CONTENTS I.Organic qualitative analysis (Scheme of organic analysis) II. Multistep synthesis (a). Benzoic acid – m- nitrobenzoic acid - Methyl m-Nitrobenzoate (b). Aniline -acetanilide- p-bromoacetanilide- p-bromoaniline (c). Synthesis of dibenzal acetone by Aldol condensation (d). Synthesis of methyl orange by coupling reaction.
III. Organic Estimations (a). Estimation of Aniline/ Phenol (b). Estimation of Ester (c). Estimation of iodine value of Ester (d). Estimation of Saphonification value of an oil/fat (e). Estimation of Glucose using Fehling Solution
INSTRUCTIONS Chemistry is a discipline based on observation. In lecture you will learn principles and theories and in laboratory you have opportunity to experience these principles and theories in practice. The following section presents some general guidelines. Making laboratory safety important.
Kindly follow the guidelines given below:
Laboratory aprons must be donned at all times in the lab and put up hair properly. Sandals, open-toed shoes and high heels are not permitted in the laboratory. Shorts or skirts cut above the knee are not permitted in the lab. Never wear cloth that hangs.
Kindly follow the general behaviour listed:
Strictly avoid the use of regional languages in the lab. No food or beverages will be permitted inside the lab. Always read the upcoming experiments carefully and thoroughly, being used to understand all of the directions before entering the lab. Be in and ready, promptly when the lab begins. Always read the labels of the reagents and never use a reagent from an unlabelled bottle. Never smell a chemical straight out of the container. Never pour a waste chemical into drain or put in the garbage. Never pick broken glassware with your bare hands, regardless of the size of the piece. Please place all broken glassware in the appropriate broken glassware bucket. Should any injury occur regardless of how minor it is report it immediately to the Lab tutors. Wash your hand frequently during the lab and definitely wash your hand twice at the end of the lab.
QUALITATIVE ORGANIC ANALYSIS SCHEME OF ORGANIC ANALYSIS The Scheme of Analysis may be divided into five parts 1. 2. 3. 4. 5.
I
Preliminary tests Detection of elements Detection of Characteristic groups Confirmatory tests Confirmation by preparing a solid derivative for identifying the organic compound.
Experiment Observation Preliminary tests 1. Colour and appearance of (a) Colourless the substance are noted (b) Yellow
2. Odour is noted
(c) (a) (b) (c) (d)
3. Solubility is noted (e) A little of the given (f) compound is shaken with the following solvents (a) Cold water soluble
(b) Sodium hydroxide
(c) Dil.Hydrochloric acid
Inference
Presence of hydrocarbon, aldehydes, ketones, acids esters etc. Presence of aromatic Brown or black nitrocompounds Pleasant fruity Presence of phenol or amine Fishy or Presence of ester ammoniacal Presence of amines Kerosene like Presence of hydrocarbon smell Presence of benzaldehyde of Bitter almond nitrobenzene smell Pungent Presence of halogen compounds Carbolic Presence of phenol
Presence of sugars, lower aliphatic alcohols, aldehydes, ketones and esters. Insoluble Presence of aromatic hydrocarbons, amines, phenols, higher aldehydes, ketones and Soluble in sodium esters. hydroxide and reappears as turbidity on adding Presence of acids or phenols. excess of dil. HCl. Soluble and reappears as Presence of amines turbidity on adding excess of NaOH solution
II. Detection of Elements. Lassaigne’s Test. A small piece of metallic sodium is melted in an ignition tube by gentle heating. Then small quantity of the substance is added. It is again heated gently to complete the reaction and then strongly. When the ignition tube is red hot it is plunged into distilled water taken in a china dish. The tube breaks and any residual sodium react with water. The broken ignition tube is ground well with the bottom of a boiling tube. The mixture is boiled well and filtered and the filterate is known as the sodium fusion extract. The following tests are done with the extract. 1
2
To one portion of the sodium fusion extract half of its volume of freshly prepared ferrous sulphate solution is added, boiled, few drops of ferric chloride solution is added and acidified with dil hydrochloric acid Another portion of the extract is acidified with dil. Nitric acid, boiled well, cooled and silver nirate solution is added
A blue or green colouration Nitrogen is present or precipitate is obtained
(a) White curdy precipitate Chlorine is present soluble in ammonia (b) Yellowish white Bromine is present precipitate sparingly soluble in ammonia (c) yellow precipitate Iodine is present. insoluble in ammonia
3. To the third portion of the extract a few drops of freshly prepared Violet colouration sodium nitroprusside solution is added
Sulphur is present.
III DETECTION OF CHARACTERISTIC GROUPS 1
Test to find whether aliphatic or aromatic (i)Ignition test. A small quantity of (a) Burnt with a non-smoky the substance is ignited on nickel flame spatula (b) Burnt with a smoky luminous flame (ii) Nitration test: A little of the substance is added to a mixture Colourless solution containing 2mL con. Sulphuric acid and 1mL con. Nitric acid taken in Yellow solution test tube. It is then heated on a precipitate boiling water bath for about half an hour and then poured into cold water taken in the beaker
2
Test to find out whether unsaturated or saturated (i) Action of dilute potassium (a) Immediate permanganate: A little of the decolourisation substance is shaken with water and
Presence of aliphatic substance Presence of aromatic substance
Presence of alphatic substance or Presence of aromatic substance.
Presence of unsaturated compound
one or two drops of dil. potassium (b) Slow decolourisation permanganate solution
(ii)Action of bromine water: A little of the substance is dissolved in suitable solvent( alcohol/ water) then a little bromine water is added (iii) Action of bromine in carbontetrachloride: A little of the substance is dissolved in carbon tetrachloride and bromine in carbon tetra chloride is added and shaken
3
4
Presence of easily oxidizable substance like phenol, niro phenol, amines, belnzaldehyde, etc.
Decolourisation without the Presence of unsaturated compound. formation of a precipitate. Presence of saturated No decolurisation compound. of (a) Decolourisation without Presence unsaturated substance the evolution of hydrogenbromide (b)Decolourisation with the Presence of saturated evolution of hydrogen substances bromide (c) Decolourisation with Presence of easily brominated formation of a precipitate. compounds like phenols, aromatic amines etc.
Action of con. Sulphuric acid: A (a) Charring with little of the substance is warmed effervescence due to the with con.H2SO4 liberation of sulphurdioxide, carbondioxide, carbonmonoxide and smell of burnt sugar (b) dissolves gradually on heating (c) White precipitate which dissolved in excess of acid (1) Action of sodium hydroxide (a) Ammonia is evolved solution: A little of the substance is boiled with dilute (b) substance dissolved sodium hydroxide solution
Presence carbohydrate
of
Presence of aromatic hydrocarbon Presence of basic substance like aromatic amines Presence of amide
Presence of acidic substances like acids phenols and their derivatives (c)Separation of oil or Presence of anilides formation of an emulsion Presence of (d)Solution turns yellow in colour
deep nitrophenols
5
6
7
8
(2)The given compound is boiled with 20% sodium hydroxide for half an hour then cooled and acidified with dilHCl Action of Sodalime: A little of the substance is mixed with thrice its mass of dry sodalime in a dry test tube and heated. The smell of the issuing gas is noted. Action of sodium bicarbonate: to one mL saturated solution of sodium bicarbonate solution little of the substance is added Action of Metallic Sodium: To a little of the substance ( if solid dissolve in dry benzene) in a dry test tube a small piece of metallic sodium is added Action of ferric chloride solution: To a little of the substance in Water or alcohol a few drops of neutral ferric chloride is added
Action of Borsche’s reagent: To one mL of Borsche’s reagent a little of the substance is added and heated over a water bath for five minutes. Cooled and little water is added 10 Action of Schiff’s reagent: A little of the substance is added to 1mL Schiff’s reagent taken in test tube and shaken well 11 Action of Tollen’s reagent: A little of the substance is added to about 2ml tollen’s reagent in a clean test tube and heated in a boiling water bath
Presence of aromatic esters and amides
White precipitate
(a) Ammonia gas is evolved (b) Kerosene lie smell Brisk effervescence carbondioxide
Presence of amides and amines Presence of acids
of Presence of acids
Brisk effervescence
Presence of alcohols, acids and phenols.
(a) Violet colour (b) A flocculent white precipitate (c) green colour changing to a white precipitate (d) Buff coloured precipitate
Presence of phenol Presence of αnaphthol Presence of βnaphthol Presence of benzoic acid, cinnamic acid or phthalic acid
9
A yellowish orange Presence of aldehydes precipitate is obtained or ketones
Violet colour developed Presence of aldehydes within two minutes (a) Black or brown precipitate (b) Bright silver mirror is formed
12 Action of Fehling’s solution: Fehling’s solution A and Fehling’s solution B are mixed in equal Reddish brown precipitate is volumes. To 1 mL of this reagent a formed little of the organic compound is added and heated on a boling water bath
Presence of polyhydric phenol Presence of aldehydes, reducing sugars such glucose, fructose, maltose etc.
Presence of aldehydes, polyhydric phenols, and reducing sugars.
