Hydroquinone and Catechol

The oxidation of these substances (H2Q = 1,4-dihydroxybenzene and H2Cat = 1,2-dihydroxybenzene) by Ni(III)(cyclam) yields the correspond- 

Ethylene glycol, 2,3-butanediol, and pinacol are oxidized by [IrCls] at measurable rates in acetic acid-sodium acetate solutions to formaldehyde, acetaldehyde, and acetone, respectively. Spectrophotometric evidence for prior complexation was obtained, and the protonation of the intermediate to an unreactive form invoked to explain the failure of the reaction to occur at higher acidities. The dependence of rate on diol concentration, and the observation that acrylamide is polymerized are cited as evidence to support the mechanism in equations (88) and (89)  

The oxidation of diols by V(V) is first order with respect to each reagent, and also occurs more rapidly in sulfuric than in perchloric acid, with a first-order dependence on Oxidations by Ce(IV) are also 

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Starting from Benzene. In the direct oxidation of benzene [71-43-2] to phenol, formation of hydroquinone and catechol is observed (64). Ways to favor the formation of dihydroxybenzenes have been explored, hence CuCl in aqueous sulfuric acid medium catalyzes the hydroxylation of benzene to phenol (24%) and hydroquinone (8%) (65). The same effect can also be observed with Cu(II)—Cu(0) as a catalytic system (66). Efforts are now directed toward the use of Pd° on a support and Cu in aqueous acid and in the presence of a reducing agent such as CO, H2, or ethylene (67). Aromatic... 

Hydroquinone and catechol are important industrial intermediates, and there has been significant research and development of processes for manufacturing their derivatives. 

Titanium Silicates. A number of titanium siUcate minerals are known (160) examples are Hsted in Table 19. In most cases, it is convenient to classify these on the basis of the connectivity of the SiO building blocks, eg, isolated tetrahedra, chains, and rings, that are typical of siUcates in general. In some cases, the SiO units may be replaced, even if only to a limited extent by TiO. For example, up to 6% of the SiO in the garnet schorlomite can be replaced by TiO. In general, replacement of SiO by TiO bull ding blocks increases the refractive indices of these minerals. Ti has also replaced Si in the framework of various zeofltes. In addition, the catalytic activity of both titanium-substituted ZSM-5 (TS-1) and ZSM-11 (TS-2) has received attention (161), eg, the selective oxidation of phenol, with hydrogen peroxide, to hydroquinone and catechol over TS-1 has been operated at the 10,000 t/yr scale in Italy (162). 

Because LCEC had its initial impact in neurochemical analysis, it is not, surprising that many of the early enzyme-linked electrochemical methods are of neurologically important enzymes. Many of the enzymes involved in catecholamine metabolism have been determined by electrochemical means. Phenylalanine hydroxylase activity has been determined by el trochemicaUy monitoring the conversion of tetrahydro-biopterin to dihydrobiopterin Another monooxygenase, tyrosine hydroxylase, has been determined by detecting the DOPA produced by the enzymatic reaction Formation of DOPA has also been monitored electrochemically to determine the activity of L-aromatic amino acid decarboxylase Other enzymes involved in catecholamine metabolism which have been determined electrochemically include dopamine-p-hydroxylase phenylethanolamine-N-methyltransferase and catechol-O-methyltransferase . Electrochemical detection of DOPA has also been used to determine the activity of y-glutamyltranspeptidase The cytochrome P-450 enzyme system has been studied by observing the conversion of benzene to phenol and subsequently to hydroquinone and catechol... 

Based on this technology, an industrial process for producing hydroquinone and catechol was developed by EniChem Synthesis starting at 10,000 tons per year (Fig. 6.3).36... 

Hydroquinones and catechols are oxidized efficiently and cheaply to the corresponding quinones, although it is important to adjust the acidity of the reaction mixture to pH 8, in order to avoid side reactions [6], Yields tend to be higher when chloroform is used as the solvent. 

Selected examples of quinones from hydroquinones and catechols... 

