Process for the hydroxylation of phenol

A process for preparing pyrocatechol and hydroquinone, wherein phenol is reacted at the start of the reaction with substantially anhydrous hydrogen peroxide obtained by distilling off hydrogen peroxide which is in the form of non-aqueous solution whose solvent boils at a higher temperature than the phenol, together with the phenol from the higher boiling solvent, and reacting, before or after condensation, the vapors containing hydrogen peroxide which distill over, optionally following the addition of a stabilizer, wherein the reaction is carried out in the presence of a strong acid selected from the group consisting of sulfuric acid, perchloric acid, nitric acid, trifluoromethanesulfonic acid, perfluorobutanesulfonic acid, a fluorinated acid ion exchanger of a sulfonated polymeric fluorine-substituted hydrocarbon and fluorosulfonic acid at a temperature of 20.degree.-150.degree. C and recovering pyrocatechol and hydroquinone.