13 Action of Molish’s reagent: To a solution of substance in water added a few drops of alcoholic solution of Violet ring is formed at the Presence of α-naphthol. Then added about 1mL junction Carbohydrates. of con.H2SO4 along the sides of the test tube without disturbing IV Confirmatory Tests A If nitrogen is present is present, the following tests are conducted. Besides the following tests for those groups for which indications are got are also done. 1
2
3
4
5
Action of sodium hydroxide solution. A little of the substance heated with sodium hydroxide Action of Soda-lime: A little of the organic substance is heated with excess of dry soda-lime
(a) Ammonia is evolved Presence of amides (b)Separation of oil and Presence of anilides formation of an emulsion (a) Ammonia is evolved Presence of amides and amines (b) Amine is roduced Presence of aminoacids, toluidines and anilides Biuret test:A little of the substance A violet colour is produced. Presence of diamide is gently heated in a dry test-tube like urea. until it melts and then solidifies. The residue is dissolved in a little water and a dilute solution of copper sulphate is added followed by sodium hydroxide solution drop by drop. Action of nitrous acid: A little of (a) Liberation of nitrogen Presence of aliphatic the substance is dissolved in dilute with the formation of primary amines. hydrochloric acid, cooled in ice alcohol. water and a 10%solution of sodium (b) Separation of yellow oil. Presence of secondary nitrite is added with shaking till it is amines slightly in excess. (c) Reddish brown solution Presence of tertiary is obtained. amines With the solution obtained above the following tests are done. (i)To one portion of the solution an A scarlet red precipitate is Presence of aromatic alkaline solution of β-naphthol is formed. primary amines. added. (ii)A portion of the solution is Blue or green solution is Presence of secondary extracted with ether. The ether obtained. amines. extract is washed with sodium hydroxide solution and then with water. The ether is evaporated off and Liebermann’s nitroso reaction is conducted with the residual oil. (iii)To another portion, dilute Ether layer becomes deep Presence of tertiary
6
7
8
sodium hydroxide solution is added and then shaken with little ether. Carbylamine reaction. To a little of the substance few drops of cholorofm and about 2ml of alcoholic potash are added and warmed. Mulliken and Barker’s reaction. A little of the substance is dissolved in alcohol. A few drops of calcium chloride solution is added and pinch of zinc dust. Boiled for five minutes, cooled and filtered into a tube containing Tollens reagent. Reduction of nitro group to amino group. A little of the substance is treated with few ml of dilute hydrochloric acid and a pinch of zinc dust. Heated for some time and filtered. With the filtrate the following tests are done. (a) Carbylamine test is done with one portion of the filtrate (b) To another portion of the filtrate dil. hydrochloric acid is added, cooled in ice and sodium nitrite solution is added in excess. Then alkaline β-naphthol solution is added
green.
amines.
Offensive smell is produced
Presence of primary amine
Bright silver mirror or black Presence precipitate is obtained. group.
of
nitro
An offensive produced
of
nitro
A scarlet obtained
smell
precipitate
is Presence group
is Presence of aromatic nitro group.
B If halogen is present, the following tests are conducted. Besides the following tests, tests for those groups for which indications are got also done 1
Action with litmus. A little of the (a) soluble and acidic to substance is shaken with hot water litmus and tested with litmus (b) Insoluble and acidic
(c) Insoluble and neutral
2
Action with silver nitrate solution. A little of the substance is boiled with sodium hydroxide solution for (a) Precipitate of silver 15 minutes. Cooled, acidified with halide is formed dil. nitric acid and then added silver (b) No precipitate of silver
Aliphatic halogen substituted acids Presence of aromatic halogen substituted acids Presence of halogen substituted hydrocarbons, ketone etc.
Halogen is in the side chain Halogen is in the
3
nitrate solution. Action of alcoholic silver nitrate. To a little of the substance 2 ml of alcoholic silver nitrate solution is added and warmed gently.
halide (a) Precipitate of silver halide is obtained (b) No precipitate of silver halide
nucleus Presence of halogen in the side chain Presence of halogen in the nucleus.
C If sulphur is present, the following tests are conducted. Besides the following tests, the tests for those groups which indications are got also done. 1
2
3
Action of alcoholic sodium hydroxide To a little of the substance 2 ml of alcoholic sodium hydroxide solution is added and warmed gently. Action of con. Hydrochloric acid. To a little of the substance 2 ml con. HCl is added and warmed gently. Fusion with alkali. A little of the substance is fused with sodium hydroxide dissolved in water anf hydrochloric acid is added
Ammonia is evolved
Presence of thiourea or sulphonamide
Pungent smell
Presence of substituted thiourea.
(a) Hydrogen sulphide is Presence of thio urea evolved (b) Sulphurdioxide is evolve Presence of sulphonic with the formation of phenol acid (c) No phenol is formed but precipitate of barium Presence of amino sulphate when barium sulphonic acid chloride is added (d) Ammonia is evolved during fusion. No phenol is Presence od formed. Sulhur dioxide is sulphonamide evolved on adding acid D. If nitrogen, halogens and sulphur are absent, tests for the following groups for which indications are got, are done. I.Aldehydes 1. 2
3
4
Schiff’s reagent test is Violet colour is obtained conducted Borsche’s reagent test is A yellow precipitate is obtained. conducted. Note: Ketones also answer this test. Tollen’s reagent test is Bright mirror or black conducted. precipitate is obtained. Note: Other reducing reagents also answer this test. Fehlling’s solution test is Red precipitate is obtained. conducted. Note: Other reducing reagents also
Presence of aldehydes. Presence of aldehydes.
Presence of aldehydes.
Presence of aldehydes.
5
6
answer this test Sodium bisulphite test is conducted: A little of the substance is added to a saturated solution of sodium bisulphite and shaken well. Note: ketones also answer this test. Semicarbazide test: Dissolved 0.5g of semicarbazide hydrochloride in 5ml of water and added 0.5g of anhydrous sodium acetate. It is warmed to get a solution. Then added a small quantity of the substance and warmed on a water bath. Note: ketones also answer this test.
White crystalline precipitate Presence of aldehydes. is obtained.
White crystalline precipitate Presence of aldehydes. is obtained.
II. Ketones. 1
Borsche’s conducted.
reagent
test
2
Semicarbazide test is conducted.
3
Sodium bisulphate conducted.
4
Iodoform test is conducted: 0.25ml Yellow precipitate with Presence of ketones of acetophenone is taken in a test characteristic odour is containing the CH3-COtube.Add 1.5ml of NaOH solution formed group followed by I2-KI solution until the iodine colour persisted on shaking. The solution is warmed. Excess of iodine solution is removed by adding dil.NaOH solution drop by drop.The contents is allowed to stand in the water bath for 20minutes.
test
is A yellow precipitate is Presence of ketones. obtained. White crystalline precipitate is obtained is White crystalline precipitate
Presence of ketones. Presence of ketones
III.Acids 1 2 3
Tested with sodium bicarbonate Effervescence Presence of acids. solution. Sodalime test is conducted Kerosene smell Presence of acids. obtained Ester formation test is conducted. Pleasant fruity smell. Presence of acids. About 0.5g of the substance is heated gently with about 1 ml of
ethanol and few a drops of conc.sulphuric acid for about 1 minute. Cooled and poured into a few ml of water in test-tube.
4
5
s-Benzylthiouronium salt test: About 0.25 g of the acid is dissolved in 2 ml of warm water. The acid is neutralised by adding a few drops of NaOH solution (phenolphthalein can be used as an indicator) .Then 2 drops of NH4Cl are added followed by 0.5 g of sBenzylthiouronium chloride in 2ml water. It is cooled in ice. Fluorescein reaction. Fused together in a dry test-tube a small quantity of the substance with an equal amount of resorcinol after moistening the mixture with two drops of conc. Sulphuric acid. Cooled, dissolved in water and then added excess of sodium hydroxide solution.
White crystalline Presence of acids precipitate.
A reddish solution Presence of dicarboxylic having an intense green acids. fluorescence is produced.
IV.Phenols 1
2
3
Neutral ferric chloride solution test is (a) Violet blue or green colour. conducted. A little of the substance is treated with neutral ferric chloride (b) A flocculent white solution. precipitate.
Presence of phenol.
Presence ofαnaphthol. Liebermann’s nitroso reaction: To Red solution which turned to Presence two drops of melted phenol, added green or blue on adding phenol. little solid NaNO2 . Heated gently for sodium hydroxide solution. 1 minute.Cooled and added 4 drops of conc.H2SO4. Diluted cautiously with water. Phthalein fusion reaction: About 2 Red, bluish-purple, blur green Presence drops of melted phenol is mixed with fluorescene, green or very faint phenol. a small quantity of phthalic green colouration. anhydride in a dry test-tube. 2 drops of conc.H2SO4 are added. The mixture is heated at about 150oC for 2 min.Cooled and exess of 10 %
of
of
4
5
NaOH solution is added. Benzoylation (Schotten Baumann reaction) is conducted :Dissolved about 0.25 g of phenol in about 5ml of 10 % NaOH solution contained in a boiling tube . About 1 ml of benzoyl chloride is added. The boiling tube is corked and shaken vigorously for about 15 min. Azo-dye formation reaction: Dissolved 2 drops of aniline in 1 ml dil. HCl and well cooled in ice. A few drops of saturated NaNO2 solution are added. The diazonium solution thus obtained is added to a well cooled solution of phenol in aqueous NaOH solution.
Crystalline white precipitate.
Presence phenol.
of
Orange, scarlet,dark red, Presence brownish red solution or phenol. precipitate is obtained.
of
V. Alcohols. 1 2
Test with metallic sodium is conducted. Brisk effervescence. Presence of alcohols. Acetylation test: A little of the substance Pleasant fruity smell Presence of alcohol. is heated with glacial acetic acid and few is produced. drops of conc. Sulphuric acid. Then cooled and poured into excess of water containing little sodium carbonate solution.