It has been suggested that phenol exposure results in cardiac effects because it blocks the cardiac sodium channel subtype, with little effect on sodium channels in skeletal muscle (Zamponi et al. 1994). Phenol does not appear to be carcinogenic following oral exposure (NCI 1980), although the chemical combinations that result from benzene and phenol metabolism may contain compounds that do initiate or promote cancer. Metabolites such as hydroquinone and catechol have been demonstrated to be genotoxic and clastogenic. 

Sawahata T, Neal RA. 1983. Biotransformation of phenol to hydroquinone and catechol by rat liver microsomes. Mol Pharmacol 23 453-460. 

The majority of systems studied have been aqueous solutions of either aromatic compounds or halogenated hydrocarbons. Such materials represent models for the major classes of organic pollutants in waste and ground water. The primary products resulting from the sonochemical treatment of phenol at 541 kHz (27 °C with bubbled air) are hydroquinone and catechol [22]. These compounds are easy to monitor and are clearly seen to be intermediates which disappear as the reaction progresses (Fig. 4.1). Similarly the sonolysis of aqueous 4-chlorophenol leads to products mainly characteristic of oxidation by OH radical e. g. 4-chlorocatechol but in both cases the final organic products are CO, CO2 and HCOOH (Scheme 4.2) [22-25]. 

Sud et al. (1972) discovered that a strain of Achromobacter sp. utilized carbaryl as the sole source of carbon in a salt medium. The organism grew on the degradation products 1-naphthol, hydroquinone, and catechol. 1-Naphthol, a metabolite of carbaryl in soil, was recalcitrant to degradation by a bacterium tentatively identified as an Arthrobacter sp. under anaerobic conditions (Ramanand et al., 1988a). Carbaryl or its metabolite 1-naphthol at normal and ten times the field application rate had no effect on the growth of Rhizobium sp. or Azotobacter chroococcum (Kale et al., 1989). The half-lives of carbaryl under flooded and nonflooded conditions were 13-14 and 23-28 d, respectively (Venkateswarlu et al., 1980). 

Like its monomeric counterpart, the polymeric reagent is inert to simple amines, amides, alcohols and phenols, but easily oxidizes thiols to disulphides, phosphines to phosphine oxides, hydroquinone and catechol to quinones, and thioketones, thioesters and trithiocar-bonates to the corresponding 0x0 derivatives, in dichloromethane, chloroform or acetic... 

The suggested mechanisms differ in detail (Mott, 66, 67 Berg, 68 Anastasevich, 69 Frank-Kamenetskii, 70 Bagdasar yan, 17, 71) but all involve the idea that electrons can be transferred to silver much more readily than to a silver halide crystal. Each mechanism can be criticized on some detail (cf. Sheppard, 15 James, 72). As a general criticism, however, none of the mechanisms has explained the fact that the rate of development under simplified conditions varies with the square root of the hydroquinone and catechol concentrations, whereas the rate of reduction of silver ions from solution by the same agents varies as the first or somewhat higher power of the concentration. 

The production of hydroquinone and catechol by TS-1 catalyzed hydroxylation of phenol with H2O2 appeared competitive with respect to existing industrial processes. A new industrial process has been developed based on TS-1 and a plant for the production of 10,000 tons/y of diphenols has been built in Ravenna, Italy [7], It operates since 1986 with excellent results. A plant for the industrial production of TS-1 has also been built to provide the diphenols plant with the required amount of catalyst. 

The discovery of titanium substituted ZSM-5 (TS-1) and ZSM-11 (TS-2) have led to remarkable progress in oxidation catalysis (1,2). These materials catalyze the oxidation of various organic substrates using aqueous hydrogen peroxide as oxidant. For example, TS-1 is now used commercially for the hydroxylation of phenol to hydroquinone and catechol (/). Additionally, TS-1 has also shown activity for the oxidation of alkanes at temperatures below 1()0 °C (3,4). 

The incorporation of vanadium(V) into the framework positions of silicalite-2 has been reported by Hari Prasad Rao and Ramaswamy469. With this heterogeneous oxidation catalyst the aromatic hydroxylation of benzene to phenol and to a mixture of hydroquinone and catechol could be promoted. A heterogeneous ZrS-1 catalyst, which has been prepared by incorporation of zirconium into a silicalite framework and which catalyzes the aromatic oxidation of benzene to phenol with hydrogen peroxide, is known as well in the literature. However, activity and selectivity were lower than observed with the analogous TS-1 catalyst. 

