Oxidation of hydroquinones

When a solution of, say, 1 g. of hydroquinone in 4 ml. of rectified spirit is poured into a solution of 1 g. of quinone in 30 ml. of water, qulnhydrone C,HA.C,H (0H)3, a complex of equimolecular amounts of the two components, is formed as dark green crystals having a gfistening metallic lustre, m.p. 172°. In solution, it is largely dissociated into quinone and hydroquinone. Quinhydrone is more conveniently prepared by the partial oxidation of hydroquinone with a solution of iron alum. 

In small-scale syntheses, a wide variety of oxidants have been employed in the preparation of quinones from phenols. Of these reagents, chromic acid, ferric ion, and silver oxide show outstanding usefulness in the oxidation of hydroquinones. Thallium (ITT) triduoroacetate converts 4-halo- or 4-/ f2 -butylphenols to l,4-ben2oquinones in high yield (110). For example, 2-bromo-3-methyl-5-/-butyl-l,4-ben2oquinone [25441-20-3] (107) has been made by this route. 

EFFECTS OF AMINES IN OXIDATION OF HYDROQUINONE WITH HYDROGEN PEROXIDE CATALYZED BY COPPER(H)... 

By the oxidation of hydroquinone in 60 per cent acetic acid with chromic acid. Craven and Duncan, J. Chem. Soc. 127, 1489 (1925). 

In a perchlorate medium the oxidation of hydroquinone to p-benzoquinone by chromic acid obeys the rate expression ... 

Oxidation of hydroquinone" by Mn(III) in acid perchlorate media is simple second-order. The acidity dependence indicates both Mn and MnOH to be effective oxidants with second-order rate coefficients at 25 °C of (0.48 + 0.12) x 10 ... 

The early work of Porret has been superseded by that of Baxendale et who found the oxidation of hydroquinone (QH2) by Fe(ril) perchlorate to follow the rate law... 

The organic substrates in Chart 8 can be divided into two main categories in which (i) the oxidation of olefins, sulfides, and selenides involves oxygen atom transfer to yield epoxides, sulfoxides, and selenoxides, respectively, whereas (ii) the oxidation of hydroquinones and quinone dioximes formally involves loss of two electrons and two protons to yield quinones and dinitrosobenzenes, respectively. In order to provide a unifying mechanistic theme for the seemingly disparate transformations in Chart 8, we note that nitrogen dioxide exists in equilibrium with its dimeric forms, namely, the predominant N—N bonded dimer 02N—N02 and the minor N—O bonded isomer ONO—N02 (equation 88). 

Quinone dyes, 9 503 Quinone ketals, anodic oxidation of hydroquinone ethers to, 21 264 Quinone methides, 2 209-211 Quinone Michael addition chemistry, 21 248-249, 250, 252 Quinone monoacetals, 21 251 Quinone monoimine (QMI), 19 246 Quinone oximes, formation of,... 

The 02-oxidation of hydroquinone into quinone, which is very slow in the absence of a catalyst, was found to be accelerated by the addition of the ce-pyrrolinonate-bridged Pt(2.5 + )4 (19) (117). The detailed kinetic investigation revealed that the Pt(2.0+)2 species formed according to Eq. (1) plays a major role as the catalyst. The reaction rate of the quinone formation is higher than that of 02 oxidation of Pt(2.0+)2 into Pt(3.0 + )2 and was found to be rather linear to the hydroquinone concentration. Therefore, it was suggested that the quinone formation proceeds via a certain intermediate formed between the Pt(2.0+)2 species and molecular oxygen (e.g., peroxo species). The possible schematic mechanism is illustrated in Eq. (12). 

Quinone may be prepared by the oxidation of aniline with dichromate or manganese dioxide and sulfuric acid.1 This is a more feasible commercial method than the one given. However, the oxidation of hydroquinone is more rapid and convenient and, hence is more desirable for use in the laboratory. Various materials have been oxidized by chemical means to give quinone they are quinic acid,2 hydroquinone,3 benzidine,4 -phenylene-diamine,5 sulfanilic acid,6 / -phenolsulfonic acid,7 arbutin,8 aniline black,9 and the leaves of various plants.10 Quinone is also formed by several other methods by the fermentation of fresh grass 11 by the action of iodine on the lead salt of hydroquin-... 

