Question

If the reaction of $HN{{O}_{2}}$ with ‘A’ gives quaternary ammonium salt, then what is compound "A"?
(A) Methyl amine
(B) Dimethyl amine
(C) Trimethylamine
(D) Aniline

Answer 1

Hint: Quaternary ammonium salt is an organic compound in which the ammonia molecule is tetra substituted with alkyl or aryl groups and has a cationic state. They are used as surfactants, electrolytes, ionic liquids, alkylating agents, phase transfer catalysts, deprotecting agents, and other materials. Examples of quaternary ammonium salts are cetylpyridinium chloride, cetylpyridinium bromide, benzethonium chloride, etc.

Complete Step by Step Solution:
Reaction of $HN{{O}_{2}}$ with aliphatic amines is an important test for distinguishing primary, secondary, and tertiary amines. On treatment of primary amine with nitrous acid ($HN{{O}_{2}}$), nitrogen gas is released, which can be seen as bubbles. Treatment of nitrous acid ($HN{{O}_{2}}$) with secondary amines gives an insoluble oil layer of nitrosamine.

Quaternary ammonium salts with a clear solution are formed only when a tertiary amine reacts with nitrous acid. In this case, nitrous acid ($HN{{O}_{2}}$) reacts with trimethyl amine to give quaternary ammonium salts. Hence, the compound ‘A’ is trimethylamine.
Correct option (C) Trimethylamine.

Additional Information: The quaternary ammonium salt produced by the reaction of nitrous acid with tertiary amine can decompose further to produce nitrosamines and alcohol.

Note: As methyl amine is a primary amine, aniline is a primary aromatic amine, and dimethyl amine is a secondary amine, so these compounds do not give quaternary salts on reaction with nitrous acid ($HN{{O}_{2}}$).