Ni(III) complexes oxidize some substrates. For example, [Ni(cy-clam)]3+ oxidizes hydroquinone and catechol in aqueous perchlorate media. The kinetics of the reactions have been studied (122). 

Leanderson, P. Tagesson, C. (1990) Cigarette smoke-induced DNA-damage role of hydroquinone and catechol in the formation of the oxidative DNA-adduct, 8-hydroxydeoxygua-nosine. Chem.-biol. Interact., 75, 71-81... 

Li, Q., Aubrey, M.T., Christian, T. Freed, B.M. (1997) Differential inhibition of DNA synthesis in human T cells by the cigarette tar components hydroquinone and catechol. Fundam. appl. Toxicol., 38, 158-165... 

Wallin, H., Melin, P, Schelin. C. Jergil. B. (1985) Evidence that covalent binding of metabolically activated phenol to microsomal proteins is caused by oxidised products of hydroquinone and catechol. Chem.-biol. Interact., 55. 335-346... 

Phenolic substances are for the most part readily oxidized at a graphite electrode. The oxidation potentials for phenols vary widely with structure, and some (hydroquinones and catechols) are far more readily oxidized than others (cresols). Many compounds of biological interest (catecholamines, pharmaceuticals, plant phenolics) [32] and industrial interest (antioxidants, antimicrobials, agricultural chemicals) [33] are phenolic, and trace determination based on LCEC is now quite popular. 

Glycol monomethyl ethers Monoepoxides Hydroquinone and catechol Phenol... 

The mechanism for the breakdown of phenol after hydroxylation of benzene can be seen in Figure 12.1. Several dihydroxy-substituted phenol derivatives were observed upon irradiation hydroquinone, catechol, and trace amounts of resorcinol (Nickelsen et al., 1993a,b). However, hydroquinone and catechol were both formed at the highest concentration at a low absorbed dose and their concentration decreased with increasing radiation to below detection limits at a dose of 300 krad. At a pH of 9 and a dose of 100 krad, dihydroxy-substituted phenol concentrations increased. When the pH was 5 and 7, the maximum concentrations of these products were found at 50 krads, suggesting a more efficient removal at a lower pH. 

Example, 2.1.3.1) with relatively large positive standard potentials. Dihydric phenols such as hydroquinone and catechol are moderately reducing substances that can be oxidized to the corresponding quinones (Example 2.1.2.2). For the case of PCE and catechol, the combination of these reactions gives ... 

Aromatic species which are activated for electrophilic substitution may be hydroxylated in the presence of strong acids. The largest single application of this technology is for the hydroxylation of phenol to hydroquinone and catechol using a mixture of perchloric and phosphoric acids as catalysts.468 As the products are more readily oxidized compared with the substrate, it is important to limit the conversion of the phenol to prevent over-oxidation to tars. 

Data produced in vitro by mouse and rat liver microsomes also indicate species differences in benzene metabolism (Schlosser et al. 1993). Quantitation of metabolites from the microsomal metabolism of benzene indicated that after 45 minutes, mouse liver microsomes from male B6C3Fj mice had converted 20% of the benzene to phenol, 31% to hydroquinone, and 2% to catechol. In contrast, rat liver microsomes from male Fischer 344 rats converted 23% to phenol, 8% to hydroquinone, and 0.5% to catechol. Mouse liver microsomes continued to produce hydroquinone and catechol for 90 minutes, whereas rat liver microsomes had ceased production of these metabolites by 90 minutes. Muconic acid production by mouse liver microsomes was <0.04 and <0.2% from phenol and benzene, respectively, after 90 minutes. 

Schoeters et al. (1995) evaluated the hematopoietic and osteogenic toxicity of benzene, phenol, hydroquinone, and catechol in vitro using murine bone marrow cultures. Evaluation of toxicity to 3T3-fibroblasts was included to determine specific toxicity to marrow cells. Benzene and phenol showed little effect. However, hydroquinone inhibited proliferation of 3T3 cells and marrow precursor cells, and calcification of bone cells, although it was more specific for marrow cells. Catechol inhibited all cells, and showed no specificity. 

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