FUNCTIONAL GROUP IDENTIFICATION 1. Reactions of amides: Action of NaOH: Amides are decomposed by NaOH to evolve ammonia. The gas can be tested by a moist red litmus paper which is then turned blue.
Amide
Sodium salt of carboxylic acid
Ammonia
Alkaline hydrolysis of aromatic amides to aromatic acid: The soluble sodium salt of aromatic acid formed from aromatic amides upon hydrolysis is regenerated as white precipitate in acidic medium.
Aromatic amide
Sodium salt of Aromatic Acid
Aromatic acid
Biuret Reaction for aliphatic diamide: When aliphatic diamide is heated at a temperature above its melting point ammonia is evolved and crystalline biuret is formed. This biuret in al!aline medium gives a violet colour with a drop of copper sulphate solution.
"iuret Hydroxamic acid test for aromatic primary amides: Hydrogen peroxide reacts with aromatic primary amides to form the hydroxamic acid which then reacts with ferric chloride to form ferric hydroxamate complex having a violet colour.
Aromatic amide
#erric hydroxamate $omplex
2. Reactions of caro!"#ic acids: Reaction with NaOH:$arboxylic acids being acidic dissolves in NaOH to form sodium salt. Action of NaHCO3: #orms salt with sodium bicarbonate solution with the evolution of carbon dioxide.
Fluorescein Reaction: The anhydrides of aromatic %&'dicarboxylic acids on heating with resorcinol gives a dye fluorescein. This dye in NaOH solution gives a yellowish red solution with green fluorescence.
Anhydride formation: Aromatic % & dicarboxylic acids decomposes to give its anhydride when heated at its melting point.
$. Reactions of %&eno#s: Action of neutral ferric chloride solution: (henol form characteristic coloured iron complexes when treated with neutral ferric chloride solution. )g phenol * resorcinol ' violet colour catechol'green etc.
Ao dye formation: Aryldia+onium salts react with aromatic rings of phenols to form highly coloured a+o compounds. These reactions are called coupling reactions.
Benoylation: (henols react with ben+oyl chloride in presence of NaOH to f orm esters.
'. Reactions of %rimar" amines: !iaotisation: At low temperature ,-'o$/ aromatic primary amines dissolved in strong acids ,H$l * H &SO0/ reacts with nitrous acid ,NaNO& 1H$l/ to form water soluble dia+onium salts. Aliphatic primary amines do not form stable dia+onium salts under similar condition. They react with nitrous acid to yield alcohols and nitrogen ,causes rapid foaming/.
Aryl dia+onium chlorire
Ao dye formation for aromatic primary amines: Aryldia+onium salts react with aromatic rings of phenols to form highly coloured a+o compounds. These reactions are called coupling reactions.
Benoylation: (rimary aromatic amines react with ben+oyl chloride in presence of NaOH replacing the H atom attached to the N atom with the ben+oyl group to give anilides.
Hins"er# reaction: Hinsberg
reagent
is
ben+enesulfonyl
chloride.
(rimary aliphatic amines on reaction with "en+enesulfonyl chloride * NaOH gives N'al!ylsulphonamide which contains an acidic hydrogen and hence dissolve in NaOH solution to form the soluble sodium salt. The solution thus obtained on acidification gives a precipitate of free sulfonamide which is insoluble in H$l.
(. Reactions of a#de&"des: Action of $chiff%s rea#ent: Schiff2s reagent is a red solution of rosaniline hydrochloride dissolved in water which is decolourised by passing
sulphur
dioxide.
3ilute solutions of aldehydes when added to Schiff2s reagent restores its red colour slowly.
Action of Borsche%s Rea#ent: Aldehydes reacts with &0'dinitrophenyl hydra+ine solution to give a orange4red precipitate of aldehyde &0'dintrophenylhydra+one derivative.
Action of &ollen%s Rea#ent: Aldehydes are oxidi+ed to carboxylic acids accompanied by the reduction of silver ions to metallic silver which appears as a mirror under proper conditions.
Action of sodium "isulphite solution:
Saturated solution of sodium bisulphite in water when mixed with aldehydes gives a white crystalline bisulphite addition compounds.
). Reactions of *etones: Action of Borsche%s Rea#ent: 5etones reacts with & 0 dinitrophenyl hydra+ine solution to give an orange4red precipitate of !etone &0 dintrophenylhydra+one derivative.
