For diazonium salts, select the incorrect statement.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Benzene diazonium salts on reaction with ethanol produce N2O.
Arenediazonium salts (\( \ce{ArN2^{+}X^{-}} \)) are stabilised by resonance of the –\( \ce{N2^{+}} \) group with the benzene ring. They are stable in cold solution (273–278 K), but the –\( \ce{N2^{+}} \) group is an excellent leaving group: it is replaced by other groups with the loss of nitrogen gas (N2).
With ethanol (a mild reducing agent), the diazonium group is replaced by hydrogen. Ethanol is oxidised to ethanal:
\( \displaystyle \ce{C6H5N2^+Cl^- + CH3CH2OH -> C6H6 + N2 + CH3CHO + HCl} \)
Option (1) Aliphatic diazonium salts are unstable in nature. — A correct statement about diazonium salts. Without a ring to delocalise the charge, they decompose at once, giving \( \ce{N2} \) and a mixture of products.
Option (2) Aromatic diazonium salts are not unstable comparatively. — A correct statement about diazonium salts. Resonance with the ring makes them stable enough to be used in cold solution soon after preparation.
Option (3) Benzene diazonium salt on reaction with water at 283 K, produces phenol. — A correct statement about diazonium salts. If the temperature of the solution rises to about 283 K, the salt is hydrolysed to phenol: \( \ce{C6H5N2^+Cl^- + H2O -> C6H5OH + N2 + HCl} \)
Option (4) Benzene diazonium salts on reaction with ethanol produce N2O. — The incorrect statement. The gas given off is N2, not \( \ce{N2O} \), and the organic product is benzene.
NCERT (2026-27 edition):
Diazonium Salts – “… Primary aliphatic amines form highly unstable alkyldiazonium salts (refer to Section 9.6). Primary aromatic amines form arenediazonium salts which are stable for a short time in solution at low temperatures (273-278 K). The stability of arenediazonium ion is explained on the basis of resonance.”
Replacement by Hydroxyl Group – “If the temperature of the diazonium salt solution is allowed to rise upto 283 K, the salt gets hydrolysed to phenol.”
Replacement by H
