Adolf von Baeyer had experimented with this
substance but didn’t complete his
Radios, televisions and electrical due to its insulating and heat resist-
work.
insulators were made of bakelite
Electrical insulators are made from bakelite because of its insulating and heatresistant properties.
ant properties.
2. AROMATIC NITRO COMPOUNDS 2.1. GENERAL STRUCTURE
218
Oxygen And Nitrogen Containing Organic Compounds
The –NO2 group is a meta director. Thus, all other groups after the first –NO 2 group are attached to the ring in the meta position.
2.2. NITRATION The nitration of an aromatic ring, requires a mixture of concentrated sulfuric and nitric acids. This generates the nitronium ion, NO 2+. When benzene is added to this mixture at room temperature, mononitrobenzene is formed. Hydrogen atoms in an aromatic ring can only be substituted by a strong electrophile, such as NO2+. –
+
2H2SO4 + HO
NO2
+
–
+
NO2 + 2HSO4 + H3O nitronium ion
The yield of nitration depends upon the concentrations of the acids, temperature and the length of the nitration process. In the nitration process, a maximum of three nitronium ions (NO2+) can be attached to the benzene ring since the nitro group is a meta director. However attaching the third nitro group is very difficult. The existence of the –CH3 or –OH group on a benzene ring makes nitration easier.
Nitrobenzene Nitrobenzene is a yellow, oily liquid with a boiling point of 209°C and a characteristic almond smell. The vapor of nitrobenzene is poisonous and it is a carcinogen. Nitrobenzene is denser than water and insoluble in it, though it is a good
Nitrobenzene, when inhaled, damages the structure of hemoglobin.
polar solvent itself .
Nitrobenzene does not react with acids and bases. It can be reduced to aniline using the catalysts of Fe, Sn or Zn in acidic solutions.
Nitrobenzene and aniline are both widely used in the dye industry.
Aromatic Compounds
219
Dinitrobenzene is prepared by the direct nitration of nitrobenzene. This yields
m–dinitrobenzene.
It is a yellow, crystalline solid with a melting point of 89 °C. It is a slightly polar
Dinitrobenzene
substance, insoluble in water, but soluble in alcohol.
Specific atoms or groups on a ben zene ring give defined directions to any further atoms or groups attaching to the ring.
Ortho and para dinitrobenzene can be produced using alternative methods.
Trinitrotoluene Toluene is easily nitrated since it has an alkyl (–CH3) group attached to the benzene ring. It can be prepared by direct nitration of toluene with a mixture of nitric acid and sulfuric acid. The nitration mechanism is similar to that of the nitration of benzene. HNO3 + 2H2SO4
–
NO+ + H3O+ + 2HSO4 2
The explosive known as TNT is trinitrotoluene.
Trinitrotoluene is a crystalline solid that melts at 81°C. It is widely used as an explosive (TNT, tritol) in shells and bombs. It is not as sensitive to shock and friction as other explosives can be. 220
Oxygen And Nitrogen Containing Organic Compounds
1 Synthesize the following compounds from benzene.
a. o–nitrotoluene b. m–chloronitrobenzene
a. Methyl (–CH3) is a ortho-para director, and –NO 2 is a meta director. –CH 3 must be attached to the ring first to obtain an ortho structure.
b. We must obtain a meta compound. So a meta director must be first attached to the ring.
3. AROMATIC AMINO COMPOUNDS
Indigo is a dark blue, water soluble dye that has been in use for a long time. The picture shows first the indigo compound synthesized by Baeyer Laboratories in 1890.
Aromatic amines are generally produced by the reduction of nitro compounds. They have characteristic and pleasant odors. They are soluble in alcohol and ether but only slightly soluble in water. The basicity of aromatic amines is weaker than that of ammonia and aliphatic amino compounds. They form salts with strong acids.
3.1. ANILINE Aniline was first synthesized from indigo. Aniline is a colorless liquid with a boiling point of 184 °C. It has a specific odor and is poisonous. If exposed to sunlight for some time it oxidizes and its color turns to light yellow.
Aniline Aromatic Compounds
221
It forms acidic anilinium salts (phenyl ammonium) upon reaction with acids. +
C6H5NH2 + HCl aniline phenylamine
–
C6H5NH3 Cl
anilinium chloride phenyl ammonium chloride
Anilinium salts can be converted back to aniline by NaOH. +
–
+
–
C6H5NH3 Cl + Na OH
C6H5NH2 + NaCl + H 2O
anilinium chloride
aniline
Preparation There are two widely used methods to produce aniline.
1. Nitrobenzene is reduced to produce aniline. Aniline is a colorless liquid. However , the aniline used in industry has a light yellow color. Aniline and water form two layers when mixed together. Aniline stays below the water because its den sity is higher (left tube). Aniline can react with HCl solution since it is a weak base (middle tube). If a sufficient amount of HCl is added, a colorless anilinium chlo ride (C 6H5NH3+Cl – ) is formed (right tube).
The reduction is done using iron and water vapor in industry.
In the laboratory, instead of water vapor, acid is used.
While being reduced, nitrobenzene takes six electrons per molecule from the metal atoms. The electrical charge in the medium is balanced by the protons (H+) of the acid.
2. Aniline can also be produced by the reaction of phenyl halides with ammonia The anilinium ion (C 6H5NH3+ ) in anilinium chloride shows weak acid properties. If NaOH is added to anilinium chlo ride solution (left tube), the anilinium ions loses a proton to give aniline (middle and right tube) 222
under high temperature and pressure.
Oxygen And Nitrogen Containing Organic Compounds
4. AROMATIC ALCOHOLS Compounds that have a hydroxyl group attached to a chain on a benzene ring are called aromatic alcohols. These alcohols differ from phenols and show similar properties to aliphatic alcohols. The most important aromatic alcohols are benzyl alcohol and -phenyl ethyl alcohol.
4.1. BENZYL ALCOHOL This is the simplest member of the aromatic alcohols. It is isomeric with cresol.
Its oxidation products are benzaldehyde and benz oic acid, respectively. It is a colorless liquid with a pleasant odor and has a boiling point of 205 °C.
