Question

The amine 'A' when treated with nitrous acid gives a yellow oily substance. The amine ‘A’ is:

• A. Tri ethyl amine
• B. Tri methyl amine
• C. Aniline
• D. Methyl phenyl amine

Answer 1

The correct option is D

Methyl phenyl amine

Explanation of correct option

Secondary (2°)amines [Methylphenylamine]react with ${\mathrm{HNO}}_2$producing an insoluble oil (N-Nitrosoamine)

$\underset{\mathrm{Methylphenylamine}}{\mathrm{Ph}-\mathrm{NH}-{\mathrm{CH}}_3\left(\mathrm{aq}\right)}+\underset{\mathrm{nitrous}\mathrm{acid}}{\mathrm{HO}-\mathrm{N}=\mathrm{O}\left(\mathrm{aq}\right)}⟶\underset{\mathrm{N}-\mathrm{Nitrosoamine}}{\mathrm{Ph}-\mathrm{N}\left({\mathrm{CH}}_3\right)-\mathrm{N}=\mathrm{O}\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

Explanation of Incorrect option.

(C) - Aniline.

Aniline reacts with nitrous acid to form phenol.

(A) -Tri ethyl amine

The result is different in this case. Here nothing special happens and you are left with a colourless solution.

There is a formation of an ion by reaction with an acid present.

(B) - Tri methyl amine

The result is different in this case. Here nothing special happens and you are left with a colourless solution.

There is a formation of an ion by reaction with an acid present((Ammonium Salt Formation)

Tertiary(3°) amines[Like Triethylamine and trimethylamine] react with ${\mathrm{HNO}}_2$produces a clear solution (Ammonium Salt Formation)

Hence, Option(D) is correct.