At which of the following temperatures is the diazotisation of aniline best carried out?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 0°C
0 °C is 273 K, which lies in the range 273-278 K (0-5 °C) at which aniline is converted to benzenediazonium chloride. The arenediazonium salt is stable only for a short time at these low temperatures, so the reaction is kept ice-cold.
\( \displaystyle \ce{C6H5NH2 + NaNO2 + 2HCl} \xrightarrow{273-278\ \mathrm{K}} \ce{C6H5N2^+Cl^- + NaCl + 2H2O} \)
NCERT (2026-27 edition):
9.6 Chemical Reactions – “(b) Aromatic amines react with nitrous acid at low temperatures (273-278 K) to form diazonium salts, a very important class of compounds used for synthesis of a variety of aromatic compounds discussed in Section 9.7.”
II. DIAZONIUM SALTS – “… Primary aromatic amines form arenediazonium salts which are stable for a short time in solution at low temperatures (273-278 K).”