The benzyl alcohol structure contains both the aliphatic and aromatic groups. Although it is an alcohol, it dissolves in organic solvents and is only slightly soluble in water. It reacts with Na and K to produce H2 as phenols and cresols do. However, phenols and cresols are differentiated from benzyl alcohol by their reaction with NaOH. Esters of benzyl alcohols also have a nice, pleasant odor.
Preparation Benzyl alcohol is produced by the same general methods used for the production of aliphatic alcohols.
Aromatic Compounds
223
2 4.48 liters of H2 gas at STP is produced by the reaction of a 39 gram mixture of phenol and benzyl alcohol with Na metal. What is the mole percentage of benzyl alcohol in the mixture? (C6H5OH : 94 g/mol, C 6H5CH2OH : 108 g/mol)
4.48L nH = —————— = 0.2 mol 2 22.4 L/mol Reactions of phenol and benzyl alcohol with Na;
As it is seen, t otal mole number of H 2 gas x y —— + —— = 0.2 2 2 And masses of phenol and benzyl alcohol are 94 x and 108 y respectively. So total mass equation is written as 94 x +108 y = 39 Now, by using the above equations x and y can be calculated; –188 x /2
+
y /2 = 0.2
94 x + 108 y = 39 ———————————————— 14 y = 1.4 y = 0.1 mol x = 0.3 mol Then, the mole percentage of benzyl alcohol can be calculated. 0.1 mol ————— . 100 = 25% is benzyl alcohol. 0.4 mol 224
Oxygen And Nitrogen Containing Organic Compounds
5. AROMATIC ALDEHYDES Aromatic aldehydes are compounds in which the aldehyde functional group
is directly attached to the benzene ring. The simplest aromatic alde-
hyde is benzaldehyde. The other aromatic aldehydes show similar properties to benzaldehyde.
5.1. BENZALDEHYDE Benzaldehyde is a colorless liquid which boils at 179 °C and has a bitter almond
The seeds of almonds.
taste and smell. It is found in the seeds of almonds, plums and peaches together with glucose and HCN. It dissolves well in alcohol and ether and is slightly soluble in water. Benzaldehyde is similar to aliphatic aldehydes in many ways. It can be reduced by LiAlH4 to benzyl alcohol.
It is oxidized by acidic K 2Cr2O7 solution or alkaline KMnO 4 solution togive product being benzoic acid. Benzaldehyde is a weak reducing agent, it slightly affects Tollens’ reagent but does not react with Fehling’s reagent at all.
The seeds of peaches contain ben zaldehyde.
Preparation There are numerous industrial production methods for benzaldehyde.
1. Benzaldehyde can be produced by the oxidation of benzyl alcohol with air using hot V 2O5 as a catalyst.
2. Toluene can be chlorinated and the benzalchloride product hydrolyzed.
Aromatic Compounds
225
3 What mass of benzaldehyde can be produced from 64.4 grams toluene with 60% efficiency? (C : 12 g/mol, H : 1 g/mol, O : 16 g/mol)
C6H5CH3 = 92 g/mol
Molar mass of toluene
Molar mass of benzaldehyde
C6H5CHO = 106 g/mol
Moles of toluene m 64.4 g n = —— = —————— = 0.7 mol M 92 g/mol The reaction is;
From 0.7 mol of toluene, 0.7 mol benzaldehyde is produced, but since the efficiency is 60%, then, 60 0.7 . ——— = 0.42 mol of benzaldehyde produced. 100 Mass of benzaldehyde = M . n = 106 g/mol . 0.42 mol = 44.52 g
6. AROMATIC CARBOXYLIC ACIDS Aromatic compounds that have one or more carboxyl groups (–COOH) in their structure are called aromatic carboxylic acids.
Aromatic carboxylic acids have boiling points higher than 100°C. They are colorless solid substances with a crystalline structure. They show similar properties to aliphatic carboxylic acids but they are only slightly soluble in water due to the benzene ring. They are more acidic than aliphatic carboxylic acids as the benzene ring increases their acidic character. 226
Oxygen And Nitrogen Containing Organic Compounds
6.1. BENZOIC ACID This is a solid that melts at 121°C and is soluble in hot water, alcohol and ethers. It undergoes the same reactions as aliphatic carboxylic acids.
1. It forms benzoyl chloride upon reaction with PCl 3, PCl5 or SOCl2
2. It forms esters when reacted with alcohols, these products have a pleasant odor.
Preparation Primary and secondary alkyl groups (but not tertiary) directly attached to a benzene ring may be oxidized by KMnO 4.
If the carbon attached to the benzene ring is tertiary, no reaction occurs.
Aromatic Compounds
227
Benzoic acid can also be prepared by the hydrolysis of benz oylchloride and benzonitriles.
6.2. TEREPHTHALIC ACID Terephthalic acid, also c alled paraphthalic acid or 1,4–benzene dicarboxylic acid, is an aromatic dicarboxylic acid.
Dicarboxylic aromatic acids form polymers by reacting with dialcohols such as glycol. Polyethylene terephthalate can be obtained by a direct acid - catalyzed esterification. It is also known as Dacron, Terylene or Mylar.
228
Oxygen And Nitrogen Containing Organic Compounds
1.
Write out the structural formulae of the given compounds
a. nitrobenzene
10. Compare the boiling points of the isomers of dinitrobenzene.
b. o-nitrotoluene 11. Classify the following atoms and groups as ortho, meta or para directors.
c. m-dinitrobenzene d. 2, 4, 6 - trinitrotoluene
a. methyl (–CH3) b. chloro (–Cl)
e. 4-chloro-2,3-dinitrotoluene
c. ethyl (–CH2CH3)
d. amino (–NH2) e. nitro (–NO2) f. hydroxyl (–OH) 2.
Name the following compounds
12. Write out pounds.
the structural formulae of the given com-
a. aniline
b. diphenylamine
c. anilinium bromide
d. 2-amino-4-nitrotoluene
e. p-toluidine
f. methyl-diphenylamine
13. Name the following compounds
3.
What is the function of H2SO4 used in the nitration of benzene? Explain.
4.
