Question

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

• A. triethylamine
• B. trimethylamine
• C. aniline
• D. methylphenylamine

Answer 1

Answer: (D)

Secondary amines when treated with nitrous acid give yellow oily substance. So, amine ' $A'$ is methylphenyl amine.

Reaction of nitrous acid with allphatic amines

Liberation of $N _{2}$ gas $+$ alcohol formation

$R- NH _{2}+ HNO _{2} \longrightarrow R-\stackrel{+}{ N } \equiv NCl ^{-}$

$\stackrel{ H _{2} O }{\longrightarrow } ROH + N _{2}+ HCl$

Reaction of nitrous acid with aromatic amines

Liberation of $N _{2}$ gas $+$ Phenol formation

$PhNH _{2}+ H NO _{2} + HCl \stackrel{273-278 K }{\longrightarrow }$

$Ph - \overset{+}{N} \equiv NCl ^{-} \longrightarrow PhOH + HCl + N _{2}$

Reaction of nitrous acid with $2^{\circ}$ amines With $HNO _{2}$, they give nitroso amines, which being insoluble in dilute acids separate as yellow oily compound.

$R_{2} NH + HONO \longrightarrow R_{2}- N - N = O$

N-nitroso dialkyl amine (yellow oil)

Reaction of nitrous acid with $3^{\circ}$ amines

Aliphatic $3^{\circ}$ amines on reaction with HONO form soluble nitrite salts, while aromatic $3^{\circ}$ amines form green coloured $p$ -nitroso amines.

$R_{3} N + HONO \longrightarrow \underset{\left(\text{Soluble nitrite} \right)}{\left[ R _{3} \overset{+}{N}H \right] NO _{2}^{-}}$

$Ph - NMe _{2}+ HONO \longrightarrow $