Hydroquinone-Benzoquinone

Neither the mechanism by which benzene damages bone marrow nor its role in the leukemia process are well understood. It is generally beheved that the toxic factor(s) is a metaboHte of benzene (107). Benzene is oxidized in the fiver to phenol [108-95-2] as the primary metabolite with hydroquinone [123-31-9] catechol [120-80-9] muconic acid [505-70-4] and 1,2,4-trihydroxybenzene [533-73-3] as significant secondary metabolites (108). Although the identity of the actual toxic metabolite or combination of metabolites responsible for the hematological abnormalities is not known, evidence suggests that benzene oxide, hydroquinone, benzoquinone, or muconic acid derivatives are possibly the ultimate carcinogenic species (96,103,107—112). 

In this reaction, the redox couple hydroquinone/benzoquinone promotes the second redox couple Pd(0), Pd(II) and Pd(II) causes the oxidative transformation of the diene to the 1,4-diacetoxylated compound. The most remarkable characteristic of this reaction... 

Benzoquine, see p-Quinone Benzoquinol, see Hydroquinone Benzoquinone, see p-Quinone Benzo-l,4-quinone, seep-Quinone... 

This was also confirmed by HPLC analysis which showed that only very small amounts of intermediates were originated (hydroquinone, benzoquinone, maleic and oxalic acids). 

Analysis for Phenol, Hydroquinone, Benzoquinone, and Catechol Phenol, hy-droquinone, benzoquinone and catechol can be detected with the d)C18 column (ID = 3.91mm, length = 50mm) and a UV detector at working wavelength of 190-400nm. Methanol/water (1/1, V/V) can be selected as the mobile phase at a flow rate of 0.5 mL min-1. /10.2 un membrane filter is necessary before injection. 

Absence of nitro derivatives was also observed upon irradiation of nitro-phenols and nitrate. Also in this case, the electron-withdrawing character of the nitro group can account for the inhibition of nitration [109]. The difficulty to nitrate nitrophenols to dinitrophenols is widely recognised [125] and also constitutes a problem in environmental chemistry, since field data seem, in contrast, to indicate that the nitration of 2-nitrophenol to 2,4-dinitrophenol in the atmospheric aqueous phase (e.g. cloud water) is an important process [126]. In fact, aqueous-phase nitration might be a relevant sink for 2-nitrophenol and possibly the main source of the dinitro compound, which is a powerful phytotoxic agent [127,128]. In the presence of nitrate under irradiation the main transformation intermediates of nitrophenols are the hydroxyl derivatives, while other compounds may derive from the direct photolysis of the substrates (catechol and 2-nitrosophenol from 2-nitrophenol hydroquinone, benzoquinone, hydroxybenzoquinone and 4-nitrosophenol from 4-nitrophenol) [109]. 

Mills et al. performed extensive investigations into the photocatalytic degradation of 4-chlorophenol. These included studies on the effects of different titania samples [102], effects of annealing temperature on the photocatalytic efficiency of titania [ 103] and a mechanistic study of the decomposition process. The rate of chlorophenol destruction was found to drop when using titania photo catalysts that had been heated above 600 °C. This was believed to be due to a build up of the rutile phase and a reduction of surface area following heat treatment above these temperatures. A number of intermediates were reported including 4-chlorocatechol, hydroquinone, benzoquinone and 4-chlororesorcinol [104],... 

The photocatalytic destruction of the fungicide 2-phenylphenol generated a range of by-products including hydroquinones, benzoquinones and dihy-droxybiphenyls [132]. This indicated that the major routes of degradation included hydroxylation and scission of the phenyl-phenol ring. The rate of... 

The use of renewable feedstocks for creating alternative synthetic routes to chemicals of major industrial importance is exemplified by the biosynthetic method for producing hydroquinone, benzoquinone, catechol, and ci.v-ci.v-muconic acid from glucose by means of a genetically altered... 

The migration principle was suggested as the reason of the enhancement of the antioxidant activity of polyester-polyether elastomer-bound hindered phenol by the addition of 0.25% of an easier migrating AO, 4,4 -bis(a,a-dimethylbenzyl)di-phenylamine (5) [181] this easier migrating amine is regenerated by the immobilized phenolic moiety, by means of the principle of homosynergism [5]. Similarly, a blend of polymeric redox hydroquinone-benzoquinone AO with equal amounts of iV-phenyl-iV -(l,3-dimethylbutyl)-l,4-phenylenediamine exerted a pronounced increase of antioxidant efficiency in SBR [124]. A synergistic combination based... 

