The manufacture of hydroquinone from the oxidation of p-diiso-propylbenxne is similar. However, in contrast to resorcinol, hydroquinonc has been produced successfully by Signal Chemical in the USA in a 2700 tonne-per-ycar plant sincc 1971 using a modified Hock process. Goodyear took over this hydroquinone production and currently produces a technical gradc material (95%). Mitsui Petrochcmical also started production of hydroquinone using a similar process in a 5000 tonne-pcr-year plant in Japan in 1975.

As in the USA and Europe, in Japan most hydroquinone is still produced by reducing p-quinone with iron at 50-80 °C. Thc p-quinone fccd is obtained from anilinc through a complex reaction involving oxidation with MnO₂ or CrO₃ in a solution acidified with H₂SO₄:

The process is burdened by considerable formation of manganese, chromium and iron salts, and ammonium sulfate. For this reason, all hydroquinone processes based on aniline in Japan have been shut down. and thc last US plant (Eastman Kodak) was converted from aniline to the Hock process in 1986. A 4000 tonne-per-year plant is still in operation in China.

Another process (Rhône-Poulenc) involves the oxidation of phenol with perfomic acid, or mixtures of H₂O₂ with carboxylic acids or mineral acids such as H₃PO₄ or HClO₄, at 90°C and with a low phenol conversion (< 10%). Pyrocatechol, the coupled product formed along with hydroquinone, has only a small market. Depending on reaction conditions, the hydroquinone/pyrocatechol ratio varies from about 60 : 40 to 40 : 60. The selectivity to both hydroxyphenols is 85-90% (based on H₂O₂). Rhbne-Poulenc operates a plant with a capacity of 18 000 tonncs per year ( 12 000 tonnes per year hydroquinone). A similar process, the oxidation of phenol with H₂O₂ developed by Ube Industries. is used commercially in Japan.

In Italy, Rrichima runs a process for the oxidation of phenol with H₂O, in a 5000 tonne-per-year plant. In the presencc of small amounts of iron- and cobalt-salt initiators, phenol is oxidized with 60% H₂O₂ at 40 °C in a radical reaction. The ratio of hydroquinone to pyrocatechol is between 40 : 60 and 20 : 80, with a total selectivity of over 90% and a phenol conversion of about 20%.

An older Reppe hydroquinone synthesis involving the ring-forming carbonylation of acetylene with Fe or Co complexes has been revised in various ways, with an emphasis on catalyst modification:

Du Pont uses Ru and Rh catalysts at 600-900 bar in thc presence of H₂ instead of H₂O. Ajinomoto and Lonza USC Rh and Ru(CO)₄ catalysts, rcspectivcly, at 100-300°C and 100-350 bar. Lonza (now Alusuisse-Konzern) operated a small pilot plant for several years, but no industrial plant has been constructed. The quantitative recovery of expensive noble metal catalysts was - as is usual in homogeneously catalyzed reactions - a very important but obviously unsolved problem.