Ethanamine is treated with sodium nitrite and dilute hydrochloric acid at a low temperature. Which of the following is the result of this reaction?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Ethanol is formed, with evolution of nitrogen gas
Sodium nitrite and hydrochloric acid give nitrous acid in the reaction mixture. A primary aliphatic amine such as ethanamine forms an aliphatic diazonium salt with it. This salt is unstable: it breaks down at once, giving off nitrogen gas and leaving an alcohol.
\( \displaystyle \ce{C2H5NH2 + NaNO2 + 2HCl -> [C2H5N2^+Cl^-] + NaCl + 2H2O} \)
\( \displaystyle \ce{[C2H5N2^+Cl^-] + H2O -> C2H5OH + N2 ^ + HCl} \)
The nitrogen is given off quantitatively, which is why this reaction is used to estimate amino acids and proteins.
Why the other options are incorrect
Option (1) A stable ethanediazonium chloride is obtained, which can be kept at 273–278 K — Incorrect. Only aromatic amines give diazonium salts that can be used at 273–278 K. The aliphatic diazonium salt from ethanamine is unstable and decomposes.
Option (3) N-Ethylethanamide is formed — Incorrect. N-Ethylethanamide is the product of acylation, when ethanamine reacts with an acid chloride or anhydride such as ethanoyl chloride; nitrous acid does not do this.
Option (4) Ethanenitrile is formed — Incorrect. Nitriles and amines are linked the other way round: reduction of a nitrile gives a primary amine. Nitrous acid does not turn an amine into a nitrile.
NCERT (2026-27 edition):
9.6 Chemical Reactions – “Three classes of amines react differently with nitrous acid which is prepared in situ from a mineral acid and sodium nitrite.”
“(a) Primary aliphatic amines react with nitrous acid to form aliphatic diazonium salts which being unstable, liberate nitrogen gas quantitatively and alcohols. Quantitative evolution of nitrogen is used in estimation of amino acids and proteins.”