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 Preliminary tests 1. Colour and appearance of the substance are noted
Observation (a) Colourless (b) Yellow
2. Odour is noted
3. Solubility is noted A little of the given compound is shaken with the following solvents (a) Cold water
(c) Brown or black (a) Pleasant fruity (b) Fishy or ammoniacal (c) Kerosene like smell (d) Bitter almond smell (e) Pungent (f) Carbolic
soluble
Insoluble
(b) Sodium hydroxide
(c) Dil.Hydrochloric acid
Soluble in sodium hydroxide and reappears as turbidity on adding excess of dil. HCl. Soluble and reappears as turbidity on adding excess of NaOH solution
Inference Presence of hydrocarbon, aldehydes, ketones ,acids esters etc. Presence of aromatic nitrocompounds Presence of phenol or amine Presence of ester Presence of amines Presence of hydrocarbon Presence of benzaldehyde of nitrobenzene Presence of halogen compounds Presence of phenol
Presence of sugars, lower aliphatic alcohols, aldehydes, ketones and esters. Presence of aromatic hydrocarbons, amines, phenols, higher aldehydes, ketones and esters.
Presence of acids or phenols.
Presence of amines
metallic sodium is melted melted in an ignition II. Detection of Elements. Lassaigne’s Test . A small piece of metallic 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
3.
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
To the third portion of the extract a few drops of freshly prepared sodium nitroprusside solution is added
A blue or green colouration or precipitate is obtained (a) White curdy precipitate soluble in ammonia (b) Yellowish white precipitate sparingly soluble in ammonia (c) yellow precipitate insoluble in ammonia
Nitrogen is present
Chlorine is present Bromine is present
Violet colouration
Sulphur is present.
Iodine is present.
III DETECTION OF CHARACTERISTIC GROUPS
1
2
Test to find whether aliphatic or aromatic (i)Ignition test. A small quantity of the (a) Burnt with a non-smoky substance is ignited on nickel spatula flame (b) Burnt with a smoky luminous flame (ii) Nitration test: A little of the substance is added to a mixture containing 2mL con. Sulphuric acid and 1mL con. Nitric acid taken in test tube. It is then heated on a boiling water Colourless solution bath for about half an hour and then poured into cold water taken in t he Yellow solution or precipitate beaker
Test to find out whether unsaturated or saturated (i) Action of dilute potassium permanganate: A little of the substance is shaken with water and one o r two (a) Immediate decolourisation drops of dil. potassium permanganate (b) Slow decolourisation solution
Presence of aliphatic substance Presence of aromatic substance
Presence of alphatic substance Presence of aromatic substance.
Presence of unsaturated compound Presence of easily oxidizable substance like phenol, niro phenol,
(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
Action of con. Sulphuric acid: A little of the substance is warmed with con.H2SO4
(1) Action of sodium hydroxide solution: A little of the substance is boiled with dilute sodium hydroxide solution
Decolourisation without the formation of a precipitate. No decolurisation (a) Decolourisation without the evolution of hydrogenbromide (b)Decolourisation with the evolution of hydrogen bromide (c) Decolourisation with formation of a precipitate.
(a) Charring with effervescence due to the liberation of sulphurdioxide, carbondioxide, carbonmonoxide and smell of burnt sugar (b) dissolves gradually on heating (c) White precipitate which dissolved in excess of acid (a) Ammonia is evolved (b) substance dissolved
(c)Separation of oil or formation of an emulsion (d)Solution turns deep yellow in colour
5
6
7
(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 t ube 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
amines, belnzaldehyde, etc. Presence ofunsaturated compound. Presence of saturated compound. Presence of unsaturated substance Presence of saturated substances Presence of easily brominated compounds like phenols, aromatic amines etc.
Presence of carbohydrate Presence of aromatic hydrocarbon Presence of basic substance like aromatic amines Presence of amide Presence of acidic substances like acids phenols and their derivatives Presence of anilides Presence of nitrophenols
Presence of aromatic esters and amides
(a) Ammonia gas is evolved (b) Kerosene lie smell
Brisk effervescence of carbondioxide
Presence of amides and amines Presence of acids
Presence of acids
8
9
10
11
12
13
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 Action of Schiff’s reagent: A little of the substance is added to 1mL Sc hiff’s reagent taken in test tube and shaken well 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
Brisk effervescence (a) Violet colour (b) A flocculent white precipitate (c) green colour changing to a white precipitate (d) Buff coloured precipitate
A yellowish orange precipitate is obtained
Violet colour developed within two minutes (a) Black or brown precipitate (b) Bright silver mirror is formed
Action of Fehling’s solution: Fehling’s solution A and Fehling’s solution B are mixed in equal volumes. To 1 mL of t his reagent a little of the organic Reddish brown precipitate is compound is added and heated on a formed boling water bath Action of Molish’s reagent: To a solution of substance in water added a few drops of alcoholic solution of α-naphthol. Then added about 1mL of con.H2SO4 along the sides of the test Violet ring is formed at the tube without disturbing junction
Presence of alcohols, acids and phenols. Presence of phenol Presence of α-naphthol Presence of β-naphthol Presence of benzoic acid, cinnamic acid or phthalic acid
Presence of aldehydes or ketones
Presence of aldehydes Presence of polyhydric phenol Presence of aldehydes, reducing sugars such glucose, fructose, maltose etc.
