Organic Chemistry Practical Manual - Compound Identification

SYSTEMATIC PROCEDURE FOR IDENTIFICATION OF THE FUNCTIONAL GROUP OF AN ORGANIC COMPOUND S. No. Experiment 1 Physical Characteristics: a) State b) Colour c) Odour 2

Solubility: a) Cold Water (Test the aqueous solution with Blue and Red Litmus Papers)

Observation

Inference

Solid/liquid Colourless/ _ _ _ _ _ colour Pleasant/ phenolic/ aniline like/ oil of bitter almond/ characteristic Soluble Blue Litmus turned to Red Red Litmus turned to Blue

Acidic Basic Presence of Carboxylic Acid b) NaHCO3 (10%) Soluble with effervescence Group Presence of Acidic Substance c) NaOH (10%) Soluble (Acids and Phenols) Presence of Basic Substances d) dil HCl (10%) Soluble (Amines) Note: 1) If Water Soluble, do not test with NaHCO3, NaOH and dil HCl. Use Litmus Paper 2) If the Compound is insoluble in water and the other reagents, it is NEUTRAL

e) Ether (Note: Insoluble in water, acid and alkali)

3.

Flame Test: Glass rod is dipped in the compound and subjected to flame

4.

Hydrocarbons, nitrohydro carbons, alkyl or aryl halides, Soluble esters and ethers. Higher molecular weight alcohols, aldehydes and ketones Insoluble in Ether but soluble May be Carbohydrates or in water Urea

Test for Unsaturation: a) Baeyer’s Test: Compound is added to aq. KMnO4 solution b) Compound is added to Bromine in CCl4 (2%)

a) Burns with a sooty flame

Aromatic

b) Burns with nonsooty flame

Aliphatic

c) Charring

Carbohydrates, etc

a) Decolourisation of KMnO4 with brown ppt. b) Decolourisation of Br2 without evolution of HBr The compound decolourises both the reagents The compound does not decolourise the two reagents (OR) The colour of one reagent is discharged and the colour of the other is not

Unsaturated Saturated

Saturated

Dr. S. Paul Douglas, Dept. of Engineering Chemistry, A. U. College of Engg. Andhra University 1

Br Br C C

(Vicinal Dibromide)

C C

+ Br 2 (Brown)

(Clear)

OHOH

C C

+ KMnO 4

C C

+ MnO 2

(Glycol)

(Brown)

(Purple)

5.

Lassaigne’s Test for Extra Elements: (Nitrogen and Halogens) A small piece of Sodium metal (Freshly cut) is placed in an ignition tube and the tube is heated strongly. Small quantity of the compound (one or two crystals if solid or one or two drops if liquid) is added and the tube heated strongly. The red hot tube is plunged into 10.0ml of distilled water contained in a mortar and is crushed with pestle and the solution filtered. The filterate is called Sodium Fusion Extract. S. No. Experiment Observation Inference a) Test for Nitrogen: (in the form of NaCN in the Extract) To small quantity of the extract If the colour of the solution after few crystals of Mohr’s salt are adding dil H2SO4 is intense blue Nitrogen Present (Prussian Blue) added and boiled. To this solution dil H2SO4 is added to get clear solution

Na+C+N®NaCN 6NaCN + FeSO 4®Na 4 [Fe(CN) 6 ] + Na 2 SO 4 Na 4 [Fe(CN) 6 ]+ 2Fe 2 (SO4) 3 ® Fe 4 [Fe(CN) 6 ] 3 + 6Na 2 SO 4 (Prussian Blue Clour) b) Test for Halogens: The Sodium Fusion Extract is acidified with dil HNO3, boiled, cooled and AgNO3 solution is added

a)White Precipitate soluble in NH4OH b) Cream coloured Precipitate , sparing soluble in NH4OH c) Yellow Precipitate insoluble in NH4OH

Chlorine Present Bromine Present Iodine Present

Na+Cl/Br/I ®NaCl/NaBr/NaI NaX + AgNO 3 ® AgX (ppt) + NaNO 3 c) Test for Sulphur: The Black precipitate of PbS is extract is acidified with acetic obtained acid and Pb(CH3COO)2 solution

Sulphur is Present

2Na+S®Na2S Pb(CH3COO)2 + Na2S ® PbS + 2 CH3COONa

(ALL THE ABOVE TEST ARE COMPULSORY FOR ANY GIVEN COMPOUND)


