i) From aryl sulphonic acids
An aryl sulphonic acid yields the corresponding phenol on heating it with molten sodium hydroxide at 570 - 620 K. The sodium salt is obtained which is hydrolysed with acid to obtain free phenol.
ii) From haloarenes
Chlorobenzene (an haloarene) is hydrolysed by treating it with 10% NaOH at 623 K and 320 atmospheric pressure in presence of Cu catalyst. Phenol is obtained by acidification of sodium phenoxide.
iii) Hydrolysis of diazonium salts
A diazonium salt is formed by treating an aromatic primary amine with nitrous acid (obtained from a mixture of NaNO2 and HCl) at low temperature of 273 K to 278 K.
Diazonium salts are hydrolysed to phenols treating with dilute acids.