When nitrobenzene is nitrated with nitric acid and sulfuric acid, to which position will the nitro group attach? Explain why?
5.
During nitration, what factors determine the number of –NO2 groups able to attach to the aromatic ring?
6.
Nitration of toluene is easier than that of benzene. Explain why?
7.
What is TNT? What is it used for?
8.
Calculate the molar mass of trinitrotoluene?
9.
Starting from benzene, how is p–bromonitrobenzene produced?
14. Compare the following compounds with respect to their basicity. I. P(OH)3
II. NH3
III. CH3NH2
IV. C6H5NH2
15. Which of the following compounds are solids at room temperature? a. nitrotoluene
b. m-dinitrotoluene
c. trinitrotoluene
d. aniline
16. Why can not the amino (–NH2) group be attached to the aromatic ring directly?
17. Prepare aniline starting from nitrobenzene. Balance your equation(s). Aromatic Compounds
229
18. 0.3 mol of 2,6–diaminotoluene is obtained by reducing 2,6–dinitrotoluene with iron dust. In this reaction;
27. Name the following compounds.
a. how many moles of 2,6–dinitrotoluene are used? b. how many grams of Fe dust are consumed? c. how many mL of 0.5
M
HCl solution are used up?
19. 100 mL of 0.5
M
H2SO4 is used to neutralize the aniline
obtained from 24.6 grams of nitrobenzene. Use this information to find the efficiency of the reduction reaction of nitrobenzene to aniline?
20. Write the reduction reaction of m-dinitrobenzene with Zn dust and HCl and name the products. 21. Define the phenol compounds. What are the differences between alcohols and phenols? 22. Write the structural formulae of the following compounds. a. phenol
b. m–cresol
c. 2,4,6–trichlorophenol
d. 2–bromo–5-methylphenol
e. m–bromophenol
f. pyrogallol
28. Write the structural formulae of the following compounds. a. benzyl alcohol b. p–methylbenzyl alcohol c. 1– phenyl–2–methyl–1–propanol d. m-trichloromethylbenzyl alcohol 29. What is the difference between benzyl alcohol and cresol? 30. A compound having the molecular formula C7H8O changes color in FeCl3 solution. When it is oxidized, benzoic acid is produced. What is the structural formula of this compound?
23. Name the following compounds.
31. Write the reaction equations of benzyl alcohol with the following substances and name the products. a. potassium
b. acetic acid (in H2SO4 medium) c. phosphorus trichloride (PCl3)
32. Starting from benzene, show how benzyl alcohol may be produced.
33. Name the following compounds. 24. Why does phenol show acidic properties?
25. Compare the given compounds with respect to their acidity. I. ethyl alcohol, II. water, III. phenol, IV. aniline
26. Which of the compounds, phenol, acetic acid and ethyl alcohol, react with NaOH but not with NaHCO3? 230
Oxygen And Nitrogen Containing Organic Compounds
34. Write the structural formulae of the following compounds.
41. Arrange the co mpounds in increasing order of acidity.
a. benzaldehyde
b. benzoyl chloride c. –phenylacetaldehyde d. –bromophenylacetaldehyde e. diphenylketone f. acetophenone 42. 35. Write two different production reactions to show how benzaldehyde can be formed from acetaldehyde.
I. HOOC(CH2)4COOH II. HOOC
C6H4
COOH
III. C6H11COOH Compare the compounds above with respect to their acidity.
36. Which of the following compounds oxidize(s) benzaldehyde to benzoic acid? Write the equations.
43. How could you differentiate between benzoic acid and phenol?
a. Acidic K2Cr2O7 solution b. Alkaline KMnO4 solution c. Tollens’ reagent
44. Explain why benzoic acid is a weaker acid than acetic acid.
d. Fehling’s re agent 45. 8.96 liters of O2 gas at STP are consumed in the catalytic oxidation of toluene to benzoic acid.
37. How many grams of benzaldehyde with excess Tollens’ reagent need to be used to precipitate 43.2 grams of Ag.
a. How many grams of toluene are used up in this reaction? b. How many milliliters of 0.4 are produced?
38. Starting from benzene, show all steps in the production of benzaldehyde. 46.
39. Write the structural f ormulae of the given compounds. a. benzoic acid
b. o–phthalic acid
c. terephthalic acid
d. salicylic acid
M
benzoic acid solution
40. Name the following compounds
What are the substances represented by X, Y and Z in the above reactions?
47. Which compound must be oxidized to produce ortho phthalic acid? Write the reactions. Aromatic Compounds
231
1.
How many sigma bonds are there in one molecule of nitrotoluene? A) 9
B) 10
C) 12
D) 15
5.
E) 17
Which one of the following is the incorrect name for the above compound? A) m-aminotoluene B) m-toluidine
2.
C) m-methylaniline
Which of the following processes is a reduction reaction?
D) m-aminomethylbenzene
A) production of aniline from nitrobenzene.
E) p-methylnitrobenzene
B) production of phenylchloride from benzene. C) production of nitrobenzene from benzene. D) production of benzoic acid from toluene. E) production of benzoic acid from benzaldehyde.
6.
Which one of the following groups cannot be directly attached to the benzene ring? A) –NO 2
3. I. C6H6 + Cl2
B ) – NH2
C) –OH
D) –Cl
E) –Br
AlCl3
II. C6H6 + Br 2 (aq) III. C6H6 + HNO3
H2SO4
7.
Which of the above reactions actually occur? A) I only
B) I and II D) I and III
Which one of the following compounds is an oxidation product of 2,6-dihydroxyaniline?
C) II and III
E) I, II and III
4.
How many grams of 63% by mass HNO 3 must be used to convert 27.6 grams of toluene to trinitrotoluene in the presence of H2SO4? (N : 14 g/mol, C : 12 g/mol, H : 1 g/mol, O : 16 g/mol) A) 60
232
B) 70
C) 80
D) 90
E) 100
Oxygen And Nitrogen Containing Organic Compounds
8.
How many mL of 0.8 M HCl solution is needed to neutralize the aniline that is produced from 49.2 grams of nitrobenzene with 25% efficiency?