Tests for Functional Group Identification S. No. Experiment Observation Inference Carboxylic Acids: (Acidic, Soluble in NaHCO3 and NaOH) CO2 gas is evolved Carboxylic acid group present 1 Add 1 ml of saturated NaHCO3 solution to one drop of liquid or small amount of solid one drop of liquid or small amount of solid is dissolved in Fruity Odour is observed 5ml of ethyl alcohol and 2drops Carboxylic acid group is present (due to the formation of esters of conc. H2SO4 are added and which are sweet smelling) the mixture is poured in to 25ml of dil Na2CO3 and stirred well (Carboxylic Acids do not have any characteristic tests other than its solubility in NaHCO3 with effervescence and NaOH. To know whether the acid is simple acid or phenolic acid test with FeCl3) Phenols: (Acidic, Insoluble in NaHCO3 2 but soluble in NaOH) a) Test with FeCl3 A prominent Colour change The compound is dissolved in other than the yellow colour of Phenolic hydroxyl group present 1ml of alcohol or suspended in FeCl3 obtained water and one or two drops of (Usually blue or violet – some dilute FeCl3 added cases red or green) b) Liebermann’s Nitroso Test Compound is added few crystals of NaNO2 , warmed very A deep blue or deep green gently for 20 seconds and colouration developed slowly Phenolic hydroxyl group present allowed to cool and twice the volume of Conc. H2SO4 added (Note: Only some Phenols give and rotate the test tube slowly to this test as mentioned above) mix Dilute the contents cautiously The solution turns red with water Now add an excess of NaOH The green or blue colouration Solution reappears (Note: Phenols where Para Position is vacant only will give Liberman’s Niroso Test) 3 Alcohols: a) Ceric ammonium nitrate test: To the aqueous solution of Alcoholic hydroxyl group Red colour observed the compound. Add few drops present of ceric ammonium nitrate b) Xanthate test: to the aqueous solution add pellets of Yellow precipitate formed Alcoholic group present KOH, heat, cool and then add 1.0ml of ether followed by 23 drops of CS2 Non insoluble layer separates at 1 0 Alcohol c) Distinction between 1 0 , 2 0 once and 3 0 alcohols: To 2 ml of the Cloudiness appears after 45 2 0 Alcohol compound 8ml of Lucas reagent minutes added and shake Solution remains clear 3 0 Alcohol


S. No. Experiment Observation 4 Carbohydrates: (Soluble in Water, Neutral, Aliphatic and NonNitrogenous) a) Molisch’s Test: The compound is dissolved in water and 23 drops of 1% A deep violet coloration is alcoholic solution of anaphthol produced where the two liquids and then carefully pour 2 ml of meet conc. H2SO4 down the side of the test tube so that it forms a heavy layer at the bottom b) Action of H2SO4: The The compound immediately compound is warmed with 1 ml blackens. As the temperature of Conc. H2SO4 on a small raises, CO2 , CO and SO2 are flame evolved c) To a small amount of the compound, Fehling’s Reagent is Red precipitate of CuO2 is added and heated on a water obtained bath 5 Carbonyl Compounds: (Neutral Compounds) a) Test with Borsch’s Reagent: Few drops of the compound is dissolved in methanol and a few Yellow or Orange coloured drops of 2,4dinitrophenyl Precipitate is formed hydrazine reagent are added (gently heat and cool if necessary)

R H or R'

O + H 2 NHN

NO 2

Inference

Carbohydrate present

Carbohydrate present

Reducing sugar

May be aldehyde or ketone

R NHN H or R'

O 2 N b) Tollen’s Test: In a clean test tube 23 ml of AgNO3 solution is taken and 23 drops of NaOH soln. added. To this dil. Ammonia added drop by drop until the precipitated silver oxide is almost redissolved, then few drops of A silver mirror is formed the compound added the mixture is gently warmed on a water bath with vigorous shaking from time to time

NO 2

O 2 N

Aldehyde group present


S. No.

Experiment c) Fehling’s Test:

Observation

Inference Aldehyde group present

To 1 ml of the compound 1 ml of 10% Na2CO3 solution and a few drops of Fehling;s solution are added and mixture is boiled gently for 1 minute

The solution usually turns green (Aliphatic aldehydes reduce and on standing a fine yellow or Fehling’s solution rapidly, red precipitate of cuprous oxide Benzaldehyde slowly and slowly separates out Salicylaldehyde does not reduce it)

d) Schiff’s Test The compound is added to the decolourised Schiff’s Reagent.

