Question

Give one chemical test to distinguish between the following pairs of compounds.
(i) Methylamine and dimethylamine

(ii) Secondary and tertiary amines

(iii) Ethylamine and aniline

(iv) Aniline and benzylamine
(v) Aniline and N-methylaniline.

Answer 1

(i) Methylamine and dimethylamine :
Carbylamine test.
Methylamine, on heating with alc. KOH solution and chloroform form foul-smelling methyl isocyanide. This test is not given by dimethylamine.
(ii) Secondary and tertiary amines :
Secondary amines give Libermann nitrosoamine test.
On heating with nitrous acid (prepared in situ), they give yellow coloured oily N-nitrosoamine.
Tertiary amines do not give such test.
(iii) Ethylamine and aniline :
Azo dye test.
Aniline on diazotization ( ice cold nitrous acid solution) followed by coupling with 2-naphthol (in alkaline solution) forms brilliant orange or red dye. Ethylamine will not form dye. It will give brisk effervescence (due to liberation of nitrogen gas) but solution remains clear.
(iv) Aniline and benzylamine :
Azo dye test.
Aniline on diazotization ( ice cold nitrous acid solution) followed by coupling with 2-naphthol (in alkaline solution) forms brilliant orange or red dye. Benzylamine will not give such test.
(v) Aniline and N-methylaniline :
Carbylamine test.
Aniline, on heating with alc. KOH solution and chloroform form foul-smelling methyl isocyanide. This test is not given by N-methyl aniline.