Question

Give a chemical test to distinguish between ethylamine and aniline.

Answer 1

Aniline responding to nitrous acid (${\mathrm{HNO}}_2$) and azo-dye test:-

1. Aniline$\left({\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{NH}}_2\right)$ is an aromatic amine.
2. Aromatic amines on treating with nitrous acid form a stable compound called diazonium salt
3. In the first step, aniline is reacted with nitrous acid at a low temperature$(273\mathrm{K}-278\mathrm{K})$, and a diazonium salt of benzene diazonium chloride is formed:
4. The benzene diazonium chloride formed, is then reacted with 2-napthol$\left({\mathrm{C}}_{10}{\mathrm{H}}_8\mathrm{O}\right)$ in presence of sodium hydroxide$\left(\mathrm{NaOH}\right)$ having a pH of 9-10 to form an orange dye of 1-phenylazo-2-napthol:

Ethylamine responding to nitrous acid-

1. Ethylamine is an aliphatic primary amine.
2. When ethylamine is treated with nitrous acid$\left({\mathrm{HNO}}_2\right)$ at a low temperature$(273\mathrm{K}-278\mathrm{K})$, a brisk effervescence of nitrogen gas$\left({\mathrm{N}}_2\right)$ is observed, along with the formation of ethanol$({\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{OH})$ and hydrochloric acid$\left(\mathrm{HCl}\right)$:

Therefore, we can distinguish between ethylamine and aniline with help of the nitrous acid and the azo-dye test.