12. Both phenol (C6H5OH) and ethanol (C2H5OH) can react with; I. Na metal
(N : 14 g/mol, C : 12 g/mol, H : 1 g/mol, O : 16 g/mol) A) 100
B) 125
C) 150
D) 250
II. HBr solution III. NaOH solution
E) 500
Which of the above s tatements is(are) c orrect? A) I only
9.
C) I and II
D) I and III
Which one of the following changes the color of litmus paper to blue?
B) II only E) II and III
13. Which of the combinations below shows the given compounds in order of increasing acidity? I. CH3COOH
II.
III. C6H5OH
10. 1 mol of which of the follow ing compounds can produce 2 mol of CH3COOH?
D) II > I > III
A) C6H5CH 2O H
Compound Preparation Method ——————— ————————————————— I. nitrobenzene nitration of benzene
III. phenol
E) III > I > II
B) C6H5OH
D) HOCH2CH2OH
15.
II. aniline
C) I = II > III
14. Which one of the give n compounds can react with Na, NaOH and NaHCO3?
11.
B) III > II > I
A) I > II > III
A Bromobenzene
C) CH3OH
E) C6H5COOH
phenylmagnesium bromide
B
benzyl alcohol
What are the reagents A and B?
reduction of nitrobenzene addition of base to benzylchloride
A ——————————— A) phenol
B ——————————— benzaldehyde / H 2O
Which of the preparation methods given above is(are) correct?
B)
magnesium bromide
acetone/HBr
C)
magnesium
formaldehyde/HBr
A) I only
D)
magnesium
acetaldehyde/H2O
E)
magnesium bromide
formaldehyde/HBr
B) III only D) I and III
C) I and II E ) I, II and III
Aromatic Compounds
233
16. When 1 mole of C7H8O reacts with Na, 0.5 mole of H2 and an unknown compound are produced. In addition,
20. Which one of the following is not an isomer of the others?
when it is oxidized, salicylic acid is formed. Which one of
the compounds below must be of C7H8O?
A) m–cresol
B) Benzyl alcohol
C) o-dihydroxybenzene
D) Phenol
E) Phenylmethyl ether
17. Benzaldehyde can react with; I. K2Cr2O7 /H+ II. Tollens’ reagent
21.
III. Fehling’s reagent
IV . LiAlH4
Which of the reagents above is(are) c orrect? A) I only
B) I and IV D) I, II and IV
C) I, III and IV
E) IV only Which one of the following statements is correct for the reactions given above? A) X is benzyl chloride. B) Y is an aromatic aldehyde. C) The first reaction is an oxidation reaction.
I. Phenol
18.
D) The second reaction is an addition reaction.
II. Benzoic acid
E) The molar mass of X is greater than that of Y.
III. Benzyl alcohol Which of the above compounds can react with at least two substances from K, KOH and KHCO3 ? A) I only
B) II only D) I and III
C) I and II E) II and III
22. Which one of the f ollowing is benzyl chloride?
19. How many liters of H2 are produced at STP when 200
grams of 5.4% by mass benzyl alcohol solution reacts with Na metal? A) 1.12 234
B) 2.24
C) 3.36
D) 4.48
E) 5.6
Oxygen And Nitrogen Containing Organic Compounds
23.
26. Which one of the statements given
below is wrong for the compound on
the right?
What are the substances X and Y in the above reactions?
A) It is a benzoic anhydride.
X ———————— A) Acetyl chloride
B) When 1 mole is hydrolyzed, 2 moles benzoic acid are
Y ———————————— Phenylmethyl ketone
produced. C) It is produced by the reaction of benzoic acid with
B) Acetic acid
Acetophenone
C) Acetyl chloride
Phenylmethyl ester
D) Benzoic acid
Phenylmethyl ketone
D) The pH value of its solution is less than 7.
E)
Acetophenone
E) When 1 mole reacts with 1 mole NH3, 1 mole ben-
Benzyl chloride
benzaldehyde.
zoic acid and 1 mole benzamide are produced.
27. The compound shown on the right can
be called; I. sodium-2-hydroxybenzoate II. sodium m-hydroxybenzoate
III. sodium salicylate
24. Which one of the f ollowing is the weakest acid?
Which of these names is (are) correct?
A) I only
B) I and II D) II and III
C) III only E) I, II and III
28. For the compound
I. CO2 is released when it reacts with NaHCO3. II. Phenol and bromoacetic acid are produced by its reaction with HBr. III. When it is hydrolyzed, benzyl alcohol and acetic acid
25. How many pi () bonds are there in one molecule of the compound that is produced by oxidizing o-xylene? A) 1
B) 2
C) 3
D) 5
E) 6
are produced. Which of the above st atements is(are) c orrect? A) I only D) II and III
B) I and II
C) I and III
E) I, II and III Aromatic Compounds
235
29. Which one of the following does not produce benzoic
32. Which one of the following compounds cannot be oxidized to benzoic acid?
acid when it is oxidized?
A) Toluene
B) Benzylalc ohol
D) Acetophenone
C) Benzaldehyde
E) Tert-butylbenzene
33.
is heated with alkaline KMnO4,
the product is then reacted with a strong acidic solution. Which product will be produce d by this process?
I. CH3COOH
30.
II. CH3CH(OH)CH3 III. C6H5OH
produce H2 gas?
A) I only
B) I and II
D) II and III
C) I and III E) I, II and III
31. Which one of the following compounds does not show
Compound ——————
34.
acidic properties?
Which of the above compounds can react with Na to
Oxidation Product ——————————
I.
Aniline
nitrobenzene
II.
Toluene
benzaldehyde
III.
p-xylene
terephthalic acid
Which of the above pairings are correct?
A) I only
B) I and II D) II and III
236
Oxygen And Nitrogen Containing Organic Compounds
C) I and III E) I, II and III
35. For the compound
38.
I. It is an alcohol.
II. It is an ester.
By which one of the reactions below may the above compound be formed?
