Which type of amine produces \( N_2 \) when treated with HONO?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Primary amine
Nitrous acid, \( \ce{HNO2} \) (made in the flask from \( \ce{NaNO2} \) and a mineral acid), reacts differently with the three classes of amines. A primary aliphatic amine forms an aliphatic diazonium salt, which is unstable and breaks down at once, giving an alcohol and nitrogen gas:
\( \displaystyle \ce{R-NH2 + HNO2} \xrightarrow{\ce{NaNO2 + HCl}} \ce{[R-N2+]Cl^-} \xrightarrow{\ce{H2O}} \ce{R-OH + N2 ^ + HCl} \)
(Primary aromatic amines give stable diazonium salts at 273–278 K, which release nitrogen only on warming.)
Why the other options are incorrect
Option (2) Secondary amine — Incorrect. Secondary amines have only one N–H hydrogen; they give yellow oily N-nitrosoamines, \( \ce{R2N-N=O} \), with no nitrogen gas.
Option (3) Tertiary amine — Incorrect. Aliphatic tertiary amines have no N–H hydrogen; they only form soluble nitrite salts.
Option (4) Quaternary ammonium salt — Incorrect. In \( \ce{R4N+} \) the nitrogen has no lone pair and no hydrogen, so it does not react with nitrous acid.
NCERT (2026-27 edition):
Reaction with Nitrous Acid
