Preparation of Phenol from Aniline

Aniline is diazotised with nitrous acid (generated in situ from NaNO2 + HCl) at the low temperature of 273-278 K (a diazonium salt decomposes above about 283 K) to give benzenediazonium chloride; warming this diazonium salt with hot water in the presence of a mineral acid hydrolyses it to phenol, releasing nitrogen gas: C6H5-NH2 with HNO2 at 273-278 K gives C6H5-N2+Cl-; then with H2O/heat gives C6H5-OH + N2 + HCl. This route is rarely used industrially (aniline itself is more valuable and more expensive to make than the phenol it would y …