III. It is a hydroxy acid. Which of the descriptions above are incorrect? A) I only
B) II only D) I and II
C) III only
E) I, II and III
36. For the compound;
I. It reacts with NaOH.
II. When it is oxidized, salicyclic acid is formed. III. It changes the color of aqueous Br2 solution. Which of the statements above is(are) correct? A) I only
B) I and II D) II and III
C) I and III E) I, II and III
39. Initial Substances ————————————
37. I. II. III.
Polymer Produced ——————————
Phenol-formaldehyde
Bakelite
Terephthalic acid-glycol
Dacron
Aniline-phenol
Acetophenone
Which of the pairings above are correct? A) I only
B) I and II D) II and III
C) I and III E) I, II and III
Which of the above compounds f orms a basic salt with NaOH and has an aqueous solution that is acidic? A) I only
B) I and III D) I and IV
C) IV only E) I, II and III
Aromatic Compounds
237
– C t
c
a
p
y
a
P i t
c
p
i t
g
C
A It is a colorless liquid with a boiling point of 184°C. It has a characteristic odor and is poisonous. If it is exposed to sunlight for some time it oxidizes and its color turns to light yellow. It is a colorless liquid that boils at 179°C and has a bitter almond taste and smell. It is found in the seeds of almonds, plums and peaches together with glucose and HCN. It is a dark blue, water soluble dye which has been in use for a long time. It was first synthesized by Baeyer’s Laboratories in 1890 . These are compounds having the general formula ArOH.
238
Oxygen And Nitrogen Containing Organic Compounds
D Compounds that have one or more carboxyl groups (–COOH) in their structure, are called aromatic _____________ acids. It is a heat-resistant compound. Electrical insulators are made from this because of its insulating and heatresistant properties. It is a crystalline solid that melts at 81°C. It is widely used in explosives. Polyethylene terephthalate.
GLOSSARY Alcohol : Compounds in which the hydroxyl group is
Benzaldehyde : C7H6O2, a colorless liquid.
bonded to an alkyl group. Carbohydrates : Polyhydroxyaldehydes or polyhydroxy Acetaldehyde (ethanal) : Colorless liquid with a characteristic odor. Acetic acid : Colorless liquid with a pungent irritating odor, CH3COOH. Acid anhydrides : Substances formed the elimination of one or more molecules of water from two molecules of an
ketones or substances that yield these by hydrolysis. They are obtained from plants or animals. Carbonyl group : A type of group containing carbon–oxygen double bond, Carboxylic acid : Organic compounds containing one or more carboxy (— COOH) groups.
acid. Cellulose : (C6H10O5)n. The chief constituent of the cell Acidic strength : The strength of an acid is measured by the value of its dissociation constant.
walls of all plants and the most abundant organic substance found in nature.
Aldehyde : Organic compounds with the carbonyl group
Chirality : A term which may be applied to any asymmet-
joined directly to another carbon atom.
ric object or molecule.
Alkaloid : Another name for amines.
Combustion reaction : The reactions in which reactants burn in an excess of oxygen to form carbon dioxide and
Amides : Organic compounds derived from ammonia by
water. These are exothermic reactions.
the substitution of a hydrogen atoms by an organic acid Dehydration reactions : The elimination of water from a
group.
larger molecule. Amines : Organic compounds derived from ammonia by the replacement of one or more of its hydrogen atom by hydrocarbon groups.
Detergents : Water-soluble, surface-active agents capable of wetting a variety of surfaces and removing greasy and oily deposits, retaining the dirt in suspension to be rinsed.
Amino acids : An important class of organic compounds containing both the carboxyl, — COOH, and the amino, — NH2 , group.
Aniline : C6H7N, a colorless oily liquid turning brown on oxidation.
Disaccharides : Carbohydrates that may be hydrolyzed to produce two monosaccharides molecules. Dextrins : Intermediate products formed during the hydrolysis of starch to sugars.
Azeotropic mixture : Mixtures of liquids when distilled
DNA : Deoxyribose nucleic acid. It is found in the nuclei of
reach a stage at which the composition of the liquid is the
all cells. It carries the necessary hereditary information that
same as that of the escaping vapor.
enables highly specific proteins to be constructed.
240
Oxygen And Nitrogen Containing Organic Compounds
Enantiomer : Stereoisomers whose molecular structures are non-superimposable mirror images.
Grignard reaction : When alkyl and aryl halides, particularly bromides and iodides, react with magnesium in the presence of dry ether to form compounds of the type
Esterification : Organic reactions involving the union of an acid and an alcohol with the elimination of water. Esters : Organic compounds formed by the union of an acid and an alcohol with the elimination of water. Ethers : Compounds in which both hydrogens of water are replaced by alkyl groups. Fats : Fats are esters of fatty acids and glycerol. Fatty acid : Long chained carboxylic acids produced by the hydrolysis of a lipid. Fehling’s solution : A solution of copper sulphate, sodium potassium tartrate and NaOH used for detecting reducing sugar and aldehydes. Fermentation : Carbohydrates are converted into simple sugars which are then, they are converted into alcohol and
RMgX where R represents the alkyl or aryl radical and X the halide. Hydrogenation : A specific method of reduction in which hydrogen is added to a substance directly. Hydrolysis : A term is used to signify reactions involving water as a reactant. Hydroxy acid : Carboxylic acids that contain ( — OH) hydroxyl groups. Indigo : C10H10N2O2 . A very important and long known dyestuff. Keto acids : Carboxylic acids that have the carboxyl group in their structure. Ketones : An organic compound containing the carbonyl group bonded to hydrocarbon groups.
carbon dioxide. Formaldehyde (methanol) : HCHO. A colorless gas with
Lactose : C12H22O11. Milk sugar, present in the milk of all animals.
a characteristic and pungent odor. Formic acid : A colorless liquid which fumes slightly and
Maltose : C12H22O11. A disaccharide that is present small quantities in barley grains and some other plants.
has a penetrating odor. Margarine : Manufactured food product used in place of Fructose : C6H12O6. Crystallizes in large needles. The most common ketose sugar. Glycerine (Glycerol) : The simplest trihydric alcohol. Glycogen : (C6H10O5) x . The carbohydrate reserve of the animal cell. Glycol : Alcohols containing two – OH groups are called glycols.
butter. Produced from vegetable oils and contains some polyunsaturated fats. Markovnikov’s rule : When a reagent containing hydrogen adds to an unsymmetrical double bond, hydrogen adds to the double bonded carbon atom that bears the greater number of hydrogen atoms. Monohydric alcohol : Alcohols containing only one hydroxyl group.
