Reaction of nitrous acid with aliphatic primary amine in cold gives.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → An alcohol
Primary aliphatic amines react with nitrous acid (\( \ce{NaNO2} \) + HCl) to give aliphatic diazonium salts. These are unstable even in the cold and at once lose nitrogen, giving an alcohol:
\( \displaystyle \ce{RNH2 + HNO2} \xrightarrow{\ce{NaNO2 + HCl}} \ce{[RN2+Cl-]} \xrightarrow{\ce{H2O}} \ce{ROH + N2 ^ + HCl} \)
The quantitative evolution of \( \ce{N2} \) is used to estimate amino acids and proteins.
Why the other options are incorrect
Option (1) A diazonium salt — Incorrect. Stable diazonium salts are formed only by aromatic primary amines at 273–278 K; the aliphatic ones decompose.
Option (3) A nitrite — Incorrect. The alkyl group ends up as an alcohol, not as a nitrite ester.
Option (4) A dye — Incorrect. Azo dyes come from aromatic diazonium salts coupled with phenols or amines.
NCERT (2026-27 edition):
Reaction with Nitrous Acid