6

The Schiff reagent is the reaction product of Fuchsine (pararosanilin) and sodium bisulfite

A characteristic magenta or purple colour develops

Tests for Ketones:

(Ketones do not give Tollen’s, Fehling’s and Schiff’s test)

Aldehyde group present

a) Aliphatic ketones containing CH3CO– group restore the colour very slowly to Schiff’s reagent. Other ketones have no reaction. b) Ketones containg the CH3CO– group give the Iodoform test and a red colouration with alkaline sodium nitroprusside and a violet colouration with mdinitrobenzene and sodium hydroxide Esters: (Neutral) a) Hydroximic Acid Test: To a few drops of the ester 0.2g of hydroxylamine hydrochloride and 5 ml of 10% NaOH solution are added and gently boiled for 12 minutes. The mixture is A violet or deep redbrown Ester group present cooled and acidified with HCl, colour develops immediately cooled again and the a few drops of FeCl3 solution are added b) Hydrolysis to Acid: 2 ml of the compound is taken in a 50 mol RB flask fitted with reflux watercondenser and 20 ml of 10% aq. NaOH soln. and refluxed for 2030 minutes till a Solid acid derivative is obtained Ester group present homogeneous clear solution is obtained. The mixture is cooled and acidified with HCl (Note: For Phenolic Esters do not perform hydroxymic acid test )


S. No. Experiment Observation Primary Amines: (Soluble in HCl, Basic, Nitrogenous) 7 a) Isocyanide Reaction / Carbylamine Test: A foul odour of isocyanide To 0.2g of the substance a few (carbylamine) is produced drops of chloroform and 23 ml Note: of ethanolic NaOH soln are (Cool the tube and carefully add added, mixed well and warmed an excess of conc. HCl to gently deodorise by converting the isocyanide to amine) b) Diazotisation Test: 0.2g of the compound is dissolved in 1 ml of conc. HCl and diluted with 3 ml of H2O, cooled in ice and a few drops of sodium nitrite soln. are added. This cold diazonium solution is A brilliant red dye is produced added to a cold solution of bNaphthol in excess of 10% NaOH solution Secondary Amines: (Soluble in HCl, Basic, Nitrogenous) A little compound is dissolved A deep blue or deep green in 3 ml of dil. HCl and sodium colouration developed slowly. nitrite soln with cooling is added On dilution the solution turns gradually with shaking until the red yellow oily ppt. of Nitrosoamine On adding excess NaOH the obtained green or blue colouration reappears Libermann’s test: To small quantity of Nitrosoamine add 1 or 2 drops of Phenol and continue the test as in 2b given previously Tertiary Amines: (Soluble in HCl, Basic, Nitrogenous) a)pNitroso derivative test 0.2g of the compound is dissolved in 3 ml of dil. HCl, it is chilled in ice and then 2 ml of A reddish solution obtained but 20% sodium nitrite soln added no oil separates. Allow to stand carefully drop by drop. for 5 min. in the cold. Then NaOH solution is added b) Potassium Ferrocyanide Test: The compound is dissolved in dil HCl and aq. Solution of K4Fe(CN)6 is added to it

Inference

Primary amine Present

Primary amine is confirmed

Secondary Amine Confirmed

Tertiary amine Present

A green colour is obtained.

Bulky white precipitate is obtained

Tertiary Amine Confirmed


S. No. Experiment Observation Inference Nitro Compounds: (Neutral, Nitrogenous) 8 a) The compound is taken in a boiling tube and 5 ml of conc. HCl and several pieces of Tin added to it. The mixture is warmed and shaken continuously to break up the oily drops of the nitro compound. To the residue conduct tests for Primary Amines b) Mulliken and Barker’s reaction: The compound is added and to 10.0 ml of 50% alcohol and 0.5 g of Zn dust and 0.5 g of NH4Cl/ CaCl2. The mixture is boiled for 5 minutes and filtered. i) The filtrate is added Tollen’s Black Precipitate or Silver Nitro group present reagent (A+B) mirror is formed RNO2 + 4H ® RNHOH + H 2 O

