Question

What is the product of the reaction of nitrous acid with aliphatic primary amine in the cold?
(A) A diazonium salt
(B) An alcohol
(C) A nitrite
(D) A dye

Answer 1

Hint: Amines are the compounds that contain an $N{{H}_{2}}$functional group in their structure. These are basic in nature as they contain nitrogen with a lone pair of electrons. These compounds are sensitive to pyrolysis when the $N{{H}_{2}}$ group is present.

Complete Step by Step Solution:
Reaction of $HN{{O}_{2}}$ with aliphatic amines, also known as the nitrous acid test, is an important test for distinguishing primary, secondary, and tertiary amines. When nitrous acid $HN{{O}_{2}}$ ) reacts with aliphatic primary amine in the cold, it first processes a diazonium salt, which is unstable. The diazonium salt then decomposes to alcohol along with the evolution of nitrogen gas (${{N}_{2}}$ ) and water.

Correct option: (B) An alcohol.

Additional information: At room temperature, primary amines are liquid, whereas secondary and tertiary amines are solid. Treatment of nitrous acid ($HN{{O}_{2}}$ ) with secondary amines gives an insoluble oil layer of nitrosamine; with tertiary amines, it gives a clear solution of quaternary ammonium salts.

Note: The nitrous acid test is used as a test for amines in organic chemistry to identify whether the compound has an amino functional group present or not. The primary amine can further be identified with the carbylamine test, in which amines are treated with chloroform in the presence of alkali. An alkyl isocyanide ($RNC$ ) is formed in this process. Both aliphatic and aromatic amines can give this test.