Question

Give one chemical test to distinguish between the following pair of compounds.

Ethylamine and aniline

Answer 1

Ethylamine is a primary aliphatic amine, while aniline is a primary aromatic amine. They can be differentiated by azo dye test.

Azo dye test: In this, aromatic primary amine reacts with HNO₂ (NaNO₂ + dil. HCl) at 273 – 278 K and then reacts with alkaline solution of 2-naphthol (β-naphthol) to give a deep yellow, orange or red colored dye.

Aliphatic primary amines under the above conditions rapidly release nitrogen gas with the formation of primary alcohols, i.e., the solution remains transparent.

$$\underset{\mathrm{Ethylamine}}{\mathrm{C}{\phantom{A}}_2\mathrm{H}{\phantom{A}}_5\mathrm{NH}{\phantom{A}}_2}+\mathrm{HONO}\stackrel{273-278\mathrm{K}}{\to }\underset{\mathrm{ethyl}\mathrm{alcohol}}{\mathrm{C}{\phantom{A}}_2\mathrm{H}{\phantom{A}}_5\mathrm{OH}}+\mathrm{H}{\phantom{A}}_2\mathrm{O}+\mathrm{N}{\phantom{A}}_2\uparrow$$