RNHOH + 2[Ag(NH3)2]OH ® RNH + 2Ag+ 4NH3 + 2H2O

9

10

ii) The filtrate is added Red Precipitate of Cu2O is Fehling’s solution (A+B) and Nitro group present formed heated on a water bath Amides and Anilides: (Neutral, Nitrogenous) Compound is Strongly heated a) Smell of ammonia gas turning Amide group present with conc. NaOH moist red litmus paper blue RCONH2 + NaOH ® RCOONa + NH 3 b) Smell of aniline (Confirm the formation of Anilide Present aniline by doing carbylamine test) RCONHPh + NaOH ® RCOONa + PhNH2 Biuret Test for Urea: A little of the substance is gently heated in a dry test tube until it melts and then solidifies. The residue A violet colour is produced Presence of a diamide like Urea is dissolved in a little water, and a dil. Solution of CuSO4 followed NaOH drop by drop are added Hydrocarbons (Neutral) Note: This test should be done only after proving the absence of other functional groups The compound is shaken with conc. H2SO4 till a clear solution a) Compound did not regenerate Hydrocarbon Present is obtained. The contents are warmed if necessary while Ether Present dissolving. b) Compound regenerated The clear solution is poured over ice

REPORT: The given Compound is: Neutral/ Acidic/ Basic Aromatic/ Aliphatic Saturated/ Unsaturated Extra Element/s Present: Functional group/s Present: M.P/ B.P


The Functional Groups to be identified are: A)

B)

C) D)

1. Carboxylic acid / Substituted Aromatic Carboxylic Acids 2. Phenols / Substituted Phenols 3. Alcohols 4. Carbonyl Compounds – Aldehydes and Ketones 5. Esters / Phenolic Esters 6. Carbohydrates 7. Hydrocarbons / Halogenated Hydrocarbons 8. Ethers 9. Amines 1 0 or Primary / 2 0 or Secondary / 3 0 or Tertiary 10. Nitro Compounds 11. Amides 12. Anilides

Acidic Substances without Nitrogen

Neutral Compounds without Nitrogen

Basic Nitrogen Containing Compounds Neutral Nitrogen Containing Compounds


THE PREPARATION OF DERIVATIVES OF ORGANIC COMPOUNDS The preliminary examination and group classification tests indicate the particular class (functional group) to which an unknown organic compound may belong. Further characterisation and identification depends on the selection and preparation of a suitable solid derivative and accurate determination of its melting point (best, between 90 150 ). The following table lists some of the classes of organic compounds and a selection of derivatives that may be prepared to characterise them. Check with the tables of melting points in Vogel which derivatives are most suitable for the characterisation of your particular compound. CLASS OF COMPOUND 1. ALCOHOLS 2. PHENOLS 3. ALDEHYDES AND KETONES 4. ACIDS 5. AMINES

DERIVATIVES 3,5dinitrobenzoate benzoate, acetate, bromoderivative semicarbazone, 2,4dinitrophenyl hydrazone, oxime anilide, amide, ptoluidide. benzoyl, acetyl and sulphonamide derivatives

METHODS FOR THE PREPARATION OF DERIVATIVES 1. ALCOHOLS: (i) 3,5Dinitrobenzoates 3,5Dinitrobenzoyl chloride is usually partially hydrolysed and should be prepared in the pure state by heating gently a mixture of 3,5dinitrobenzoic acid (1 g) and phosphorus pentachloride (1.5 g) in a dry test tube, until it liquifies (5 min).* The liquid is poured on a dry watch glass and allowed to solidify. The phosphoryl chlorides are removed by pressing the solid with a spatula on a wad of filter paper. The residual acid chloride is suitable for immediate use in the preparation of the derivatives. The 3,5dinitrobenzoyl chloride is mixed with the alcohol (0.5 1 mL) in a loosely corked dry test tube and heated on a steam bath for about 10 min. Secondary and tertiary alcohols require up to 30 min. On cooling add 10 mL sodium hydrogen carbonate solution, stir until the ester crystallises out, and filter at the pump. Wash with a little carbonate solution, water and suck dry. Recrystallise from the minimum hot ethanol or light petroleum. Cool slowly to avoid the formation of oily droplets of your ester.(*Work under fume hood. Fumes are irritating to the eyes and nose.) 2. PHENOLS (i) Benzoates (SchöttenBaumann method). To the phenol (0.5 g) is added 5% sodium hydroxide (10 mL) in a wellcorked boiling tube or a small conical flask. Benzoyl chloride (2 mL) is added in small quantities at a time, and the mixture shaken vigorously with occasional cooling under the tap or in icewater. After 15 min the solid benzoate separates out: the solution should be alkaline at the end of the reaction; if not alkaline, or if the product is oily, add a solid pellet of sodium hydroxide and shake again. Collect the benzoate, wash thoroughly with cold water, and recrystallise from alcohol or light petroleum. (ii) Acetates Acetates of many simple phenols are liquids; however, this is a suitable derivative for polyhydric and substituted phenols. The phenol (0.5 g) is dissolved in 10% sodium hydroxide solution and an equal quantity of crushed ice is added, followed by acetic anhydride (2 mL). The mixture is vigorously shaken in a stoppered test tube until the acetate separates. The product is filtered and recrystallised from alcohol. Dr. S. Paul Douglas, Dept. of Engineering Chemistry, A. U. College of Engg. Andhra University 9