Presence of aldehydes, polyhydric phenols, and reducing sugars.
Presence of Carbohydrates.
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
Action of sodium hydroxide solution. A little of the substance heated with sodium hydroxide
(a) Ammonia is evolved (b)Separation of oil and formation of an emulsion
Presence of amides Presence of anilides
2
3
4
5
6
7
8
Action of Soda-lime: A little of the organic substance is heated with excess of dry soda-lime
(a) Ammonia is evolved
Biuret test:A little of the substance is gently heated in a dry test-tube 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 the substance is dissolved in dilute hydrochloric acid, cooled in ice water and a 10%solution of sodium nitrite is added with shaking till it is slightly in excess. With the solution obtained above the following tests are done. (i)To one portion of the solution an alkaline solution of β-naphthol is added. (ii)A portion of the solution is extracted with ether. The ether 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 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
A violet colour is produced.
Presence of diamide like urea.
(a) Liberation of nitrogen with the formation of alcohol. (b) Separation of an yellow oil. (c) Reddish brown solution is obtained.
Presence of aliphatic primary amines. Presence of secondary amines Presence of tertiary amines
A scarlet red precipitate is formed.
Presence of aromatic primary amines.
Blue or green solution is obtained.
Presence of secondary amines.
Ether layer becomes deep green.
Presence of tertiary amines.
Offensive smell is produced
Presence of primary amine
(b) Amine is roduced
Bright silver mirror or black precipitate is obtained.
Presence of amides and amines Presence of aminoacids, toluidines and anilides
Presence of nito group.
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 βnaphthol solution is added
An offensive smell is produced
Presence of nitro group
A scarlet precipitate is obtained
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 substance is shaken with hot water and tested with litmus
(a) soluble and acidic to litmus (b) Insoluble and acidic
(c) Insoluble and neutral
2
3
Action with silver nitrate solution. A little of the substance is boiled with sodium hydroxide solution for 15 minutes. Cooled, acidified with dil. nitric acid and then added silver 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.
(a) Precipitate of silver halide is formed (b) No precipitate of silver halide (a) Precipitate of silver halide is obtained (b) No precipitate of silver halide
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 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
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.
Ammonia is evolved
Presence of thiourea or sulphonamide
Pungent smell
Presence of substituted thiourea.
3
Fusion with alkali. A little of the substance is fused with sodium hydroxide dissolved in water anf hydrochloric acid is added
(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 sulphate Presence of amino when barium chloride is added sulphonic acid (d) Ammonia is evolved during fusion. No phenol is formed. Sulhur dioxide is evolved on Presence od adding acid sulphonamide D. If nitrogen, halogens and sulphur are absent, tests for the following groups for which indications are got, are done. I.Aldehydes
1. 2
Schiff’s reagent test is conducted Borsche’s reagent test is conducted. Note: Ketones also answer this test.
3
Tollen’s reagent test is conducted. Note: Other reducing reagents also answer this test.
4
Fehlling’s solution test is conducted.
Violet colour is obtained An yellow precipitate is obtained. Bright mirror or black precipitate is obtained.
Presence of aldehydes. Presence of aldehydes.
Red precipitate is obtained.
Presence of aldehydes.
White crystalline precipitate is obtained.
Presence of aldehydes.
White crystalline precipitate is obtained.
Presence of aldehydes.
Presence of aldehydes.
Note: Other reducing reagents also answer this test
5
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.
6
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.
II. Ketones.
1
Borsche’s reagent test is conducted.
An yellow precipitate is obtained .
Presence of ketones.
2
Semicarbazide test is conducted.
White crystalline precipitate is obtained
Presence of ketones.
3
Sodium bisulphate test is conducted.
White crystalline precipitate
Presence of ketones
4
Iodoform test is conducted
Yellow precipitate with characteristic odour is formed
Presence of ketones containing the CH 3-COgroup
Effervescence
Presence of acids.