Oxygen And Nitrogen Containing Organic Compounds
241
Monosaccharides : Carbohydrates
that
cannot
be
hydrolyzed into smaller carbohydrates. Neutralization reaction : The reaction of an acid with a
RNA : Ribonucleic acid are found mainly in the cytoplasm. They are polynucleotides. Saccharose : (Sucrose) C12H22O11. Cane or beet sugar.
base. Saponification : The alkaline hydrolysis of an ester into an Nitrobenzene : C6H5NO2. A colorless, highly refractive
alcohol and alkali metals carboxylic acid salt.
liquid with a characteristic smell. Starch : (C6H10O5)n. This carbohydrate is being continuOptical isomers : Stereoisomers that rotate the plane of
ously formed and broken down in living cells and in an
plane polarized light.
energy reserve.
Optically active : The ability of a compound to rotate the
Terephthalic acid : C8H6O4. Crystallizes into colorless
plane of plane polarized light. Oxyacid : Organic acids that have a hydroxyl group as well as a carboxylic group. Peptide : Substances composed of two or more aminoacids. Designated as di–, tri–, oligo–, or poly– peptides according to the number of amino-acids linked by the peptide bond. Phenols : C6H6O colorless and crystalline and, miscible with water in all propontions. Photosynthesis : The process by which green plants build up their carbon compounds from atmospheric carbon
needles. It is manufactured by the oxidation of p-xylene and used in the production of terylene. The Williamson method: This method is used in the presence of a basic catalyst to produce both symmetrical and unsymmetrical ethers. Tollens’ reagent : An ammoniacal solution of silver oxide, used as a test for aldehydes and result in the deposition of a silver mirror on the inside of the reaction container. Trinitro toluene (TNT) : This important explosive is manufactured by the nitration of toluene in several steps, C7H5(NO2)3 .
dioxide and water using light as the energy source. Urea (Carbamide) : CH4N2O, (H2N)2 C=O. A colorless Polyhydric alcohol : Alcohols with two or more hydroxyl
crystalline solid. A weak base that forms salts with strong acids.
groups. Polysaccharides : Carbohydrates with a very high molecular weight (C6H10O5)n. Polysaccharide molecules can be
Wood alcohol : Methyl alcohol. It is prepared by the distillation of wood at high temperature.
hydrolyzed into hundreds of monosaccharide molecules. X rays : Streams of very high energy photons emitted by Proteins : A macromolecular substance found in cells consisting wholly or mostly of one or more polypeptides, often combined with another organic molecule or a metal ion.
242
Oxygen And Nitrogen Containing Organic Compounds
substances when bombarded with high energy electron beams.
Q Chapter_1 1.
ALCOHOLS AND ETHERS
16. 11.1 g
19. a. 2CO2 + 3H 2O
c. CH3OK + 1/2H2
d. C2H5OI + H2O
e. CH3CH2CHOHCH3 f. HCOOCH3 + H 2O
2.
k. 3CO2 + 12H2O
a. 2 – butanol c. 5 – methyl – 1 – hexanol
20. 87.5%
e. 3 – ethyl – 3 – pentanol
23. a. Ethoxy ethane, diethyl ether
g. 1,2,3 – propantriol
c. 2–isopropoxy propane, diisopropylether
i.
e. Cyclopentoxy cyclo pentane, dicyclopentyl ether
p – hydroxy benzyl alcohol
3.
III > I > II
4.
24.
6.
a. tertiary
b. secondary
c. secondary
27. 36%
11. C5H11OH
28. 60 g/mol b. ethylalcohol
13. C3H7COOH, 8.8 g 14. 66 g
25. CH3OCH3 26. 81.1%
10. 2.24 L
12. a. 46 g/mol
d. tertiary
35. a. C4H9 — O — C4H9, dibutyl ether 36.
33. a. Diethyl ether c. Methyl vinyl ether
37. I I > I > I V > I I I
34. a, d, e and f
Oxygen And Nitrogen Containing Organic Compounds
243
Chapter_2 1.
2.
ALDEHYDES AND KETONES
a. 2–chloro propanal c. 2,2–dichloro butanal e. 3–chloro butanal
6.
a. 3–methyl–3–phenyl butanal
b. 3,4–dihydroxo butanal
c. 3–methyl–4–bromo–2–butene–1–al
d. 2,2–dimethyl propanal
e. 6–cyano hexanal 3.
7.
a. C5H8O c. C7H5NO3 e. C6H12O3 f. C6H11BrO 5.
a. HCHO, formaldehyde, methanal b. CH3CHO, acetaldehyde, ethanal c. C2H5CHO, propionaldehyde, propanal
244
4.
Oxygen And Nitrogen Containing Organic Compounds
8.
a. Ethenal b. 2,2–dimethyl propanal c. 2–methyl butanal d. 2–methyl propanal
9.
75%
10. 58 g/mol 11. C5H10O 12. Aldehyde, ether and alcohol 14. I > II > IV > III 16. C2H5CHO, 58 g/mol 17. 14.08 g, CH3CHO 18.
b. CH3CHO
[O]
CH3COOH [O]
d. CH3CH2CHO
CH3COOH
19.
20. 20 g propanol 21.
22. X: C2H5Br Y: C2H5OH Oxygen And Nitrogen Containing Organic Compounds
245
23. 11 g of acetaldehyde CaC2
+2H2O
+H2O
C2H2 CH3CHO –Ca(OH)2
26. a. CH3CHO acetaldehyde b. 24.75 g 27. (COOH)2, 90 g/mol 28. a. 3–methyl–2–butanone (methyl isopropyl ketone) b. 4–hydroxo pentan–2–one c. Cyclopentanone d. 4–ethyl hexa–1,5–dien–3–one e. Diphenyl ketone 29.
30.
31. b. 2–propanone c. Propanal, CH3CH2CHO is isomer of acetone. Acetone has no isomer as ketone.
32.