The oxidation of phenol on a platinum anode was studied by the same author [34]. At a current density of 50mA/cm, 70°C, and a pH of 3, the initial phenol concentration of 21 mmol/dm completely disappeared in 2 h. Apart from CO2, other organic intermediates such as hydroquinone, benzoquinone, maleic acid, fumaric acid, and oxalic acid were identified. An analysis of the reaction intermediates and a carbon balance showed that the destruction reaction occurred by two parallel pathways chemical oxidation with electrogenerated hydroxyl radicals, and direct oxidation of phenol and/or its aromatic intermediates to CO2. 

In order to overcome the bubble formation associated with the sheathless CE-MS interface and quick degradation of the coated capillary, Moini et al. [9] introduced hydroquinone (HQ) as a buffer additive to suppress the bubbles formed due to the electrochemical oxidation of the CE buffer at the outlet electrode. The oxidation of water (2H2O (1) O2 (g) + 4H + 4c) was replaced with that of more easily oxidized HQ (hydroquinone / -benzoquinone + 2H + 2c). Formation of / -benzoquinone, other than... 

The direct oxidation of benzene to phenol is usually affected by a poor selectivity due to the lack of kinetic control. Indeed, phenol is more reactive towards oxidation than benzene itself and consecutive reactions occur, with substantial formation of overoxidized products like catechol, hydroquinone, benzoquinones and tars. This is the usual output of the oxidation of aromatic hydrocarbons by the classical Fenton system, a mixture of hydrogen peroxide and an iron(II) salt, usually ferrous sulfate, most often used in stoichiometric amounts [8]. 

AFP = a-fetoprotein HCG = human chorionic gonadotrophine IgG = immunoglobulin G HBs = hepatitis B surface antigen H2Q/BQ = hydroquinone/benzoquinone... 

Formaldehyde and formic acid are the two primary intermediates formed during the conversion of EG to CO2. Phenol, hydroquinone, benzoquinone, and benzoquinone epoxide arc a few of the intermediates formed during the initial stage of BZ oxidation. EG has been used as a surrogate waste in detailed investigations of the MEO process [13] since studies of its partial oxidation by Ag(n) had been previously published [22-24], BZ has been studied [ 13] since it will be aprimary constituent of mixed waste generated by the DWPF [17]. 

BZ was al so partially oxidized by Ag(II) in a small H-cell with stationary platinum electrodes. Compounds identified in anolyte extracts included phenol, hydroquinone, benzoquinone, benzaldehyde, benzoic acid, methyl benzoate, benzonitrile, benzonitrile aldehyde, and 4-nitro butylnitrile. The yellow color of the anolyte was probably due to benzoquinone, which had a relatively high concentration. A compound which was tentatively identified as benzoquinone epoxide ( 11403) was present at the highest concentration and is believed to be a product of the oxidation of benzoquinone. Numerous nitrated aromatics were also detected and include nitrobenzene, dinitrobenzene isomers, nitrophenol isomers, and dinitnophenol isomers. Intermediates are summarized in Table 3 and classified as I. BZ substrate II. nitrated BZs HI. phenols, quinones, and epoxides IV. nitrated phenols V. BZ substituted with aliphatic and aromatic... 

At around the time of maximum catechol and hydroquinone, benzoquinone began to appear and went thorough maximum. The disappearance of benzoquinone was then followed by the formation of maleic acid and fiimaric acid. These acids were then transformed into the lower molecular weight carboxylic acids such as glycolic acid, acetic acid, formic acid and oxalic acid. On the b2isis the sequence in which the reaction intermediates were formed reaction pathways of phenol oxidation could be proposed as the sequential steps in Figure 10. 

In connection with a study of a number of anticancer compounds which, presumably also act as inhibitors of free-radical polymerization, eight classes of compounds were studied as to their inhibitory properties. The classes studied were unsaturated hydrocarbons, phenolic compounds, quinones, amines, stable free-radicals, sulfiir compounds, carbonyl compounds, and metallic salts. The most effective inhibitors, of those evaluated, were cupric acetate and cupric resinate, followed by /runs-1,3,5-hexatriene, hydroquinone, benzoquinone, and diphenylamine as modest inhibitors. Among the low-activity inhibitors were 2,2-diphenyl-1-picrylhydrazyl, benzene thiol, and crotonaldehyde [70]. 

In studies of electrochemical photocurrents obtained at molecular semiconductor thin films (PcZn, (CN)sPcZn, TPyTAPZn, MePTCDI) and their dependence on the concentration of the reactant in the electrolyte (O2, ethylthiolate (RS ), hydroquinone/benzoquinone (HQ/BQ), Fe(CN)g, a sat-... 

Scheme 15.2 Square scheme showing all the possible pathways for the hydroquinone/ benzoquinone redox couple...

---