question_answer 11)

Give one chemical test to distinguish between the followingpairs of compounds. (i) Methylamine and dimethylamine (ii) Secondary and tertiary amines (iii) Ethylamine and aniline     (iv) Aniline and benzylamine (v) Aniline and N-methylaniline.   (a) Write the structures of amines and classify them into  benzyl amine or aromatic amine. (b) Only  amines (all types) give carbylamine reaction. and aliphatic amines give Libermann?snitrso reaction. (c) Aromatic amines give dye test. i.e., diazotization followed by coupling.  

Answer:

(i) Methylamine and dimethyl amine or isocyanide testMethyl amine (primary) responds to carbyl amine reaction. Whenheated with chloroform and KOH, it produces foul smell. Dimethylamine (secondary) does not respond to this test. (ii) Secondary and tertiary amines Libermann?s nitroso reactionSecondary amines (both aliphatic and aromatic) react with nitrousacid to form nitrosoamines (yellow oily liquid) When the yellow oily liquid is warmed with a crystal of phenol and a few drops of cone. agreenish solution is formed, It changes to red on dilution with water but changes to deep blue onaddition of aqueous  solution. Tertiary amines do not give this test. (iii) Ethyl amine and aniline Ethyl amine (primary aliphatic amine)and aniline (primary aromatic amine) can be distinguished by azodye test Aniline responds to this test whereas ethyl amine does not.   (iv) Aniline and benzyl amine (nitrous acid test) Benzyl amine reactswith nitrous acid to form a diazonium salt which is unstable. Itevolves  gas by decomposing at even low temperature. Aniline reacts with nitrous acid to from benzene diazonium chloride which does not decompose to give. (v) Aniline and N-methylaniline (carbylamine test) Aniline givecarbylamine test because it is a primary amine whereas N-methyl aniline (secondary amine) does not give this test.