246
Oxygen And Nitrogen Containing Organic Compounds
Chapter_3
CARBOXYLIC ACIDS
3.
a, b, f
5.
C3H5COOH
6.
a. Monocarboxylic acid – amino acid b. Dicarboxylic acid – hydroxy acid c. Dicarboxylic acid – oxyacid d. Monocarboxylic acid – keto and hydroxy acid
7.
11. a. Acetic acid c. Butyric acid
12. a. Ethanedioic acid b. 2–oxypentanoic acid c. 1,3–propandioic acid
16. II > I > III
23. a. 0.6%,
b. 1.8 · 10–5
24. pOH = 10.6
25. 0.36 mol
26. 0.025 8.
a. 2–chloro–5–methyl benzoic acid / m–chloro–o–methyl benzoic acid c. 4–chloro–3–methyl pentanoic acid / –chloro––methyl valeric acid
9.
27. A : CH3CH2Br B : CH3CH2CN
b. 2–methyl–1,5–pentandioic acid
C : CH3CH2COOH
d. 4–cyano–2–pentenoic acid 10.
M
c. Hydroxynitrile
31.
29. a. Acid anhydride
D :
Oxygen And Nitrogen Containing Organic Compounds
247
32.
45. 17.25 g
46. 107.25 g
48. a. 0.95%
49. 0.116 L
50. 115.94 mL
51. 0.3 mol
33.
b. 2CH3COOH + Mg(OH)2
H+
CH3COOC2H5 + H2O
e. CH3COOH + C2H5OH g. 3CH3COOH + PCl3 i.
CH3COOH + Cl2
(CH3COO)2 Mg + 2H2O
3CH3COCl + H3PO3 P
CH2COOH –HCl
I
Cl
C6H5COONa + 1/2H2 b. C6N5COOH + CH3OH C6H5COOCH3 + H 2O c. C6H5COOH + PCl5 C6H5COCl + POCl3 + HCl
34. a. C6H5COOH + Na
35. (C2H5COO)2 Mg 36. a. Acetyl chloride. 37.
b. Calcium acetate
41.
248
Oxygen And Nitrogen Containing Organic Compounds
52. 1568 ml
Chapter_4
ESTERS
3.
a. 120°C
7.
4.
a and d
8.
5.
a. methyl acetate
c. phenyl acetate
d. 2–bromo ethyl formate
e. 2–butenyl acetate
f. isobutyl methyl ester
h. isopropyl ester i. chloromethyl cyclopentyl ester
9.
6.
12. a. HCOOH + C3H7OH
13. b. C15H31COONa + C4H9OH
14. c. HCOO — CH2 — C6H5
f. C3H7COOC3H7 + H 2O
15. b.
23. 40 g 25. 2.76 g 27. a. C3H5(C17H33COO)3 + 3NaOH
18. 118 g/mol
17. II. CH3COOC2H5, 78 g/mol
16. CH3COOC3H7
3C17H33COONa + C3H5(OH)3
30. a. V, b. III, c. VI, d. I, e. II, f. IV
Oxygen And Nitrogen Containing Organic Compounds
249
Chapter_5 11.
CARBOHYDRATES
Chapter_6 AMINES, AMIDES AND AMINO ACIDS
b. trimethyl amine, tertiary d. methyl cyclopentyl amine, secondary
2.
3.
23. 14.3 g
22.
4.
16.5%
5.
7.
4 . 10–4
8.
sec – amine (CH3)2NH
24. 43.2 g 25. 90% 26. a. C6H12O6
10. b. N – methyl – N – ethyl acetamide d. butryramide (butanamide)
b. 180 g/mol 11. 20.65 g 12. 17.4 g 15. 7.76 g 18. 1482 g/mol 19. 99
250
Oxygen And Nitrogen Containing Organic Compounds
Chapter_7 AROMATIC COMPOUNDS 1.
19. 50%
34.
22.
8.
2.
a. o – methyl nitro benzene
d. 4 – bromo – m – dinitro chloro benzyl
23. a. dihydroxybenzene
227 g/mol
25. III > II > I > IV
c. m – methyl – p – nitrophenol
37. 21.2 g 10. para > meta > ortho
27. a. Benzyl alcohol b. Phenyl ethanol
12.
c. m – hydroxy benzyl alcohol
39.
d. 2 – phenyl – 2 – propanol
28.
40. c. 3 – hydroxy – 5 – methylbenzoic acid
d. 3 – chloro – m – phthalic acid 13. a. o – methyl aniline c. m – tert – butyl aniline 14. I I I > I I > I V > I
30. C6H5
CH2
OH
33. b. o – methylbenzaldehyde d. 2 – amino – 2 – chloro benzaldehyde
41. II > I > III 45. a. 24.53 g b. 665 mL
15. c. trinitro toluene 46. X : C6H5CH2OH 18. a. 0.3 mol b. 67.2 g
Y : H2O Z : HCl
c. 7200 ml
Oxygen And Nitrogen Containing Organic Compounds
251
C Chapter_1
ALCOHOLS AND ETHERS
Chapter_5
CARBOHYDRATES
1.
D
6.
A
11. B
16. D
21. A
1.
C
5.
D
8.
E
11. E
14. A
2.
E
7.
A
12. D
17. A
22. A
2.
D
6.
B
9.
A
12. E
15. A
3.
A
8.
C
13. B
18. A
23. C
3.
E
7.
E
10. D
13. C
16. B
4.
A
9.
C
14. B
19. C
24. E
4.
D
5.
E
10. B
15. B
20. B
25. E
Chapter_2
ALDEHYDES AND KETONES
Chapter_6 AMINES, AMIDES AND AMINO ACIDS
1.
B
7.
C
13. B
19. E
25. C
1.
E
4.
B
7.
A
10. D
13. E
2.
A
8.
A
14. C
20. A
26. E
2.
C
5.
D
8.
E
11. D
14. A
3.
A
9.
A
15. B
21. D
27. D
3.
C
6.
C
9.
D
12. B
15. E
4.
B
10. B
16. C
22. B
5.
C
11. A
17. E
23. E
6.