VI. Esters. 1
2
Hydrolysis. A little of the substance is refluxed with concentrated solution of sodium hydroxide and then acidified with conc. Hydrochloric acid. Hydroxamic acid formation. To a few drops of the substance, added 0.2g of hydroxylamine hydrochloride and about 5 ml of 10% sodium hydroxide solution and the mixture gently boiled for 2 minutes. Cooled and acidified with dilute hydrochloric acid and then added a few drops of ferric chloride solution.
White precipitate is Presence of ester. formed.
A violet or a deep red- Presence of ester brown colour developed immediately
VII Carbohydrates. 1
Concentrated sulphuric acid test is Charring with smell of conducted. Warmed a little of the burnt sugar substance with conc. Sulphuric acid.
Presence of carbohydrate.
2
3
Sodium hydroxide test is conducted. A little of the substance is boiled with sodium hydroxide solution Molisch’s test is conducted.
4
Treated with Tollen’s reagent
5
Fehling’s solution test is conducted: Warmed with Fehling’s solution. Osazone test is conducted: About 1 g of sugar is dissolved in 15 ml water and add 4 g of phenyl hydrazine hydrochloride, 4 g of sodium acetate and 1 ml glacial acetic acid. Heated for 15 minutes in a water bath.
6
Solution turned yellow or brown. Caramel smell is emitted A deep violet ring is formed. Bright silver mirror or black precipitate.
Presence of carbohydrate.
Red precipitate is formed. Yellow crystals are formed.
Presence of reducing sugar. Presence of carbohydrate.
Presence of carbohydrate. Presence of reducing sugar.
VIII. Hydrocarbons. 1 2
3
4
Odour is noted.
Kerosene like smell Presence of observed. hydrocarbons. Sulphonation is conducted : To 1 ml of Substance has gone Presence of fuming H2SO4 contained ina test tube, 2 into solution. hydrocarbon. drops of the substance are added and shaken well for 3 min. Nitration is conducted. Note.(1) To nitrate naphthalene, about 0.5g of naphthalene is dissolved in 2 ml of glacial acetic acid by gently warming, cooled and heated to 800c after adding conc. Nitric acid. It is then poured into water when yellow crystals separate. Picrate test is conducted : Saturated solutions of naphthalene and picric acid, both in benzene are prepared separately. These two solutions are mixed in a watch glass and allowed to evaporate.
Yellow solid obtained.
Presence of hydrocarbon is confirmed
Red or yellow precipitate.
Presence of polynuclear hydrocarbons.
5. Confirmation by preparing a solid derivative The final step in the analysis of a sample organic compound is the preparatioof a suitable solid derivative.
Preparation of Derivatives Derivatives for Aromatic Hydrocarbons. The main reactions carried out for the preparation of derivatives for aromatic hydrocarbons are (a) nitration (b) side chain oxidation and (c) preparation of picrates for polynuclear hydrocarbons. (a) Nitration. Nitroderivatives can be prepared for benzene, toluene etc. About 1 ml of fuming nitric acid and 1 ml of conc.sulphuric acid are mixed.About 0.25 ml of benzene or toluene is added to the nitrating mixture. Then the mixture is heated on a boiling water bath for half an hour,till a drop of mixture poured into water crystallizes immediately. The mixture is then poured into cold water taken in beaker and stirred well. The crystals are filtered at the pump,recrystallised from dilute alcohol, dried and then melting point is noted. (b). Side chain oxidation. For aromatic hydrocarbons containing side chain like toluene or side chain like xylenes, side chain oxidation can be effected for the preparation of their derivatives. About 0.25 ml of the substance is mixed with about 12.5 ml of saturated potassium permanganate solution and 1 g of anhydrous sodium carbonate. The mixtutre is then boiled for half an hour under reflux. It is then transferred to a beaker, acidified with conc. Hydrochloric acid and then added a saturated solution of sodium sulphite until the brown precipitate of manganese dioxide has dissolved. It is cooled, filtered at the pump and recrystallised from hot water. It is dried and melting point is noted. (c) Picrates. Picrates can be easily prepared for polynuclear hydrocarbons like naphthalene anthracene ctc About 0.25g of picric acid is also dissolved in hot benzene. About 0.25g of picric acid also dissolved in hot benzene. These two solutions mixed well, poured into a watch glass and kept for sometime. Coloured crystals of picrate separate. Melting point is noted. Derivatives for Halogen compounds of Aromatic hydrocarbons. (a) Nitration. For compounds having halogen in the nucleus like chlorobenzene, ortho-chloro toluenes, para-dichlorobenzene etc. nitroderivatives are prepared. Nitration is carried out in the same manner as aromatic hydrocarbos. Melting point is noted. (b) Side chain oxidation. For compounds having halogen in the side chain like benzyl chloride and for nuclear halogen compounds containing side chain oxidation can be adopted.Side chain oxidation can be adopted exactly in the same manner as explained under aromatic hydrocarbons. Melting point of the derivatives is found out. Derivatives for alcohols. The following derivatives can be prepared for alcohols.(a) benzoates and (b) oxidation products. (a) Benzoylation(Schotten- Baumann reaction). About 0.25 g of the substance is dissolved in about 4 ml of 10% sodium hydroxide taken in a boiling tube. About 0.5 ml benzoyl chloride is added, corked the tube well and shaken vigorously for about 15 minutes.. (till the smell of benzoyl chloride is no longer perceptible). Filtered, washed several times with water. Dried and then recrystallised from alcohol. Melting point is determined. (a) Oxidation. Side chain oxidation can be carried out in the case of alcohols like benzyl alcohol. It is same as in the case of aromatic hydrocarbons Derivatives for phenols. The following derivatives can be prepared for phenols. (a) benzoyl derivatives (b) bromination products (c) Nitration products and (d) picrates (a) Benzoylation. Benzoylation can be easily carried out for phenols, cresols, α- naphthols, βnaphthols and resorcinol. Details of benzoylation, refer under the derivatives of alcohols. (b) Bromination. Bromination can be done in the case of phenols and cresols. A bout 0.25 g of phenol is treated with saturated bromine water till the yellow colour due to excess of bromine persists. The mixture should be shaken well after each addition of bromine water. The
crystallized bromo derivative is filtered at the pump, washed with water and dried. It is recrystallised from alcohol, dried and melting point is determined. (c) Nitration. Poly nitro derivatives can be prepared for certain phenols. About 0.25 g of phenol is dissolved in about 1 ml of cold conc. Sulphuric acid and the solution poured slowly into about 6 ml of the nitrating mixture, containing equal volumes of concentrated nitric acid and sulphuric acids. Then it is warmed for a few minutes on a water bath. If the reaction is violent and there is tendency to form tarry matter, it has to be cooled in ice without warming on the water bath. Cooled poured into ice water, filtered and recrystallised from dilute alcohol containing a few drops of conc. Hydrochloric acid. (d) Picrates. Picrates can be easily prepared for phenols. Details refer under derivatives of hydrocarbons. Derivatives for aldehydes and ketones. The important derivatives for aldehydes and ketones are: (a) Phenyl hydrazones(b) 2,4- dinitrophenyl hydrazones (c) semicarbazone and (d) oximes. (a) Phenylhydrazones. A solution of phenylhydrazine is prepared by dissolving 0.5g of phenylhydrazine hydrochloride and 0.75 g of sodium acetate in 5 ml of water. About 0.25g of aldehyde or ketone is dissolved in a little of alcohol and added to phenyl hydrazine solution. If a clear solution is not obtained, more alcohol is added. The mixture is heated on a water bath for about half an hour. The phenyl hydrazone is separated on cooling. It not a few drops of water are added. The product is filtered off and crystallized from alcohol. The melting point is determined. (a) 2,4- dinitrophenylhydrazones. Benzaldehyde acetophenone and benzophenone readily form 2,4- dinitrophenylhydrazones with 2,4- dinitrophenyl- hydrazine.(Borsche’s reagent). About 0.25 g of substance is diossolved in methanol. It is mixed with about 1 ml of Borsche’s reagent and shaken vigorously for a few minutes, with scratching if necessary. If the yellowish orange hydrazone does not separate, the solution is heated in a got water bath for about 10 minutes. It is cooled, filtered at the pump, recrystallised from alcohol and melting point is determined. (b) Semicarbazones. About 0.25 g of asemicarbazide hydrochloride is added to 2.5 ml of water followed by 0.25g of anhydrous sodium acetate and warmed gently until a clear solution is obtained. A solution of 0.25 g of the substance in 1 ml of methanol is added and warmed on a water bath.It is cooled. Crystals of semicarbazone filtered and washed with water. It is recrystallised from alcohol, dried and the melting point determined. (c) Oximes. About 0.25 g of hydroxylamine hydrochloride is dissolved in about 2 ml of water. About 0.25 g of sodium acetate and 0.1g of the compound are added into it. In case the compound is water insoluble, sufficient amount of alcohol is added to the mixture to give a clear solution. The mixture is then heated on a water bath for about 15 minutes and then cooled in ice.Precipitation may be induced by adding a few drops of water. Filtered, washed with cold water, recrystallised from dilute alcohol or benzene, dried and melting point is determined.
Derivatives for Acids. The following derivatives can be prepared for carboxylic acids (a) s- benzylthiouronium salts (b) amides (c) anilides (d) bromo-derivatives (e) nitration and (f) acid anhydride. (a) s- Benzylthiouronium salts. Dissolved about 0.2g of the acid in the minimum amount of hot water, 5% aqueous sodium hydroxide solution is added until the solution is just alkaline to methyl orange.Then one drop of dilute hydrochloric acid is added. The sodium salt of the acid thus prepared is poured into a solution of 0.3g of s-benzylthiouronium chloride in 3ml of water.The mixture is stirred and cooled in ice bath.Crystals are filtered at the pump, recrystallised from ethanol containing 10% of water, dried and melting point determined.