Kerosene smell obtained Pleasant fruity smell.
Presence of acids.
White crystalline precipitate.
Presence of acids
A reddish solution having an intense green fluorescence is produced.
Presence of dicarboxylic acids.
III.Acids
1 2
Tested with sodium bicarbonate solution. Sodalime test is conducted
3
Ester formation test is conducted.
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 s-Benzylthiouronium 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.
IV.Phenols 1
2
3
4
5
Neutral ferric chloride solution test is conducted. A little of the substance is treated with neutral ferric chloride solution.
Liebermann’s nitroso reaction : To two drops of melted phenol, added little solid NaNO2 . Heated gently for 1 minute.Cooled and added 4 drops of conc.H2SO4. Diluted cautiously with water. Phthalein fusion reaction: About 2 drops of melted phenol is mixed with a small quantity of phthalic anhydride in a dry test-tube. 2 drops of conc.H2SO4 are added. The o mixture is heated at about 150 C for 2 min.Cooled and exess of 10 % 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 NaNO 2 solution are added. The diazonium solution thus obtained is added to a well cooled solution of phenol in aqueous NaOH solution.
(a) Violet blue or green colour. (b) Aflocculent white precipitate.
Presence of phenol.
Red solution which turned to green or blue on adding sodium hydroxide solution.
Presence of phenol.
Red, bluish-purple, blur green fluorescene, green or very faint green colouration.
Presence of phenol.
Crystalline white precipitate.
Presence of phenol.
Orange, scarlet,dark red, brownish red solution or precipitate is obtained.
Presence of phenol.
Presence ofαnaphthol.
V. Alcohols.
1 2
Test with metallic sodium is conducted. Acetylation test: A little of the substance is heated with glacial acetic acid and few
Brisk effervescence. Pleasant fruity smell is produced.
Presence of alcohols. Presence of alcohol.
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 formed.
Presence of ester.
A violet or a deep redbrown colour developed immediately
Presence of ester
VII Carbohydrates.
1
3
Concentrated sulphuric acid test is conducted. Warmed a little of the substance with conc. Sulphuric acid. 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:
2
6
Charring with smell of burnt sugar
Presence of carbohydrate.
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
Odour is noted.
2
Sulphonation is conducted : To 1 ml of
Kerosene like smell observed.
Presence of hydrocarbons.
3
4
5
fuming H2SO4 contained ina test tube, 2 drops of the substance are added and shaken well for 3 min. Nitration is conducted .
Substance has gone into solution.
Note.(1) To nitrate naphthalene, about 0.5g of naphthalene is dissolved in 2 ml of glacial acetic acid by gently warming, 0 cooled and heated to 80 c after adding conc. Nitric acid. It is then poured into water when yellow crystals separate. Picrate test is conducted : Saturated Red or yellow solutions of naphthalene and picric acid, precipitate. both in benzene are prepared separately. These two solutions are mixed in a watch glass and allowed to evaporate.
Presence of hydrocarbon.
Presence of polynuclear hydrocarbons.
Confirmation by preparing a solid derivative.
The final step in the analysis of a sample organic compound is the preparation of a suitable solid derivative.
Preparation of Derivatives
1.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. (b) 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. 4. 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- dinitro-phenyl 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. (b) 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. (c) 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. (d) 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
(b)
(c)
(d)
(e)
(f)
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. 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. 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. 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. 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. 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. 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. 8. 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,N-methyl 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,N-dimethylaniline.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 pnitrosodimethylaniline is obtained.It is filtered at the pump ,dried and melting point is determined. 9. Derivatives for Nitro Compounds . The important derivatives for mononitrocompounds are: (a) The nitro group is re duced 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 metanitroaniline 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. 10.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 sbenzylthiouronium chloride, deposits the thiouronium salt.
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 added 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. 0 (c) Nitration. Anilides are nitrated by using 80% nitric acid at 0 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 recrystallised from alcohol, dried and melting point is determined.