Action of sodium nitroprusside solution6 The nitroprusside ion which may be regarded as a special carrier of the nitrosonium ion forms a coloured complex with methyl !etones. 7n presence of al!ali eg acetone is converted to $H 8$O$H&' ion which reacts with nitroprusside ion 9#e,$N/NO:&' to give highly coloured ion 9#e,$N/ NO$H&$O$H8:&'.
Identification of f+nctiona# ,ro+%s:
Experiment 'nference %(
Action
of
sodium
hydroxide a. Ammonia is evolved.
solution
(resence of amides.
b. Substance dissolved. White crystalline ppt.
(resence
of
acidic
substances. (resence
of
aromatic
amides. )(
Action To
a
of
few
ml
NaHCO 3
of
the
saturated "ris!
effervescence
with
the (resence of acids.
NaH$O8 solution ta!en in a test tube aliberation of $O&. little of the substance is added. 3(
Action
of
FeCl3 solution.
To a little of the substance in water or ;iolet colour. alcohol
a
few
drops
of
(resence of phenols.
neutral
#e$l8solution is added. *(
Action
of
$chiff%s
rea#ent ;iolet colour developed within & (resence of aldehydes. minutes.
+(
Action
of
Borsche%s
rea#ent( A yellowish orange ppt.
(resence of aldehydes or !etones.
,(!iaotisation con H$l cool in ice.
(resence
of
primary
aliphatic amines(
-(
Confirmatory &ests for Functional .roups: &ests for aldehydes:
-( Action of &ollen%s rea#ent: "lac! ppt. A little of the substance is boiled with few drops of Tollen2s reagent. )(
Action
of
sodium
"isulphite
(resence of aldehyde
solution:
Two drops of the aldehyde is sha!en with White crystalline ppt.
(resence of aldehyde
saturated solution of NaHSO8 &ests for ketones: -(
Nitroprusside test: Add a few drops of sodium nitroprusside Wine red colour. solution to few drops of !etone. Then add NaOH solution in excess. &est for acids:
(resence of methyl !
-(Fluorescein Reaction: A little of the substance is heated with A red solution $onc.H &SO0 *
Anhydride
with
intense
green(resence of dicarbox
formation: White shiny needles are deposited on the(resence of dicarbox
A little of the acid is heated in a dry china dishsides of the funnel. covered with an inverted funnel whose stem is closed. 7t is then cooled. &ests for amides: -(
Biuret reaction: A little of the substance is heated first gently On heating smell of ammonia is evolved *(resence of diamide. in a dry test tube followed by strong heating. The solid residue is warmed with% ml %-= NaOH thenviolet colour on adding $uSO 0. cooled and one drop of dil.$uSO0 added. )
(
Hydroxamic
acid
test:
(lace a little of the substance in ml water. >agenta colour. Add few drops 8= hydrogen peroxide and & drops
(resence
of
arom
amide.
of = ferric chloride. Heat the solution. &est for aromatic amines /primary0: %. Add &ml of cold dia+onium solution to a solution of -.%g & 'naphthol in &ml %-= NaOH. * ml Orange ?red dye.
(resence of
water. A white ppt is formed. )(
(resence of
Benoylation: 3issolved a little of the substance in %-ml
%-=NaOH solution contained in a boiling tube. About %ml of
ben+oyl chloride is added. The
boiling tube is cor!ed and sha!en vigorously for about % minutes. &est for aliphatic amines /primary0: %.a. To -.8 m@ or 8-- mg of un!nown substance in a test tube add m@ of %-= NaOH solution and -.0 m@ of ben+enesulfonyl chloride. $lose the test tube Soluble in base.
(resence
with a cor! and sha!e the mixture vigorously. Test
amines(
o
the solution to ma!e sure that it is still al!aline A precipitate is f ormed. using litmus paper.
(resence
b. $ool the solution * add %-= H$l solution
amines(
dropwise.
o
&ests for aromatic alcohol /1henol0: -(
Ao2dye formation: 3issolve two drops of aniline in % ml dil.H$l A red coloured substance is formed. well cooled in ice. #ew drops of saturated sodium nitrite solution are added. Then it is added to a well cooled solution of the phenolic compound in aueous sodium hydroxide. )
(resence of phenol
(Benoylation: 3issolved a little of the substance in ml A white ppt is formed.
&-=NaOH solution contained in a boiling tube. About %ml of
ben+oyl chloride is added. The
boiling tube is cor!ed and sha!en vigorously for about % minutes.
(resence of phenol
