Hydroquinone and Derivatives

Hydroquinone and the monobenzyl ether of hydroquinone are used as depigment-ing agents in bleach creams and skin lighteners. The latter is a well-known sensitizer, also used in the rubber industry. Fisher (1973, p. 235) found 5% of users allergic to this compound. 

Hydroquinone appears to be less of a sensitizer, but erythema, progressing to post inflammatory hyperpigmentation, occurred among the most frequently encountered adverse effects in a trial comprising 840 South African volunteers (Bent- 

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A regular decrease in the half-wave potentials for the hydroquinone series is caused by the substituents in position 2 its shift bears a linear relationship to the substituent steric constants (20). It is apparent from the relationship of the logarithm of relative activity to the half-wave potentials E0 (Figures 2 and 3) that the relationship in the entire series of the derivatives is not linear. The activity declines with the half-wave potentials in comparison with hydroquinone and derivatives substituted by methyl, ethyl, and isopropyl groups with derivatives substituted by tertiary alkyl groups, however, a reverse relationship was found, as was... 

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. 

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

Conversion of Aromatic Rings to Nonaromatic Cyclic Structures. On treatment with oxidants such as chlorine, hypochlorite anion, chlorine dioxide, oxygen, hydrogen peroxide, and peroxy acids, the aromatic nuclei in lignin typically ate converted to o- and -quinoid stmctures and oxinane derivatives of quinols. Because of thein relatively high reactivity, these stmctures often appear as transient intermediates rather than as end products. Further reactions of the intermediates lead to the formation of catechol, hydroquinone, and mono- and dicarboxyhc acids. 

HPLC method with amperometric detection was applied for detenuination of phenols in sea sediment and some dmg preparation. Peaks of phenol, guaiacol, cresols, hydroquinon and resorcinol were identified on chromatogram of birch tai. The HPLC method with electrochemical detectors was used for detenuination of some drug prepai ation of aminophenol derivate. So p-acetaminophenol (paracetamol) was determined in some drug. 

Fluorescein paraffin derivatives, waxes, hydrocarbons [140,141] aliphatic acids [142] hydroquinone and chlorinated derivatives [143] isoprenoids, quinones [111,144] oxathizine fungicides [145] barbiturates, phenothiazines [146]... 

Because of the strongly electron-withdrawing character of the Cr(CO)5 unit, the reaction with alkynes to hydroquinone and phenol derivatives [35-37] (Dotz reaction) is possible according to Scheme 6 (see also Chap. 4 Chromium -templated Benzannulation Reactions ). 

The effects of pH on electrokinetic velocities in micellar electrokinetic chromatography was studied by using sodium dodecyl sulfate solutions [179]. Micellar electrokinetic capillary chromatography with a sodium dodecyl sulfate pseudostationary phase has been used to determine the partition constants for nitrophenols, thiazolylazo dyes, and metal chelate compounds [180]. A similar technique was used to separate hydroquinone and some of its ether derivatives. This analysis is suitable for the determination of hydroquinone in skin-toning creams [181]. The ingredients of antipyretic analgesic preparations have also been determined by this technique [182], The addition of sodium dodecyl sulfate improves the peak shapes and resolution in chiral separations by micellar electrokinetic chromatography [183]. 

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 thermally unstable acethylenic thiols 142, which are produced from the corresponding halogen substituted acetylene derivatives 141, have been reported to undergo, in the presence of hydroquinone and nitrogen at — 15°C, heterocyclization to the derivatives 143, 144, and 145 (Eq. 22). ... 

Bicyclic bridged phosphorinane derivatives can be synthesized by different methods. When phenylphosphine is heated with cycloocta-2,7-dienone to 135 °C in the presence of polymerization inhibitors, e.g. hydroquinone, and the double Michael addition product is oxidized, the two crystalline syn and anti isomers (total yield 48-59%) are isolated. Separation by crystallization gives the pure compounds which can in turn be transformed at the carbonyl or the phosphorus group (equation 10) (75T33,76JOC589). 

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. 

Diacyloxyiodo)benzenes like 3 and 4 have been especially popular for the oxidation of phenol derivatives. Recently some electronically modified reagents of this type have been synthesized, where the benzene moiety has been replaced by a heteroaromatic system. For compounds 15-17 see Scheme 3. The reagents 15 and 16 have been used for oxidations of hydroquinones and sulfides as well... 

Well-established is the formation of hydroquinone and phenol derivatives 273 from alkynes. This reaction is called the Dotz reaction [78,79]. The reaction of carbene complex 271 to give 273 can be expressed by the general scheme 272. 

Rate constants for the reactions of S0o with a wide variety of organic compounds are summarized in Table 2. The sulfite radical was found to oxidize ascorbate, trolox (a water soluble tocopherol derivative), methoxyphenol, hydroquinone and other phenolic compounds, sulfonated hydroquinones, phenylenediamines, and phenothiazines with rate constants ranging to 1 CrM 1 s. ... 

In recent years hypervalent iodine compounds have experienced extensive investigations yielding many results of practical synthetic importance. Supported iodi-nanes, i.e. iodoso or iodine(III) reagents, have been prepared by several groups, mainly as the bis-acetoxyiodoso derivatives [15-18] or as the respective dihalogeno compounds [19]. Iodoso reagents are employed in the oxidation of hydroquinones and phenols that have been exploited in the formation of spiroketals from a variety of tyrosines. 

A hr dm 3. Recently, the electrochemical incineration of p-benzoquinone in acetate buffer has been reported by Houk et al. [54]. The cell was similar to that above cited for 4-chlorophenol oxidation (see Sec. III.B), with a Ti or Pt anode coated with a film of the oxides of Ti, Ru, Sn, and Sb. These anodes are stable but somewhat less efficient than an Fe(III)-doped Pb02 film coated on Ti employed in a previous work [55], The COD of 50 mL of 100 ppm / -benzoquinone decreased from an initial value of 190 to 2 ppm during 64 hr of electrolysis at 1 A. The major intermediate products identified were hydroquinone and aliphatic acids including maleic, succinic, malonic, and acetic acids. The suggested reaction sequence is given in Fig. 13, where succinic acid is obtained from a cathodic reduction of maleic acid, which is formed from the breakdown of the dihydroxylated derivative generated by an attack of adsorbed hydroxyl radicals onto p-benzoquinone. Further mineralization of succinic acid occurs via its consecutive oxidation to malonic and acetic acids. 

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