Multistep synthesis:
Nitrobenzene -Aniline -acetanilide-p-bromoacetanilide-p-bromoaniline Nirtobenzene-m-dinitrobenzene-m-nitro aniline (using Na2S +S) 1. Preparation of m- dinitrobenzene from nitrobenzene Place 21mL of con. Sulphuric acid and 15 ml of con nitric acid in a 250ml round bottomed flask. Add a porcelain piece and attach the same to a reflux condenser. Heat the mixture gently and keep in fume chamber. Add slowly in small portions 12.5ml of ni trobenzene; and after each addition shake the flask to ensure through mixing. After complete addition of nitrobenzene, heat the mixture with frequent shaking, on a boiling water bath for half an hour. Cool the mixture, and pour cautiously with vigorous stirring into 500ml of cold water; the dinitrobenzene soon solidifies. Filter at the pump, wash thoroughly with cold water and allow draining as completely as possible. Recrystallize a portion from rectified spirit. Record the melting point. 2. Preparation of m-nitroaniline Prepare a solution of sodium polyslphide by dissolving 40g of crystallized sodiumsulphide (Na2S.9H2O), in 150 ml water by adding 10g of finely powdered sulphur, and warming until a clear solution is produced. Heat a mixture of 25g of m-dinitrobenzene and 200ml of water in a one liter beaker until the water boils gently. Stir the solution mechanically. Place the sodium
sulphide solution in a dropping funnel and clamp the funnel so that the end of the stem is immediately above the beaker. Add sodium polysulphide solution during 30-45 minutes to the vigorously stirred boiling mixture, and boil gently for a further 20 minutes. Allow to cool more rapidly by adding ice. Filter the residue obtained at the pump and wash with cold water. Transfer the residue to 600ml beaker containing 10ml water and 35 ml con. Hydrochloric acid and boil for 15 minutes. m-nitroanile dissolves leaving the sulphur and any unchanged mdinitrobenzene. Filter and add excess of concentrated ammonia to the filtrate by which mnitroaniline is crystallized. Recrystallize a small portion from hot water. Record the yield and melting point. Organic preparation II (a) Preparation of tribromoaniline Dissolve 4 grams of aniline in four times its weight of glacial acetic acid in a beaker. Keep on a mechanical stirrer. Add from a burette drop by drop with stirring bromine dissolved in glacial acetic acid (1:2 ratios). The beaker must be cooled in ice during addition as the reaction is exothermic. The final product( a pasty mass) should be coloured yellow by addition of little more bromine if necessary. Pour into excess water, filter at pump, wash well with water press thoroughly and dry. Recrystallize a small portion from methylated spirit or rectified sprit, dry and determine the melting point. (120°). (b) sym.- tribromobenzene Dissolve 10 gram of sys.-tribromoaniline in 60ml of rectified spirit and 15 ml benzene in a 200ml bolt head flask by he ating on a wate r bath. Add from a burette3.5 ml of concentrate sulphuric acid to the hot solution and gently swirl the liquid. Attach a reflux condenser to the flask and heat on a water bathutill the cleat solution boils. Detach the condenser, remove the flask from the water bath, and add 3.5g of powdered sodium nitrite in two approximately equal portions; after each addition fit the condenser to the flask and shake the flask vigorously. The heat of the reaction will cause the solution to boil vigorously; when the reaction subsides, add the second portion of the sodium nitrite. Heat the flask on a boiling water bath as long as the gas is evolved; shake well from time to time. Allow the solution to cool for 10 minutes, and then immerse the flask in an ice bath. A mixture of tribromobenzene and sodium sulphate crystallizes out. Filter with suction on a buckner funnel, wash with a small quantity of alcohol, and then repeatedly with water to remove all the sodium sulphate. Dissolve the crude tribromobenzene in a boiling mixture of 120ml of glacial acetic acid and 30 ml of water, boil the solution with 2.5 gram of decolousrising carbon, and filter through a hot water funnel or pre heated buckner funnel: allow the solution to cool. Collect the crystals on Buckner funnel and wash with small quantity of chilled rectified spirit to remove the acetic acid. Dry in air upon filter paper. Record the yield and melting point (6.5g; 122°C)
ORGANIC ESTIMATIONS.
1.ESTIMATION OF ANILINE/PHENOL. Estimate the amount of aniline/phenol in the whole of the given solution. PRINCIPLE : Aniline reacts with bromine to give t ribromoaniline according to the equation.
Equivalent mass of aniline = molecular mass 6 = 72+7+14 6 = 15.5 The above equation is made use of in the estimation of aniline. Instead of using a standard bromine solution,a bromated-bromide mixture which easily liberate bromine in presence o f an acid is used. This is because the strength is not changed.
KBrO3+ 5 KBr+6HCl
6KCl+3Br2+3H2O
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% K I solution. It is titrated against sodium thiosulphate solution using starch as the indicator. Titration is repeated till concordant re sults are obtained. (b)Estimation of aniline/phenol. The given aniline solution is made up to 100 ml. 2 0 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 oc casional 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 o f bromine. The flask is shaken for 30 seconds and allowed to stand for 10 minutes.the stopper is removed and the neck of t he 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
=N1
Let 20 ml of brominating mixture
= V ml of Na2S2O3
Amount of brominating mixture used in the estimation
=40 ml
40 ml of brominating mixture
=2V ml of Na2S2O3
20 ml of aniline solution+40 ml of brominating mixture after reaction
= v2 ml of Na2S2O3
Amount of sodium thiosulphate equivalent to aniline
= (2V-V2) ml
Normality of Aniline
= (2V-V2)xN1x15.5 20x10
RESULT . Mass of aniline in the whole of the given
Solution
= ………….. g
2.Estimation of Ester Determine the percentage of ester in the given compound.