(b) Amides. Amide derivatives can be easily prepared for benzoicacid, phthalic acid, cinnamic acid and salicylic acids. About 0.5g of the acid is mixed with an equal quantity of phosphorous pentachloride in a mortar. The mixture is ground well till the evolution of fumes ceased. Then added a few ml of concentrated ammonia.Stirred well and some water is added. The amide formed is filtered at the pump, washed with water and dried. It is recrystallised from dilute alcohol and melting point is determined. (c) Anilides. About 0.4g of pure aniline are taken in a dry test tube.The mixture is boiled under reflux for about an hour,cooled and poured in an excess of dilute hydrochloric acid. It is filtered at the pump, washed with water and dried.It is then recrystallised from dilute alcohol and melting point determined. (d) Bromo derivatives. Bromo derivatives can be easily prepared for cinnamic acid. About 0.25g of the acid is dissolved in boiling water. Excess of bromine water is added till brown colour persisted. Crystals formed are filtered, washed with water and dried. Melting point determined. (e) Nitration. Nitro derivatives can be easily prepared for benzoic acid, salicylic acid etc.1ml of nitrating mixture is prepared by mixing equal volumes of conc. nitric acid and conc.sulphuric acid. About 0.25 g of the acid is added into the nitrating mixture in small portions at time with shaking. It is then heated on a water bath for about 30 minutes. It is cooled and poured into water. It is filtered at the pump, washed with water and dried. The melting point is determined. (f) Acid anhydride. Anhydried can be prepared for ortho- carboxylic acid like phthalic acid. About 0.25 g phthalic acid taken in a dry china dish and covered by means of an inverted funnel.the stem of the funnel is closed by means of cotton wool. The china dish is gently heated. Phthalic anhydride is formed which gets collected at the cooler side of the funnel. After cooling the funnel is removed and the anhydride collected. The melting point of the anhydride is then determined. Derivatives for Esters. The important method used for the preparation of derivatives of esters is hydrolysis to the corresponding acid. (a) Hydrolysis. About 1 ml or 1 g of the ester is mixed with about 10 ml of 20% solution of sodium hydroxide in a R.B flask and boiled under reflux for about 45 minutes. It is then transferred to abeaker, cooled and acidified with conc. Hydrochloric acid. The acid precipitated is filtered at the pump. Washed with cold water and dried. Melting point is determined. Derivatives of Amines. The following derivatives may be prepared for primary and secondary amines.(a)acetyl derivatives (b)benzoyl derivative and (c)picrates.In the case of tertiary amines, picrates are commonly prepared. (a) Acetylation. Since acetyl derivatives of aliphatic amines are usually soluble in cold water,acetylation can be carried out in the case of aromatic amines like aniline ,toluidines,Nmethyl aniline etc.About 0.5 ml of the amine ,if liquid or 0.5g,if solid is taken in a small R B flask or boiling test tube fitted with a reflux condenser.About 2.5ml of acetic anhydride and acetic acid mixture (equal volumes) is added and refluxed gently for 15 minutes.It is then poured into water.The solid anilide separated is filtered at the pump,washed with water and dried.It is recrystallised from dilute alcohol and melting point is noted. (b) Benzoylation.Benzoyl derivative can be prepared for primary amines like aniline, toluidines and for secondary amines like N-methyl aniline.Details of benzoylation refer under preparation of derivatives for phenols. (c) Picrates.Picrate derivative can be prepared for primary,secondary(except diphenyl amine) and tertiary amines.The given amine and picric acid(equal amounts)are dissolved separately in
cold ethanol to get saturated solutions.The two solutions are mixed and poured into a watch glass.Coloured crystals of picrate separate.Melting point is determined. (d) p-Nitroso derivative. p-Nitroso derivative can be prepared for the tertiary amine,N,Ndimethylaniline.About 0.5 ml of N,N-dimethylaniline is dissolved in about 4ml of dilute hydrochloric acid.It is cooled in ice and the added about 2ml of 20%sodium nitrite solution in drops.It is kept in ice bath with stirring for 5 minutes.Then dilute sodium hydroxide solution is added.A green precipitate of p-nitrosodimethylaniline is obtained.It is filtered at the pump ,dried and melting point is determined. Derivatives for Nitro Compounds. The important derivatives for mononitro-compounds are: (a) The nitro group is reduced to primary amino group.The primary amine obtained by reduction, can be diazotized and coupled as explained under preparation of derivatives for phenols.If aromatic primary amine is obtained by reduction,it can be diazotized and coupled with β-naphthol in alkaline solution (b) Further nitration to get solid dinitro compounds (c) In the case polynitro compounds, they can be partially reduced to solid nitroanilines and hence partial reduction serves a method for the preparation of derivative for polynitro hydrocarbons. (a) Reduction of mono-nitro compounds. As already explained, mono- nitro compounds are reduced to the corresponding primary amino compounds and with the amino compound benzoylation and azodye formation conducte. (b) Nitration. Nitration of benzene to solid meta-dinitrobenzene can be easily carried out.1ml of conc.nitric acid and 1ml of conc.sulphuric acid are mixed together in a boiling test-tube.About 0.25ml of nitrobenzene is added with shaking. The mixture is heated in a boiling water bath for about 15 minutes.It is then poured into cold water. It is filtered at the pump,washed with water and dried.It is recrystallised from alcohol and melting point is noted. (c) Reduction of polynitro hydrocarbons to aminonitro hydrocarbons. This method is used for the preparation of derivative for meta-dinitrobenzene.About 0.5g of powdered sulphur is added to a solution of 1.5g of sodium sulphide in about 7ml of water. The mixture is boiled until a clear solution is obtained. About 1g of meta-dinitrobenzene is boiled with about 50ml of water in a beaker. To the boiling solution is added the sodium sulphide solution prepared above, in a thin stream with stirring.When the addition is over, the mixture is boiled for about 30 minutes more and filtered hot.The filtrate is cooled when meta-nitroaniline separates. It is filtered at the pump, washed with cold water and dried. It is then recrystallised from hot water, dried and melting point is determined. Note:(i)For nitrophenols,benzoylation does not proceed smoothly and hence nitrophenols are reduced to aminophenols and then benzoylation is conducted (methods of reduction and benzoylation already explained)to obtain dibenzoyl derivative.(ii) For nitroaniline, benzoyl derivatives can be prepared. Derivatives for Amides. For amides other than urea,hydrolysis can be effected for the preparation of derivative. If the original compound is an aromatic amide, alkaline hydrolysis followed by acidification with hydrochloric acid gives a solid organic acid with definite melting point.In the case of aliphatic amides, the acid obtained after hydrolysis will remain in solution. In such case, the cold solution, when carefully neutralized and treated with s-benzylthiouronium chloride, deposits the thiouronium salt. (a) Hydrolysis. About 1 g of aromatic amide is taken in a R.B flask fitted with a reflux condenser. About 10 ml of 10% sodium hydroxide solution is added. It is heated for about 30
minutes. It is cooled and acidified with conc. Hydrochloric acid. The precipitated acid is filtered at the pump, washed, recrystallised from hot water, dried and melting point determined. Derivatives for Urea (a) Urea nitrate. A concentrated solution of urea in about 1 ml of water is prepared. Then a few drops of conc. Nitric acid are added with shaking. White crystalline precipitate of urea nitrate separates. It is filtered at the pump, dried and melting point is determined. (b) Urea Oxalate. A concentrated solution of urea in about 1 ml of water is prepared. Then add a concentrated aqueous solution of oxalic acid in drop with shaking. White crystalline precipitate of urea oxalate separates. Filtered at the pump, dried and melting point is determined. Derivative for Thiourea. s- Benzyl thiouronium chloride. About 0.5 g powdered thiourea and 0.8 ml of benzyl chloride are added to one ml of 95% ethanol in a small R.B. flask or boiling test tube fitted with reflux condenser. The mixture is warmed on a water bath with gentle shaking until effervescence subside. Then the mixture is boiled under reflux for 30 minutes. The solution is cooled in ice bath when crystals of s-Benzylthiouronium chloride separate. Crystals are filtered at the pump, dried and melting point is determined. 11. Derivatives for Anilides. The following derivatives can hbe prepared: (a) Hydrolysis to the corresponding acid and amine (b) bromo derivative and nitration. (c) Nitration. (a) Hydrolysis. Anilides undergo hydrolysis very slowly by alkalies and hence acid hydrolysis is usually employed. A bout 0.5 g of anilide is mixed with 5 ml of 70% sulphuric acid in a R.B flask or boiling test- tube fitted with a reflux water condenser. The mixture is gently boiled for about 15 minutes. Then the solution is cooled and diluted with about 5 ml of water. By hydrolysis, acetanilide gives liquid acetic acid and liquid aniline. With the aniline obtained, solid derivatives can be prepared and their melting points determined.In the case of benzanilide, solid benzoic acid is obtained by hydrolysis. The solid is filtered, dried and melting point is determined. (b) Bromination. Little of the anilide is dissolved in acetic acid. Then bromine in acetic acid is added with shaking until brown colour remained. It is then poured into water. The precipitated p-bromo derivative is filtered at the pump, washed with water and dried. It is recrystallised from alcohol, dried and melting point determined. (c) Nitration. Anilides are nitrated by using 80% nitric acid at 00 c and then poured into ice cold water. Nitration leads to a mixture of o- nitroderivative and p-nitroderivative. Ortho- derivative is soluble in cold alcohol while para- derivative is insoluble. 12 Derivative for carbohydrates. Osazone. About 1 g of sugar is dissolved in 15 ml water and add 4 g of phenyl hydrazine hydrochloride, 4 g of sodium acetate and 1 ml glacial acetic acid. Heated for 15 minutes in a water bath. The osazone formed is filtered, washed with water and dried. It is then recrystallized from alcohol, dried and melting point is determined.
