When an aromatic primary amine is treated with nitrous (NaNO2+ HCl) acid at 273 – 278 K, diazonium salts are obtained. These diazonium salts are highly reactive in nature. Upon warming with water, these diazonium salts finally hydrolyze to phenols with the liberation of nitrogen gas. Phenols can also be obtained from diazonium salts by treating it with dilute acids.