PRINCIPLE. Ester is hydrolysed 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, t he 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 o f the flask are quantitatively transferred into 250 ml standard flask and made up to mark. 25 ml of the solution is titrate d against N/2 HCl. From the titre value, percentage of ester in the given sample is calculated.
CALCULATION: Weight of ester
=Wg
Let the normality of NaOH be Let the normality of HCl be 50x N1 Volume of HCl =Unreacted NaOH V2x N2
= N1 =N2 = Volume of 1 N NaOH = V2 ml
=Volume of unreacted NaOHx Normality of NaOH
Volume of unreacted NaOH
= V2X N2 N1 =V3ml
V3XN1
=Volume of 1 N NaOH
Volume of 1N NaOH unreacted NaOH
= V3XN1 =V4 ml
Volume of 1N NaOH that has reacted 1000 ml 1 N NaOH = 1000 ml 1N ester
=V1-V4 =88 g of ester
(where 88 is the molecular weight of CH3-COOC2H5) 1 ml 1 N NaOH
= 88 g of ester 1000
(V1-V4) ml 1 N NaOH
= 88 (V1-V4) 1000 = W1 g
Percentage composition of ester
=W1X100 W
RESULT: The percentage composition of the ester=…………g
3.Estimation of iodine value of an ester Iodine value is a measure of t he degree of unsaturation of an oil.it is defined as the number of parts by mass of iodine absorbed by 100 parts by mass of an oil or fat.
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. 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 is estimated by titration with standard thiosulphate soklution. From the results the iodine value is calculated. 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 t he 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.
I Cl
+ KI KCl + I 2 ICl = 2I (b)Estimation: 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 tet rachloride. 25 ml of iodine monocghloride solution is then run in from a burette. The resulting mixture,if turbid, is cleared by adding more carbon t etrachloride. The bottle is gently rotated to m ix 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 o il 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 V 2 ml for reacting with the excess of iodine monochloride in the actual experiment, then the iodine value.
=
(V1-V2)x0.12692xSx100 w
S = The strength of thiosulphate W = Mass of oil taken. Result. Iodine value of the given oil = ……… .g
4.Determination of Ester value or saponification value of an oil or fat
Saponification value (ester value) is the number of milligrams of potassium hydroxide required to hydrolyse 1 gram of oil or fat or ester. Requirements: 1. N/2Alcoholic potash. 2.N/2 Hydrochloric acid PROCEDURE: About 1 to 2 g of ester(oil or fat) are weighed out accurately into around bottomed flask.The flask is fitted with reflux condenser .25ml of N/2 alcoholic potash are added and the flask is heated on wate r bath for about one hour.When reaction is complete,t he liquid becomes quit clear.
A blank experiment is done simultaneously with the same quantity of alcoholic potash.Both flasks are cooled and the alkali in both is e stimated by titration with N/2 hydrocholric acid using phenolphthalein as indicator.from the results the saponification value is calculated
CALCULATION Let V1 ml of N acid be required in the first experiment and V2 ml in the blank Then the alkali used up by the ester
=(V2-V1)ml
1 ml of N alkali
=56.1 mg of KOH
Hence saponification value
=56.1 (V2-V1) w
RESULT Saponification value of the given ester
= …………..g
ESTIMATION OF GLUCOSE AIM: To estimate the amount of glucose in the whole of the given solution PRINCIPLE: Alkaline solution of copper salts are reduced by aldose sugars to cuprous oxide.
R-CHO + 2Cu(OH)2
R-COOH + Cu2O + 2H2O
Since the reduction is not aromatic is not stoichiometric, the results are affected by slight variation in procedure. However results are trustworthy of standardisation also affected identical condition using solutions of pure sugar. 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 t he titration by adding so much of glucose solution that 0.5 ml t o 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 co lour. The titration is completed with in 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 m l. 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, repe at the titration and add so much of the glucose solution. So that 0.5 to 1 ml more is required to completethe 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 blueindicator. Complete the titration in 1 minute by adding glucose solution drop wise until the colour of methylene blue just disappears. Repeat the e xpt till the concordant value (+ 0.1 m l) are obtained. RESULT : Weight of glucose in the w hole of the given solution= ……………g