Multistep synthesis 1. Benzoic acid – m- nitrobenzoic acid - Methyl m-Nitrobenzoate Step1: Electrophilic Aromatic Substitution of Benzoic Acid to Produce m-Nitrobenzoic Acid Recall from your lecture class that a carboxylic acid would be a meta-director in an electrophilic aromatic substitution reaction. In practice, this nitration reaction can result in the production of quite a bit of the ortho product as well, unless the temperature is kept very cold throughout the reaction. All of the materials that will be used in the experiment are in proportion to the amount of benzoic acid that is being reacted. Not more than 3 g of PhCOOH is used, and record its mass carefully Overall Reaction: COOH
COOH
Con. HNO3 Con.H 2SO4 COLD
NO2
m-Nitrobenzoic acid
Benzoic acid Mechanism:
HNO3 +
NO2
2 H2SO4 COOH
+ HSO4
+ H3O
COOH
COOH
H2SO4 NO2 H
NO 2
NO2
HSO4 First, prepare a nitrating mixture (NM) by slowly adding con. H2SO4 to con. HNO3 while cooling it in a small Erlenmeyer flask in an ice/water/salt bath to 0oC or less. Make this NM in proportion to the amount of benzoic acid that will be reacting, although the benzoic acid will not be in this mixture. For each g of benzoic acid, use 1 mL of concentrated H2SO4 and 0.67 mL of concentrated HNO3 to prepare this NM. Keep it cold. Second, prepare the reaction mixture (RM) in a large Erlenmeyer flask; this container will maximize cooling during the reaction. Add concentrated H2SO4 to the Erlenmeyer and cool it to 00C or less. 2.5 mL of H2SO4 for each gram of benzoic acid is used. Add the benzoic acid
slowly to the H2SO4, keeping the temperature below 00C. During the course of this mixing and the reaction to follow, the RM should stay below 00C and never exceed 50C. When all of the benzoic acid has been added to the H2SO4, it will be rather paste-like. Now, double-check that the RM is colder than 00C and slowly add the COLD NM to the COLD RM, mixing carefully and keeping it cold. Use a short disposable pipette to transfer it and be sure that the rate of addition allows for efficient cooling; remember that the RM should stay below 0oC and never exceed 50C. Add the NM very slowly at first, but the rate can be speeded up as the reaction proceeds. Use the temperature as a guide. After all of the NM has been added, keep the mixture cold for another 10-15 minutes with occasional stirring. Finally, pour the mixture over ice/water slurry of about 150 g of ice and 200 mL of water. Stir vigorously and the product precipitates. Filter the product from the mixture, wash well with cold water, and allow it to dry. When the product is completely dry, obtains its mass and calculates the theoretical and percentage of yield for the reaction. Check its purity by mp, IR. The product is usually of sufficient purity to use for the next step, but if that is not the case, recrystallize it from hot water.
Step 2: Fischer Esterification of m-Nitrobenzoic Acid to Produce Methyl m-Nitrobenzoate Overall Reaction: COOH
+ NO2
m-Nitrobenzoic acid
CH3OH
COOCH 3
Con.H 2SO4 HEAT NO2
Methyl m-Nitrobenzoate
Mechanism: H H
O
O
O
O
O
C
S H
C O
O
O
H O H
O
O S
O
H
NO2
H
NO2 H
O
H
O
C O
O
C
H
O
C
H
O NO 2
NO 2
H
NO 2
H O
O
C O O NO 2
C
H
O
H NO 2
CH3
O
H O
H
H
C
O
O
H
H
transf er of proton
H
CH 3
NO2
CH3
H
O
O O
H
C O
H
C
CH 3
O
O S
O
H
O
O
NO 2 NO2
CH3
As in the previous step, the amounts of reagents used for this procedure will depend on the mass of m-nitrobenzoic acid that is used in the reaction. Use no more than 3 g of it. It is also critical that the m-nitrobenzoic acid is completely dry, since this reaction is an equilibrium process and water in a wet sample will drive the reaction in the reverse direction, reducing the yield of the product. For each gram of m-nitrobenzoic acid 8 mL of methanol is required and for each 20 mL of methanol, 1 mL of concentrated H2SO4is required. Consider the total volume of this mixture, and choose a round bottom flask that holds about twice that volume; in other words, choose a flask so that it is about half full. Put the three materials in the proportions described above into the round bottom flask with a couple of boiling chips, and attach a reflux condenser to form a reflux apparatus. Heat to reflux for 1 hour. Pour the reaction mixture into ice /water slurry (use a total volume of slurry of about 5 times the volume of methanol used) and stir. Once the ice is melted, use suction filtration to isolate the product and wash it with water. The crude product should be recrystallized from
methanol or methanol/water. Once it is completely dry, determine its mass and calculate its theoretical and percent yield. Also, determine its purity by mp and IR. Multi-Step Synthesis Yield Calculation. When you carry out a series of reaction steps, you usually want to know the efficiency of the whole process. To do so, you can use the percent yields for each step to compute the overall percent yield. This is easiest to explain with an example. Suppose you carried out four reactions in sequence with the percent yields given below. Step 1: 87.5%; Step 2: 91.2%; Step 3: 79.3%; and Step 4: 81.9% The overall percent yield is computed as shown, here. Overall Percent Yield: 0.875 x 0.912 x 0.793 x 0.819 x 100 = 51.8% overall. Be sure to compute the overall percent yield for the two steps of you synthesis of methyl mnitrobenzoate. 2. Aniline -acetanilide- p-bromoacetanilide- p-bromoaniline Step 1: Acetylation of Aniline In the first step we need to put the removable acetyl protecting group on the nitrogen of aniline. The acetyl group is electron withdrawing and it therefore makes the lone pair on the nitrogen less reactive either in an oxidation reaction or a protonation reaction. Bromination of aniline suffers from lack of control. The electron donating amino group activates the ring to such a great extent that usually tribromoaniline is isolated. However, if aniline is converted to acetanilide the monosustitution is easily achieved because the acetamino group cannot activate benzene ring towards electrophilic attack as well as simple amino group does. The acetamino group is less effective in donating electron density to the benzene ring, because the electron pair on the nitrogen atom is delocalized by both the carbonyl group and the phenyl ring. It should be kept in mind, however, that the acetamino group is still an activating group. 2. The acetic acid used in the brominating step causes protonation. Protonation of the nitrogen of aniline makes it a very strong deactivating group, making the aromatic ring less susceptible to reaction and would be a meta director. Another value of the acetyl protecting group is that it is bulky group and preferentially directs the bromination to the para position rather than the ortho position. The full mechanism for the reaction is givenbelow. Acetic anhydride ispartially protonated by the acetic acid. This makes the anhydride an even better electrophile for the nucleophilic nitrogen of aniline. This attacks to form the tetrahedral intermediate, which, after proton transfer, loses acetic acid. H 3C NH 2
H 3C
C
C O
O NHCOCH3
O
CH3COOH Procedure: Dissolve 4.0 mL of aniline in 10 mL of acetic acid in a 100 mL round bottom flask. To this solution, add 5 mL of acetic anhydride and mix well by swirling. CAUTION: the reaction is exothermic and the flask becomes warm. Add two boiling chips, attach a condensing column and attach the hoses for water cooling. Heat at a gentle reflux for fifteen minutes. After fifteen minutes, allow the flask to cool slightly. Cautiously add 5 mL of cold water through the top of the condenser into the reaction mixture. Boil the solution for an additional five minutes so as
to hydrolyze any unreacted acetic anhydride. After boiling for five minutes, allow the reaction mixture to cool slightly and then pour it slowly with stirring into 30 mL of ice cold water. After allowing the mixture to stand for 15 minutes with occasional stirring, collect the precipitate by suction filtration using your Buchner funnel. Be sure to wet the filter paper before you filter. Disconnect from the vacuum, wash the solid crystals with 10 mL of cold water and reconnect the vacuum tube for a couple of minutes more so as to dry the product as much as possible. Transfer the crystals to a watch glass and leave them to dry. Weigh the product and record the yield. Mechanism H O
O
C
C
CH 3
+ H
O
C
C
H 3C
O
O CH 3
H 3C
H 2N O
C
O
O
O O
C
CH3
O
H 3C
H O
H
H
C O C CH 3 H3C
H N H
O
O C H 3C
O
C
H
N
O
CH3 C
CH3 C
H
CH3
+
C
C O
O
O
O
C
CH 3
O
H3C
O
O
H O NHCOCH3
CH3
+
HO C
CH 3
O
Bromination of acetanilide NHCOCH 3
NHCOCH3
Br 2 Glacial acetic acid Br
Acetanilide the starting reagent in this synthesis is a mild analgesic and a mild antipyretic. The antipyretic properties of acetanilide was discovered by accident when a sample, improperly labeled and thought to be naphthalene was inadvertently administered to a patient in 1886.