E
12. C
18. B
24. B
Chapter_3
CARBOXYLIC ACIDS
Chapter_7 AROMATIC COMPOUNDS
1.
D
8.
E
15. B
22. C
29. A
1.
E
10. B
19. A
28. A
37. B
2.
C
9.
E
16. B
23. B
30. E
2.
A
11. C
20. D
29. E
38. C
3.
B
10. B
17. A
24. E
3.
D
12. A
21. D
30. E
39. B
4.
B
11. C
18. C
25. C
4.
D
13. D
22. C
31. E
5.
B
12. A
19. E
26. E
5.
E
14. E
23. A
32. E
6.
D
13. C
20. A
27. E
6.
B
15. C
24. B
33. E
7.
B
14. E
21. B
28. C
7.
E
16. A
25. D
34. C
8.
B
17. D
26. C
35. D
9.
C
18. C
27. C
36. E
Chapter_4
ESTERS
1.
B
4.
A
7.
D
10. B
13. A
2.
E
5.
D
8.
C
11. C
14. C
3.
E
6.
E
9.
B
12. E
252
Oxygen And Nitrogen Containing Organic Compounds
Chapter_1
ALCOHOLS AND ETHERS
Chapter_3
CARBOXYLIC ACIDS
SOLVE AND FIT PUZZLE
DOUBLE PUZZLE
Chapter_2
ALDEHYDES AND KETONES
DOUBLE PUZZLE
Chapter_4
W O R D S E A R C H
ESTERS
Oxygen And Nitrogen Containing Organic Compounds
253
Chapter_5
CARBOHYDRATES
Chapter_7
CRISS – CROSS PUZZLE
CRISS – CROSS PUZZLE
254
Oxygen And Nitrogen Containing Organic Compounds
CRISS – CROSS PUZZLE
Chapter_6 AMINES, AMIDES AND AMINO ACIDS
AROMATIC COMPOUNDS
INDEX acetal, 75
calcium acetate, 97
ethyl chloride, 37
acetaldehyde, 83
calcium carbide, 44
ethyl isopropyl ether, 49
acetate ion, 116
Cannizaro reaction, 82
ethyl methyl ether, 48
acetic acid (see ethanoic acid)
carbohydrate, 176 – 178
ethyl methyl ketone, 85
acetamide, 206
carbon dioxide, 40, 126, 133
ethylene, 31
acetone, 97
carbonic acid, 126, 137
ethylene glycol (see glycol),
acetophenone, 87
carboxyl group, 108 – 112, 119, 135, 198
fat, 164 – 167
acetyl chloride, 210
carboxylate, 116, 124, 125
fatty acid, 162, 166
acetylene, 129
carboxylate salts, 116, 125
Fehling’s reagent, 71, 72, 180
acid halide, 155
carboxylic acid, 25, 26, 96, 109, 112, 161
fermentation method, 42, 43, 47
acrylic acid, 113, 130
carboxylic acid salt, 217
formaldehyde, 64, 65, 81 – 83
acrylonitrile, 131
carcinogen, 84, 219
formalin, 81, 82
acyl group, 119, 158
cellobiose, 186, 188
formate ion, 113
adipic acid, 132, 134
cellulose, 188, 190
formic acid, 108 – 114, 125 – 128
alcohol, 10 – 47, 75, 81
cellulose trinitrate, 190
fructose, 178, 181, 186
aldehyde, 64 – 84
chiral molecule, 138, 139
galactose, 178, 187
aldose, 177, 182
chlorobenzene, 216
glucose, 43, 178 – 190
aldotetrose, 177
chlorophyll, 176
glycerine, 47, 162 – 165
aldotriose,
citric acid, 137
glycerol (see glycerine),
aliphatic, 71, 108, 223
combustion reaction, 35, 78, 95
glycogen, 188, 189
aliphatic aldehyde, 64, 225
cresol, 216, 223
glycol, 45
alkanamides, 115
cyanohydrine, 76
Grignard reagent, 38, 39, 76, 92
alkanoates, 155
dacron, 228
hemiacetal, 75, 179
alkenes, 36, 124
dehydration, 29, 53, 208
hemiketal, 89
alkoxide, 22, 75 – 76
dehydrogenation, 81, 83, 96
hemoglobin, 219
amides, 204 – 206
detergent, 169
hydrocarbon, 15 – 18, 67, 74
amines, 198 – 204
dextrine, 189
hydrolysis, 47, 124 – 125, 158, 165, 188, 189
amino acid, 109, 198, 207 – 209
diethyl ether, 54, 201
hydroxy acid, 109, 122, 137
ammonia, 69, 82
dimethyl ketone, 97
indigo, 221
aniline, 202, 221 – 222
dinitrobenzene, 220
isopenthyl acetate, 156, 157
aromatic, 223, 225, 226
disaccharide, 186, 187
isopropyl alcohol, 20, 97
asymmetric carbon, 140
disinfectant, 42, 48, 82, 128
keto acids, 109
Baekeland, L.H, 222
D–Ribose, 177
ketone, 85 – 91
bakelite, 218
electrophile, 27, 219
ketopentose, 178, 185
Baeyer, A., 218, 221
enantiomers, 138 – 139
ketotetrose, 178
benzaldehyde, 68, 225 – 226
esterification, 25, 120, 154, 160
lactic acid, 136 – 138
benzoic acid, 113, 227
esters, 154 – 162
lactose, 186, 187
benzonitriles, 228
ethanal, 68, 69, 71
linoleic acid, 135
benzophenone, 87
ethanol (see ethyl alcohol),
linolenic acid, 135
benzyl alcohol, 223
ethanoic acid, 113, 128 – 130
lithium aluminum hydride, 74
benzyl phenyl ketone, 85
ethers, 47 – 54
Lucas reagent, 28, 29
Butlerov, A., 81
ethyl acetate, 156, 157
malic acid, 133, 137
butyl alcohol, 20
ethyl alcohol, 41, 43
malonic acid, 133
butyraldehyde, 68
ethyl benzoate, 157
maltose, 186 – 189
butyric acid, 109, 113
ethyl butanoate, 157
mannose, 178
177
Oxygen And Nitrogen Containing Organic Compounds
255
