Hydroquinone, Resorcinol, and Catechol

AbstractWorldwide manufacturing capacities of hydroquinone, resorcinol, and catechol are 50,000, 30,000, and 25,000 t/y, respectively. Selective processes leading to hydroquinone are achieved by the oxidation of aniline using manganese dioxide or the hydroperoxidation ofpara‐diisopropylbenzene. Selective resorcinol synthesis use alkali fusion of them‐benzenedisulfonic acid and the hydroperoxidation ofm‐diisopropylbenzene. Coproduction of hydroquinone and catechol is based on phenol hydroxylation by hydrogen peroxide. Much research has been devoted to the hydroxylation of phenol by hydrogen peroxide, in order to try to better master the ratio hydroquinone–catechol. In homogeneous catalysis, it has been found that it is possible to favor the formation of hydroquinone using benzaldehydes or benzophenones in conjunction with a strong acid. In the field of heterogeneous catalysis, the discovery of titanium silicalite (a synthetic molecular sieve) allowed phenol conversion up to 20%. In this case, solvent effects can favor the formation of hydroquinone. Numerous syntheses of hydroquinone, resorcinol, and catechol derivatives have been described.