H
H
and
N C
N
O
C
H 3C
O
H 3C
NH C
O
H 3C
Place 2.0g of acetanilide in 50mL Erlenmeyer flask. Add 7.5mL of glacial acetic acid and swirl the flask until the solid dissolves. Fill 1:4 (V/V) bromine/glacial acetic acid in a burette and clamp it on the stand. Add about 4.4 mL of the bromine acetic acid mixture drop by drop over a 10 minute period with stirring. Stir the reaction mixture for about 15 minutes to complete the reaction. Pour the reaction mixture into a 250mL beaker containing 60mL water. Rinse the flask with 15mL of water and add this rinse to the beaker. Stir the precipitated solid well with a stirring rod to break up any chunks. The solution is in orange colour due excess bromine. Destroy the excess bromine by adding small portion of sodium bisulphate. Collect the product by vacuum filtration and wash the residue four times with 15mL portions of water. Flow air through the residue for drying. Collect the solid, spread it on a watch glass to dry out. Once dried weigh the crude and recrystallize a small portion from dilute alcohol. Record the melting point, and IR spectrum. Alternative Green Procedure: NHCOCH3
NHCOCH 3
CAN, KBr H2O, EtOH Br
Chemicals Required: Acetanilide - 1 g Potassium bromide - 1 g Ceric ammonium nitrate - 6 g Ethanol - 15 mL Water - 15 mL In a 250 ml conical flask acetanilide (1 g) was dissolved in ethanol (15 ml). Then potassium bromide (1 g) and ceric ammonium nitrate (6 g) were dissolved in water (15 ml). This solution was transferred into an addition funnel. This solution was added drop wise to the conical flask containing acetanilide solution. After the addition was over, the reaction mixture was stirred for 10 minutes in room temperature (white crystals appeared). Then this solution was poured into ice-cold water. The white crystals were filtered through Buchner funnel and the solid was dried. Yield: 1.34 g (85 %) o
M.p. of p-bromoacetanilide = 165 C
Mechanism: Ce(IV)
+
Br
H2O
[Br ]
Ce(IV)
NHCOCH3
NHCOCH 3
[Br ] NHCOCH3
-H
[Br ]
Br
H
Br
Preparation of p-bromoaniline H 3C O Br
NH
+ (1) H /H2O Br
NH2
(2) OH
Transfer all of the crude p-bromoacetanilide that was prepared above to a 100 mL round bottom flask. Add 10 mL of water and 10 mL of concentrated hydrochloric acid. Add two boiling chips and reflux the mixture at a gentle boil for 15- 20 minutes using your heating mantle. Since we are not using a flammable organic solvent, it is also safe in this step to use a low flame with your Bunsen burner, using your tripod and wire gauze. As you heat, swirl the flask to ensure mixing and to dissolve any remaining solid. All of the solid will dissolve and the solution will become orange in color.After 20 minutes of reflux at a gentle boil, remove the heat source and add 15 mL of water. Cool the flask to room temperature. Crystals of p-bromoaniline may separate. Prepare a solution containing 10 mL concentrated aqueous 40 mL water and 25 g ice in a 400 mL beaker. Pour the solution of p-bromoaniline from above into this solution. Stir the suspension and test the pH of thesolution by placing a drop on the test strip. It must be strongly basic (blue to litmus). Ifnot, add more concentrated ammonia.Collect the orange precipitate of p-boromoaniline by suction filtration using Buchner funnel and wash the solid filter cake with 10 mL of cold water. Recrystallize the rest of the material from water. Take about 0.5 gram of your product and recrystallize it from approximately 15mL of water. Use your 50 mL Erlenmeyer. Put ~ 0.5 g in the Erlenmeyer and add 10 mLof water. Use your stirring rod to disperse the compound as much as possible in the water to aid in dissolution. Heat the suspension to boiling. (It is safe to use your Bunsen burner here since we are using water). Once the water is boiling, stir the solution add more water 1-2 mL at a time until all of the material has dissolved. Once the solution becomes clear, remove it from the heat and allow it to cool slowly to room temperature and then immerse it in an ice bath. Collect the crystals by suction filtration using your Hirsh funnel. Leave the crystals to dry; then determine the melting point. Record the weight and calculate the percent yield. Run a TLC of the crude and the recrystallized sample using dichloromethane as the solvent
Mechanism H3 C O Br
+
H
C NH
OH
C NH
Br
H 3C Br
OH Br
C NH
Br
OH
H
+
H3 C
H
O
H
NH 2
C NH
OH
OH
H 3C
H 3C
H
O
Br
H 3C
H 3C
NH
C Br
HSO4
NH
O H
OH
O
3. Synthesis of Dibenzalacetone by Aldol Condensation The reaction of an aldehyde with a ketone employing sodium hydroxide as the base is an example of a mixed aldol condensation reaction, the Claisen-Schmidt reaction. Dibenzalacetone is readily prepared by condensation of acetone with two equivalents of benzaldehyde. The aldehyde carbonyl is more reactive than that of the ketone and therefore reacts rapidly with the anion of the ketone to give a α-hydroxyketone, which easily undergoes base-catalyzed dehydration. Depending on the relative quantities of the reactants, the reaction can give either mono- or dibenzalacetone. O H
O O
+
Benzaldehyde
C H3 C
CH 3
Acetone
Dibenzalacetone 1,5-diphenyl-1,4-pentadiene-3-one Melting point 1100C, max 320nm, max=34,300
In the present experiment, sufficient ethanol is present as solvent to readily dissolve the starting material, benzaldehyde, and also the intermediate, benzalacetone. The benzalacetone, once formed, can then easily react with another mole of benzaldehyde to give the product, dibenzalacetone. Procedure: In a 125 mL Erlenmeyer flask, dissolve 0.020 moles sodium hydroxide (pellets) in 4.0 mL of water. In a 50 ml Erlenmeyer flask weigh out accurately 0.0160 moles benzaldehye andweigh into the same flask 0.0080 moles acetone. Add 10 ml of 95% ethanol and pourthis mixture into the prepared solution of sodium hydroxide. Mix and swirl occasionallyfor fifteen minutes. A yellow, flocculent precipitate should form. Filter the solid product by vacuum using your spatula to transfer as much of the solid as possible. After no more liquid is coming through the filter paper, disconnect the filter flask from the vacuum line, wash the solid with 10 mL water and, after about one minute, reconnect to the vacuum. Repeat the wash in the same way using 23 mL chilled 95% ethanol. Allow air to be sucked around the crystals for about 2 minutes. Recrystallize the product from ethyl acetate using a water bath and hot plate to heat the solvent. Ethyl acetate is flammable. Use approximately 2.5 mL of solvent per gram of product. Add about 1/2 the expected amount of ethyl acetate, stir with your spatula and heat thesuspension to boiling. Add more ethyl acetate in 1 mL portions, reheating to boiling each time, until all solid material dissolves (solution becomes clear). Allow the solution to cool slowly to room temperature and
then cool in an ice bath. Collect the final product on the Buchner funnel by suction filtration. Record the weight of your compound and calculate the percent yield. Take the melting point. Mechanism H H
O
C H3 C
CH2 H
O C
O
C
OH H3 C
CH2
H O
C
C
CH 2
H 3C H
H H
C
C
O
C
CH
CH 2 H2 C
H O
O
- H2O
CH
C
O
H O
O
H
HC
C
C
OH
+ OH
O
H
H O
H2 C
CH H
H O
C
C H 3C
OH
C
H O
OH
H
OH
HC
C
C
OH
HC
+ OH
C
C
-H2O
H
H
HC
HC
C
C
OH
C H
Acetone enolizes in the strongly basic conditions. Note that benzaldehye cannot enolize and so it must act as the electrophile. The nucleophilic alpha carbon then attacks the carbonyl of benzaldehyde. After proton transfer there is loss of water to give the a,b-unsaturated carbonyl that is stabilized by conjugation with the phenyl substituent. Notice how the π-electrons of the phenyl ring are delocalized all the way onto the carbonyl and onto the other carbonyl in the final dibenzylacetone product. 4. Preparation of Methyl Orange Methyl orange is synthesized from sulfanilic acid and N,N-dimethylaniline using a diazonium coupling reaction. The first step is called “diazotization.” Sodium sulfanilate reacts with sodium nitrite in hydrochloric acid (i.e., nitroso cation) to form an unstable “diazonium salt.” The second step is the “diazonium coupling reaction.” The diazonium ion is used in situ, and reacts with N, N-dimethylaniline to form the acidic azo dye.
SO-3
SO3H
SO3- +Na
+
2
Na 2CO3
NH+3
NH2
+
2
CO2
+
H2 O
NH2 Sodium Sulfanilate
Sulfanilic Acid (zwitterion)
SO 3- +Na
SO 3- +Na HCl / NO2-
Sodium Sulfanilate Diazonium Chloride
N N+ Cl-
NH2 SO 3- +Na + N N
+ Cl-
CH3 H3C
N
CH 3COOH
Na O3S
N
CH3
N
N CH3
Methylorange
N,N-Dimethylaniline
Methyl orange forms beautiful orange crystals and is used as an acid-base indicator The anion form is yellow and the acid form is red. O
X O S
CH 3 N
N
N
HO CH3
O H
Yellow p > 4.4
O
H
CH 3
S
N
N
N CH 3
O
Red
pH<
3.1 Inner salt f orm
Mechanism The first step is simply an acid base reaction. In order to dissolve the sulfanilic acid in the aqueous solution we add sodium carbonate.. When we add sodium nitrite and HCl, the nitroso ion is formed from sodium nitrite and this reacts with the amine to form a nitrosoammonium adduct that loses water under the acidic conditions after proton transfer. This gives the diazonium salt. Aromatic diazonium salts are stable at low temperature. The terminal nitrogen of the diazonium salt is very electron deficient. It can be attacked by good nucleophiles. We dissolve the dimethylaniline in acetic acid. This forms the dimethylaniline acetate salt. Neutralize this in situ and the dimethylaniline becomes a good nucleophile due to the activating effect of the dimethylamine substituent. Attack is in the para position due to hindrance at the ortho position by the bulky dimethylamine substituent.
