Detection of functional group in given organic compound carbohydrate
Answers
Reactions of amides:
Reaction 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.
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.
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 alkaline medium gives a violet colour with a drop of copper sulphate solution.
Biuret reaction
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.
Reactions of carboxylic acids:
Reaction with NaOH:
Carboxylic acids being acidic dissolves in NaOH to form sodium salt.
Reaction of NaHCO3:
Forms salt with sodium bicarbonate solution with the evolution of carbon dioxide.
Fluorescein Reaction:
The anhydrides of aromatic 1,2-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 1,2-dicarboxylic acids decomposes to give its anhydride when heated at its melting point.
Reactions of phenols:
Reaction of neutral ferric chloride solution:
Phenol form characteristic coloured iron complexes when treated with neutral ferric chloride solution. E.g. phenol & resorcinol - violet colour, catechol-green etc.
Azo dye formation:
Aryldiazonium salts react with aromatic rings of phenols to form highly coloured azo compounds. These reactions are called coupling reactions.
Benzoylation:
Phenols react with benzoyl chloride in presence of NaOH, to form esters.
Reactions of primary amines:
Diazotisation:
At low temperature (0-5oC) aromatic primary amines dissolved in strong acids (HCl & H2SO4) reacts with nitrous acid (NaNO2 +HCl) to form water soluble diazonium salts.
Aliphatic primary amines do not form stable diazonium salts under similar condition. They react with nitrous acid to yield alcohols and nitrogen (causes rapid foaming).
Azo dye formation for aromatic primary amines:
Aryldiazonium salts react with aromatic rings of phenols to form highly coloured azo compounds. These reactions are called coupling reactions.
Benzoylation:
Primary aromatic amines react with benzoyl chloride in presence of NaOH, replacing the H atom attached to the N atom with the benzoyl group to give anilides.
Hinsberg reaction:
Hinsberg reagent is called benzenesulfonyl chloride. Primary aliphatic amines on reaction with benzenesulfonyl chloride & NaOH gives N-alkylsulphonamide 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 HCl.