Benzene, biological oxidation

Benzene oxide and compounds derived from it are carcinogenic and can react with DNA to induce mutations This difference m the site of biological oxidation—ring versus side chain—seems to be responsible for the fact that benzene is carcinogenic but toluene is not... 

The biological oxidation of phenylalanine to tyrosine and its conversion to 3 4-dihydroxy derivatives is an established fact. The direct conversion of phenylalanine to tyrosine in the animal body has been demonstrated by Moss and Schoenhfflmer (7), by feeding phenylalanine with deuterium in the benzene ring. According to Bemheim and Bern-heim (8), this conversion can be regarded as a step in normal intermediary metabolism and is probably dependent upon a specific enzyme system. 

Benzene associated with the adsorbent pellet was determined by oxidizing the organic materials at 900 C in a stream of oxygen. For this work a Harvey Biological Oxidizer, model OX-100, was used. Gasses from the oxidizer were bubbled into a CO2 -gathering liquid scintillation cocktail. The efficiency of C02-trapping was determined before each day s samples were oxidized. The amount of hen determined by liquid... 

Identification, isolation, and removal of (polyhydroxy)benzenes from the environment have received increased attention throughout the 1980s and 1990s. The biochemical activity of the benzenepolyols is at least in part based on thek oxidation—reduction potential. Many biochemical studies of these compounds have been made, eg, of enzymic glycoside formation, enzymic hydroxylation and oxidation, biological interactions with biochemically important compounds such as the catecholamines, and humic acid formation. The range of biochemical function of these compounds and thek derivatives is not yet fully understood. 

A heterocyclic ring may be used in place of one of the benzene rings without loss of biologic activity. The first step in the synthesis of such an agent starts by Friedel-Crafts-like acylation rather than displacement. Thus, reaction of sulfenyl chloride, 222, with 2-aminothiazole (223) in the presence of acetic anhydride affords the sulfide, 224. The amine is then protected as the amide (225). Oxidation with hydrogen peroxide leads to the corresponding sulfone (226) hydrolysis followed by reduction of the nitro group then affords thiazosulfone (227). ... 

In addition to nonheme iron complexes also heme systems are able to catalyze the oxidation of benzene. For example, porphyrin-like phthalocyanine structures were employed to benzene oxidation (see also alkane hydroxylation) [129], Mechanistic investigations of this t3 pe of reactions were carried out amongst others by Nam and coworkers resulting in similar conclusions like in the nonheme case [130], More recently, Sorokin reported a remarkable biological aromatic oxidation, which occurred via formation of benzene oxide and involves an NIH shift. Here, phenol is obtained with a TON of 11 at r.t. with 0.24 mol% of the catalyst. 

Table 15) highlights the stability of this system compared to the PS/MTO system (entry 6, Table 15), which shows a decrease in activity during recycling. This difference in behaviour may be due to the weaker interaction between MTO and the PS polymer, which is only accomplished by the physical envelopment of the benzene ring. The PVP/MTO combination was successfully used for other compounds of biological interest, such as ter-penes. Even highly sensitive terpenic epoxides, hke a-pinene oxide, can be obtained in excellent yields using polymer-supported MTO catalysts [73] (Scheme 20, Table 16). 

Masten et al. (1996) investigated the oxidation of chlorinated benzenes such as 1,2-dichlorobenzene (1,2-DCB), 1,3,5-trichlorobenzene (1,3,5-TCB), and pentanoic acid (PA). TCB is often generated as a by-product of pesticide manufacturing, while DCB is commonly manufactured as an insecticide or a fumigant for industrial odor control. Due to their resistance to biological treatments, PA is usually nonreactive with ozone but can react with hydroxyl radicals (Masten et al., 1996). 

The oxidation of benzene- 1,2-diols to benzo-l,2-quinones is also a process of considerable biological importance, and solutions of copper compounds in organic solvents frequently act as catalysts for the aerial oxidation of such compounds (Fig. 9-5). These reactions almost certainly involve sequential one-electron processes, as indicated in Fig. 9-6. In some cases, the semiquinone forms may be isolated. 

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