(iii) Bromo derivatives The phenol (0.3 g) is suspended in dilute hydrochloric (10 mL) and bromine water added dropwise until no more decolourisation occurs. The bromo derivative which precipitates out is filtered off and recrystallised from alcohol. 3. ALDEHYDES AND KETONES (i) Semicarbazones Dissolve semicarbazide hydrochloride (1 g) and sodium acetate (1.5 g) in water (8 10 mL), add the aldehyde or ketone (0.3 mL) and shake. Shake the mixture for a few minutes and then cool in icewater. Filter off the crystals, wash with a little cold water and recrystallise from methanol or ethanol. (ii) 2,4Dinitrophenylhydrazones Suspend 0.25 g of 2,4dinitrophenylhydrazine in 5 mL of methanol and add 0.5 mL of concentrated sulphuric acid cautiously. Filter the warm solution and add a solution of 0.2 g of the carbonyl compound in 1 mL of methanol. Recrystallise the derivative from methanol, ethanol or ethyl acetate. (iii) Oximes Hydroxylamine hydrochloride (0.5 g) is dissolved in water (2 mL). 10% sodium hydroxide (2 mL) and the carbonyl compound (0.2 0.3 g) dissolved in alcohol (1 2 mL) are added, the mixture warmed on a steam bath for 10 min and then cooled in ice. Crystallisation is induced by scratching the sides of the test tube with a glass rod. The oximes may be crystallised from alcohol. 4. ACIDS (i) Amides, anilides and ptoluidides The acid (0.5 g) is refluxed with thionyl chloride (2 3 mL) in a fume cupboard for about 30 mins.* It is advisable to place a plug of cotton wool in the top of the reflux condenser to exclude moisture. The condenser is removed and the excess of thionyl chloride is distilled off (b.p. 78 ). The acid chloride thus produced is treated with concentrated ammonia solution (5 mL) or aniline (0.5 1 mL) or ptoluidine (0.5 1 g), when the solid derivative separates out. It is collected and recrystallised from alcohol adding decolourising charcoal if found necessary. *Alternately use PCl5 to form the acid chloride. 5. AMINES (i) Acetyl derivatives (acetamides) Reflux gently in a small dry flask under a dry condenser the amine (1 g) with acetic anhydride (3 mL) for 15 min. Cool the reaction mixture and pour into 20 mL cold water. Boil to decompose the excess acetic anhydride. Cool and filter by suction the insoluble derivative. Recrystallise from ethanol. (ii) Benzoyl derivatives (benzamides) Suspend 1 g of the amine in 20 mL of 5% aqueous sodium hydroxide in a wellcorked flask, and add 2 mL benzoyl chloride (fume hood!), about 0.5 mL at a time, with constant shaking. Shake vigorously for 5 10 min until the odour of the benzoyl chloride has disappeared. Ensure that the mixture remains alkaline. Filter off the solid derivative, wash with a little cold water and recrystallise from ethanol. (iii) Benzenesulphonamides To 1 g of the amine in 20 mL of 5% sodium hydroxide solution in a wellcorked flask add 1 mL benzenesulphonyl chloride (fume hood!). Shake the mixture until the odour of the sulphonyl chloride disappears. Check that the solution is alkaline. Acidify if necessary to obtain the precipitated derivative. Concentrated hydrochloric acid added dropwise should be used. Filter the product, wash with a little cold water and suck dry. Recrystallise from ethanol. Dr. S. Paul Douglas, Dept. of Engineering Chemistry, A. U. College of Engg. Andhra University 10

Organic Chemistry Practical Manual - Compound Identification

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