It is well to note at this point that the dihydroxy compound is the first identifiable compound from the photolysis and photo-oxidation reactions that actually has any color. The lack of other identifiable color compounds and also some preliminary experiments lead to a proposal [9] that the oxidation of the dihydroxy compound could actually continue on to give a quinone (Scheme 18.5, top). Given the ease of oxidation of hydroquinone compounds, this would seem to be a reasonable proposal. In this preliminary report where an orange-red solid was initially observed it was speculated that the color owed itself to a quinone compound as shown. This would add significantly to compounds that actually could be the color bodies formed upon weathering exposure. 

Selenium-hydrogen peroxide oxidation of hydroquinones (Table 10.32)... 

Chemical/Physical. Ozonolysis products reported are p-quinone and dibasic acids (Verschueren, 1983). Moussavi (1979) studied the autoxidation of hydroquinone in slightly alkaline (pH 7 to 9) aqueous solutions at room temperature. The oxidation of hydroquinone by oxygen followed first-order kinetics that yielded hydrogen peroxide and / -quinone as products. At pH values of 7.0, 8.0, and 9.0, the calculated half-lives of this reaction were 111, 41, and 0.84 h, respectively (Moussavi, 1979). 

Electron-transfer chains in plants differ in several striking aspects from their mammalian counterparts. Plant mitochondria are well known to contain alternative oxidase that couples oxidation of hydroquinones (e.g., ubiquinol) directly to reduction of oxygen. Semiquinones (anion-radicals) and superoxide ions are formed in such reactions. The alternative oxidase thus provides a bypass to the conventional cytochrome electron-transfer pathway and allows plants to respire in the presence of compounds such as cyanides and carbon monoxide. There are a number of studies on this problem (e.g., see Affourtit et al. 2000, references therein). 

MPa O2). The role of the encapsulated [Co(salophen)] complexes is to catalyze the aerobic oxidation of hydroquinone to p-benzoquinone, which in turn oxidizes Pd(0). For the oxidation of 1,3-cyclohexadiene to l,4-diacetoxy-2-cyclohexene, the most active catalyst system involved the encapsulated complex [Co(tetra-tert-butyl-salophen)], which afforded product yields of 85-95% after 3 h at room temperature with greater than 90% trans-selectivity. This complex displayed significantly higher activity than the encapsulated [Co(salophen)] complex (72% yield in 3h) and the analogous homogeneous complex (86% yield in 5h). The increased activity of the t-butyl substituted catalyst was attributed to distortion of the bulky complex by the... 

Subsequently, Backvall and coworkers developed triple-catalysis systems to enable the use of dioxygen as the stoichiometric oxidant (Scheme 3) [30-32]. Macrocyclic metal complexes (Chart 1) serve as cocatalysts to mediate the dioxygen-coupled oxidation of hydroquinone. Polyoxometallates have also been used as cocatalysts [33]. The researchers propose that the cocatalyst/BQ systems are effective because certain thermodynamically favored redox reactions between reagents in solution (including the reaction of Pd° with O2) possess high kinetic barriers, and the cocatalytic mixture exhibits highly selective kinetic control for the redox couples shown in Scheme 3 [27]. 

The oxidation of hydroquinones with molecular oxygen is possible only in the presence of a catalyst, i.e. activated carbon. The velocity of oxidation decreases with increasing redox potential 13>14> (Duroquinone is formed more quickly than chloranil). For this reason, particularly with chelates that have a rather high redox potential, it cannot be assumed that oxidation in accordance with Reaction (9) proceeds with sufficient velocity. 

Electrochemical oxidation of hydroquinone was investigated on a rotating disk electrode in a solution containing 0.01 M quinone and hydroquinone in 0.5 M H2so4 at 298 K. The following values of current density at different electrode potential values and RDE rotation rates were obtained ... 

Figure 4.65 Oxidation of hydroquinone to quinone and multiple conjugation with glutathione. Biliary excretion of the conjugate and reabsorption allow further metabolism (phase 3) in the gut and kidney to the cysteine conjugate, which is nephrotoxic.

Li, Y. Trush, M. A. (1993 a) DNA damage resulting from the oxidation of hydroquinone by copper role for a Cu(II)/Cu(I) redox cycle and reactive oxygen generation. Carcinogenesis, 14, 1303-1311... 

Li, Y. Tmsh, M.A. (1993b) Oxidation of hydroquinone by copper chemical mechanism and biological effects. Arch. Biochem. Biophys., 300, 346-355... 

Schlosser, M.J., Shurina, R.D. Kalf, EG (1990) Prostaglandin H synthase catalyzed oxidation of hydroquinone to a sulfhydryl-binding and DNA-damaging metabolite. Chem. Res. Toxicol., 3, 333-339... 

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