O
O
N +
HCl
H
O
H2O +
O
O
HO
O
Na O
H
H
H2O
O Na O S
NH 2
HO
O
O
N
S
NH 2
O HO
HCl
O
O HO
N
O
N
Na O C
N
HCl
O
H
S
N
O
H
H
Cl
N
O
N
O
O
S
N
N
O
O
H
HO
S
N
O
H
H2O
H
H
H
Cl
CH 3
O
O HO
S
N
N
Cl
H3C
C
O
OH
N H3C H
O HO
S
N
N
N
O CH 3
O
H 3C
CH 3
CH3 N
H
O HO
S O
CH 3 N
N
N CH3
Procedure: In order to avoid any excess of a reagent that could decompose or cause decomposition and produce tar to contaminate our dye, you need to weigh the quantities of solid reagent very carefully to the accuracy of 0.05 g or better. In this experiment you will have to calculate for yourself some of the amounts of needed reagents. After you have calculated them, confirm your results with the instructor before proceeding. Dissolve 0.010 mole of sulfanilic acid (anhydride) in about 50 ml of a solution of sodium carbonate containing 0.010 to 0.0125 moles of sodium carbonate in a 125 ml Erlenmeyer flask. The solution is prepared by the stockroom and its strength is indicated on the bottle, but you must calculate the exact amount needed. Warm the mixture slightly to speed up dissolution. Test one drop of the solution to make sure it is alkaline. If not, add a small amount (1-2 mL) sodium carbonate solution and check the pH again. Then add 0.010 moles sodium nitrite and cool to 25°C (room temperature). Put 40 g of ice in a 400 mL beaker and add enough hydrochloric acid of a 6M or a 12 M solution in order to provide a total of 0.030 mol HCl in the beaker. Add the
sulfanilate solution prepared above in a fine stream while stirring continuously. Keep this solution cold in the ice bath at all times. It now contains your diazonium salt, which will decompose if it becomes warm. It is only partially soluble in the aqueous solution and will precipitate as a bluish-greenish solid. Prepare a solution of N,N-dimethylaniline (0.010 mol) in 0.010 mol of acetic acid in a 25 ml Erlenmeyer flask. Now add the dimethylaniline acetate solution slowly with constant stirring to the suspension of the diazonium salt. A dull, reddish-purple mass should appear. Now, very slowly add about 30 mL of 1.0 M sodium hydroxide solution with constant stirring. Add the NaOH a few mL at a time. The addition should take 10 -15 minutes. The actual coupling reaction does not occur until you add the NaOH. The reaction takes place best at about pH 7. Keep adding the NaOH until the solution becomes basic (blue to litmus). If the sodium hydroxide is added too quickly, then free dimethylaniline will separate out as an oily phase. This then leaves an equivalent amount of the diazonium salt unreacted. This excess salt decomposes to brown tar on warming to room temperature and contaminates the otherwise beautiful crystalline orange dye. At the end of the coupling reaction a yellow-orange or golden color should be observed. The product will now be recrystallized from the reaction mixture. Heat the reaction mixture to boiling using your tripod and Bunsen burner. Everything should dissolve and the solution should be clear (though it will be highly colored). If all the material does not dissolve when the solution is heated to boiling, add more water as needed. Then, allow it to cool slowly to room temperature to crystallize and then place the flask in an ice bath to get it as cold as possible. Remember: do not stir or shake the solution when it is cooling. Allow the crystals to form in an undisturbed flask. They will be much purer and larger if they form slowly in a motionless flask.
ORGANIC ESTIMATIONS 1. ESTIMATION OF ANILINE/PHENOL. The reaction to be studied in this experiment is between bromate and bromide ions in the presence of acid and occurs according to the equation, KBrO3 + 5KBr + 3H2SO4 3K2SO4 + 3H2O + 3Br2 In this reaction, the potassium and sulphate ions are “spectator” ions in that they are not themselves materially affected, so, in ionic terms the reaction may be summarised as, 5Br + BrO - + 6H+ + 3Br + 3H O 3
2
2
The free bromine generated reacts with phenol /aniline forming tribromophenol/aniline. OH
OH Br
+
Br
+
3Br 2
3HBr
Br
Equivalent mass of phenol/aniline
= = 15.5 (aniline) A bromate-bromide mixture which easily liberate bromine in presence of an acid is used so as keep the concentration of bromine a constant. Requirments: 1. Approximately N/10sodium thiosulphate. 2. Approximately N/10 brominating mixture.
3. 10% potassium iodide solution. 4. starch solution. Procedure: (a) standardisation of sodium thiosulphate solution. About 1.25 g of A.R. potassium dichromate is weighed out into a 250 ml standard flask. It is dissolved in water and made up to the mark. 20 ml of the made up solution is pippeted out into a conical flask. About 3 ml of conc. HCl is added ,followed by 5 ml of 10% KI solution. It is titrated against sodium thiosulphate solution using starch as the indicator. Titration is repeated till concordant results are obtained. (b)Estimation of aniline/phenol. The given aniline solution is made up to 100 ml. 20 ml of aniline and 40 ml of brominating mixture are pippeted out into a stoppered conical flask and diluted with 25 ml of water. 5ml of conc. HCl is added, and the flask is shaken for a minute to mix the reactants. It is allowed to stand for 30 minutes with occasional shaking of the contents of the flask. Flask is cooled under tap and 20 ml of 10% KI solution is added in the cup around the stopper. The stopper is dislodged whereupon the iodide solution is drawn into the flask with no loss of bromine. The flask is shaken for 30 seconds and allowed to stand for 10 minutes.the stopper is removed and the neck of the flask and stopper are washed with a little water. The free iodine is titrated against sodium thiosulphate using starch as the indicator. The volume of thiosulphate will be equivalent to the excess of bromine. A blank analysis is carried out using 20 ml of brominating mixture and 20 ml of water, the procedure being otherwise identical with the analysis of aniline. Calculation: Let the strength of sodium thiosulphate be Let 20 ml of brominating mixture Amount of brominating mixture used in the estimation 40 ml of brominating mixture 20 ml of aniline solution+40 ml of brominating mixture after the reaction
= N1 = V ml of Na2S2O3 = 40 ml = 2V ml of Na2S2O3 = V2 ml of Na2S2O3
Amount of sodium thiosulphate equivalent to aniline Normality of Aniline
= (2V-V2) ml =
Result: Mass of aniline in the whole of the given solution
= ………….. g
2. Estimation of Ester Principle: Ester is hydrolyzed quantitatively with known volume of standard alkali. The unreacted alkali is then titrated against standard acid. The amount of reacted alkali can be found out. From this, the amount of ester can be calculated. CH3-COOC2H5 + NaOH CH3COONa+ C2H5OH Procedure: About 1 g of given ester is weighed out into a 250 ml round-bottomed flask. 50 ml of standard N/2 sodium hydroxide solution is added a reflux condenser is fitted into the flask. The contents into the flask are refluxed on a stand bath for 2 hours. The completion of hydrolysis is indicated
by the disappearance of pleasant smell of ester. The contents of the flask are quantitatively transferred into 250 ml standard flask and made up to mark. 25 ml of the solution is titrated against N/2 HCl. From the titre value, percentage of ester in the given sample is calculated. Calculation: Weight of ester =Wg Normality of NaOH = N1 Normality of HCl = N2 50x N1 = Volume of 1 N NaOH Volume of HCl Unreacted NaOH = V2 ml V2x N2 = Volume of unreacted NaOH x Normality of NaOH Volume of unreacted NaOH
=
= V3ml
V3XN1 = Volume of 1 N NaOH Volume of 1N NaOH unreacted NaOH = V3XN1 = V4 Volume of 1N NaOH that has reacted =V1-V4 1000 ml 1 N NaOH 1000 ml 1N ester = 88 g of ester (where 88 is the molecular weight of CH3-COOC2H5) 1 ml 1 N NaOH
=
(V1-V4) ml 1 N NaOH
=
Percentage composition of ester
=
Result: The percentage composition of the ester
=…………g
g of ester
= W1 g
3. Estimation of iodine value of an ester The iodine value is expressed in grams of iodine for the amount of halogens linked with 100g test sample, and is used as degree of unsaturated bond of fats and oils. Iodine value is a measure of the total number of double bonds present in fats and oils. It is expressed as the «number of grams of iodine that will react with the double bonds in 100 grams of fats or oils». The determination is conducted by dissolving a weighed sample in a non-polar solvent such as cyclohexane, then adding glacial acetic acid. The double bonds are reacted with an excess of a solution of iodine monochloride in glacial acetic acid (“Wijs’ solution”). Mercuric ions are added to hasten the reaction. After completion of the reaction, the excess iodine monochloride is decomposed to iodine by the addition of aqueous potassium iodide solution, which is then titrated with standard sodium thiosulfate solution. Principle: A solution of a definite mass of oil in a suitable solvent such as carbon tetrachloride is treated with a known excess of iodine monochloride in glacial acetic acid (Wij’s solution). The excess iodine monochloride is treated with excess of potassium iodide and the liberated iodine is estimated by titration with standard thiosulphate solution. From the results the iodine value is calculated. Requirements: 1.Wij’s solution(Iodine monochloride) 2. Standard sodium thiosulphate solution N/10 3. Approximately 10% solution of potassium iodide.
