32.2.1—Preparation of phenol

Phenylamine is converted to a diazonium salt with nitrous acid (or sodium nitrite plus dilute acid) below 10 °C. Warming the diazonium salt with water replaces the diazonium group by –OH to give phenol.

The low temperature stabilises the diazonium salt during preparation; warming is used for the subsequent hydrolysis step. Treat the two stages as separate conditions.

C₆H₅NH₂ → diazonium salt below 10 °C, then aqueous warming → C₆H₅OH. Nitrogen gas is released when the diazonium group leaves.

Do not warm the phenylamine/nitrite mixture during diazotisation or skip the diazonium intermediate in the syllabus route.