HYDROQUINONE, RESORCINOL, AND CATECHOL

Hydroquinone [123-31 -9] resorcinol [108-46-3] and catechol [120-80-9] (or pyrocatechol) are represented by structures (1), (2), and (3), respectively. This article reviews their syntheses and derivatives, production and use, and toxicology. 

During the 1980s few innovations were disclosed in the Hterature. The hydroxylation of phenol by hydrogen peroxide has been extensively studied in order to improve the catalytic system as well as to master the ratio of hydroquinone to catechol. Other routes, targeting a selective access to one of the dihydroxyben2enes, have appeared. World production capacities according to countries and process types are presented in Table 1. 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Comecon = Council for Mutual Economic Assistance (Communist-bloc nations). 

Aniline Oxidation. Even though this is quite an old process, it still has limited use to produce hydroquinone on a commercial scale. In the first step, aniline is oxidized by manganese dioxide in aqueous sulfuric acid. The resulting benzoquinone, isolated by vapor stripping, is reduced in a second step by either an aqueous acidic suspension of iron metal or by catalytic hydrogenation. 

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Hydroquinone [123-31 -9] represents a class of commercially important black-and-white chemical reducing agents (see Hydroquinone,RESORCINOL, AND catechol). The following scheme for silver haUde development with hydroquinone shows the quantitative importance of hydrogen ion and haUde ion concentrations on the two half-ceU reactions that describe the silver—hydroquinone redox system ... 

Polyhydric phenols with more than two hydroxy groups (ie, the three positional isomers of benzenetriol, the three isomeric benzenetetrols, benzenepentol [4270-96-6] and benzenehexol [608-80-0]) are discussed in this article. The benzenediols are catechol, resorcinol, and hydroquinone (see Hydroquinone, RESORCINOL, AND CATECHOL). 

The close electrochemical relationship of the simple quinones, (2) and (3), with hydroquinone (1,4-benzenediol) (4) and catechol (1,2-benzenediol) (5), respectively, has proven useful in ways extending beyond their offering an attractive synthetic route. Photographic developers and dye syntheses often involve (4) or its derivatives (10). Biochemists have found much interest in the interaction of mercaptans and amino acids with various compounds related to (3). The reversible redox couple formed in many such examples and the frequendy observed quinonoid chemistry make it difficult to avoid a discussion of the aromatic reduction products of quinones (see Hydroquinone, resorcinol, and catechol). 

Krumenacker, L., Costantini, M., Pontal, P. Sentenac. J. (1995) Hydroquinone, resorcinol, and catechol. In Kroschwitz, J.I. Howe-Grant. M.. eds, Kirk-Othmer Encyclopedia of Chemical Technology, 4th Ed., Vol. 13, New York. John Wiley, pp. 996-1014... 

HYDROQUINONE, RESORCINOL, AND CATECHOL] (Vol 13) 4,4y-Cyclohexylidenebis[N,N-bis(4-methylphenyl)]benzenamine(l,l-bis( di-4-tolyl-ammophenyl)cyclohexane) [58473-78-2]... 

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