4. Carbon tetrachloride. 5. Freshly prepared 1% starch solution. Procedure: (a) Preparation of wij’s solution: About 6.5 g of pure finely powdered iodine is accurately weighed and dissolved in 500 ml of pure glacial acetic acid contained in a round bottim flask. The flask is warmed to facilitate the dissolution of iodine. When cooled, 50 ml of the solution is transferred into another flask and pure dry chlorine is passed through it till the colour changes from dark brown to clear orange. The remaining iodine solution is then added, when the colour of the solution turns to light brown. The solution is next heated on a water bath for 20 minutes. ICl
+
KI
I2
ICl
2I
+
KI
(b)Estimation: About 0.2 g of oil is weighed out into a clean dry stoppered bottle of 500 ml capacity. It is then dissolved in about i0 ml of carbon tetrachloride. 25 ml of iodine monochloride solution is then run in from a burette. The resulting mixture, if turbid, is cleared by adding more carbon tetrachloride. The bottle is gently rotated to mix the contents thoroughly. The bottle is then kept aside for about half an hour. Then 20 ml of 10% KI solution are added and the mixture diluted by adding 200 ml of water. The mixture is then titrated with standard thiosulphate solution using starch as indictor. A blank determination is carried out without the oil using exactly the same quantity of carbon tetrachloride and the same pipette for delivering the wij’s solution. Calculation If V1 ml of thiosulphate is required for the blank and V2 ml for reacting with the excess of iodine monochloride in the actual experiment, Then the iodine value. S = The strength of thiosulphate W = Mass of oil taken Result: Iodine value of the given oil
= ……….g
4. Estimation of saponification value of an oil or fat Fats and oils are the principle stored forms of energy in many organisms. They are highly reduced compounds and are derivatives of fatty acids. Fatty acids are carboxylic acids with hydrocarbon chains of 4 to 36 carbons; they can be saturated or unsaturated. The simplest lipids constructed from fatty acids are triacylglycerols or triglycerides. Triacylglycerols are composed of three fatty acids each in ester linkage with a single glycerol. Since the polar hydroxyls of glycerol and the polar carboxylates of the fatty acids are bound in ester linkages, triacyl glycerols are non polar, hydrophobic molecules, which are insoluble in water. Saponification is the hydrolysis of fats or oils under basic conditions to afford glycerol and the salt of the corresponding fatty acid.
It is important to the industrial user to know the amount of free fatty acid present, since this determines in large measure the refining loss. The amount of free fatty acid is estimated by determining the quantity of alkali that must be added to the fat to render it neutral. This is done by warming a known amount of the fat with strong aqueous caustic soda solution, which converts the free fatty acid into soap. This soap is then removed and the amount of fat remaining is then determined. The loss is estimated by subtracting this amount from the amount of fat originally taken for the test. The saponification number is the number of milligrams of potassium hydroxide required to neutralize the fatty acids resulting from the complete hydrolysis of 1g of fat. It gives information concerning the character of the fatty acids of the fat- the longer the carbon chain; the less acid is liberated per gram of fat hydrolysed. It is also considered as a measure of the average molecular weight (or chain length) of all the fatty acids present. The long chain fatty acids found in fats have low saponification value because they have a relatively fewer number of carboxylic functional groups per unit mass of the fat and therefore high molecular weight. Requirements: 1. N/2Alcoholic potash. 2. N/2 Hydrochloric acid Procedure: About 1 to 2 g of ester (oil or fat) is weighed out accurately into a round bottomed flask. The flask is fitted with reflux condenser. 25ml of N/2 alcoholic potash are added and the flask is heated on water bath for about one hour. When reaction is completed, the liquid becomes clear. A blank experiment is performed simultaneously with the same quantity of alcoholic potash. Both flasks are cooled and the alkali in both is estimated by titration with N/2 hydrocholric acid using phenolphthalein as indicator. From the results the saponification value is calculated Calculation Let V1 and V2 be volumes of standard acid required for the estimation and the blank and W be the mass of ester/oil taken Then the alkali used up by the ester = (V2-V1) ml 1 ml of Normal alkali = 56.1 mg of KOH Hence saponification value Result Saponification value of the given ester
= = …………..g
5. ESTIMATION OF GLUCOSE Glucose is a very important monosaccharide in biology. It is one of the major products of photosynthesis. The living cell uses it as a source of energy and metabolic intermediate. The name comes from the Greek word glykys, which means "sweet", plus the suffix "-ose" which denotes a sugar. Two stereoisomers of the aldohexose sugars are known as glucose, only one of which (D-glucose) is biologically active. This form (D-glucose) is often referred to as dextrose monohydrate, or, especially in the food industry, simply dextrose (from dextrorotatory glucose). Fehling's solution is always prepared fresh in the laboratory. It is made initially as two separate solutions, known as Fehling's A and Fehling's B. Fehling's A is a blue aqueous solution of copper (II) sulfate pentahydrate crystals, while Fehling's B is a clear solution of aqueous potassium sodium tartrate (also known as Rochelle salt) and a strong alkali (commonly sodium hydroxide).Equal volumes of the two mixtures are mixed together to get the final Fehling's solution, which is a deep blue colour. In this final mixture, aqueous tartrate ions from the dissolved Rochelle salt chelate to Cu2+ (aq) ions from the dissolved copper sulphate crystals, as bidentate ligands giving the bistartratocuprate(II) complex as shown below.
Methylene Blue: Methylene blue is a heterocyclic aromatic chemical compound with the molecular formula C16H18N3SCl. It has many uses in a range of different fields, such as biology and chemistry. At room temperature it appears as a solid, odorless, dark green powder, which yields a blue solution when dissolved in water. The hydrated form has 3 molecules of water per molecule of methylene blue. Methylene blue should not be confused with methyl blue, another histology stain, new methylene blue, or with the methyl violets often used as pH indicators. The International Nonproprietary Name (INN) of methylene blue is methylthioninium chloride.
Methylene blue is widely used as redox indicator in analytical chemistry. Solutions of this substance are blue when in an oxidizing environment, but will turn colorless if exposed to a reducing agent. The redox properties can be seen in a classical demonstration of chemical kinetics in general chemistry, the "blue bottle" experiment. Typically, a solution is made of dextrose, methylene blue, and sodium hydroxide. Upon shaking the bottle, oxygen oxidizes methylene blue, and the solution turns blue. The dextrose will gradually reduce the methylene blue to its colorless, reduced form. Hence, when the dissolved oxygen is entirely consumed, the solution will turn colorless. Theory of Estimation of Glucose: A freshly prepared Fehling’s solution is first standardized by titration against a standard solution of pure glucose A.R. The standardized Fehling’s solution is then used to determine the amount of glucose in an unknown sample or solution by direct titration. The Fehling’s solution being a solution of cupric ions is blue in colour and at the end point changes to red colour precipitate of cuprous oxide. As the supernatant liquid is blue and the precipitate is red in colour, there may be some difficulty in determination of end point accurately. Hence sometimes a methylene-blue indicator is employed for accurate determination of the end point. C6H12O6 + 2CuO → C6H11O5.COOH + Cu2O Glucose CupricOxide Gluconic Acid Cuprous oxide (Fehling’s solution)
Procedure: (a) Standardisation of fehlings solution. About 1.25 g of glucose is accurately weighed out into a 250 ml standard flask. It is dissolved in water and made up to 250 ml. 20 ml of freshly prepared fehling solution (10 ml each of I and II) is pipette out into a conical flask. It is diluted with equal volume water and boiled. To the boiling solution standard solution of glucose is added from the buretteuntill the blue colour just disappeared. This gives an approximate value of volume of the glucose required. The exact value is obtained by repeating the titration by adding so much of glucose solution that 0.5 ml to 1 ml will be required to complete the titration to another sample of fehling solution , the solution is kept boiling 3 to 5 drops of 1% aq.solution of methylene blue is added to it give a blue colour. The titration is completed within a minute. The end point will be the disappearance of blue colour with red ppt of Cu2O. The titration is repeated to get concordant values. (b)Estimation of glucose: Make up the given solution to 250 ml. pipette out 20 ml of the Fehling solution to a 250 ml conical flask diluted with an equal volume of water, heat to boiling add glucose solution, from a burette until the blue colour just disappears. This gives the approximate value of the glucose solution required. To obtain the exact value, repeat the titration and add so much of the glucose solution. So that 0.5 to 1 ml more is required to complete the reduction. Heat the solution to boiling for 2 minutes. Then without the removal of the flame
beneath the flask add 3-5 drops of 1% aq methylene blue indicator. Complete the titration in 1 minute by adding glucose solution drop wise until the colour of methylene blue just disappears. Repeat the experiment till the concordant value (+ 0.1 ml) is obtained. Calculation: Weight of glucose in 250 mL = W 1g Weight of glucose /mL of the solution = g 20mL of Fehling solution V1mL of glucose (standard) solution Weight of glucose/ mL of Fehling solution g 20 mL of the Fehling solution = V2 mL of glucose (estimation) solution Weight of glucose in the whole of given solution = g
Result: Weight of glucose in the whole of the given solution = ……………g
