Radicals from peroxides

Thermal decomposition of hydroxyalkyl hydroperoxyalkyl peroxides produces mixtures of starting carbonyl compounds, mono- and dicarboxyHc acids, cycHc diperoxides, carbon dioxide, and water. One specific hydroxyalkyl hydroperoxyalkyl peroxide from cyclohexanone (2, X = OH, Y = OOH) is a soHd that is produced commercially as a free-radical initiator and bleaching agent (see Table 5). On controlled decomposition, it forms 1,12-dodecanedioic acid (150). 

The original compound, maleimide (2,5-dioxo-A -pyrroline), is synthesized by the cyclo-condensation of ammonia and maleic acid. Similarly, primary amine is added to maleic anhydride, followed by cyclocondensation, to form N-substituted maleimide (Fig. 2). This reaction is applied to the preparation of bis-maleimides (BMl) [1]. At first, BMI was used as a crosslinking agent for natural rubber (NR). An o-dichlorobenzene solution of NR was crosslinked by BMI at I08-150°C in the presence of peroxides. The radicals generated from peroxides react with the double bonds of both BMI and NR [ 1 ]. 

Since the benzene emission in the thermal decomposition of benzoyl peroxide results from radical transfer by the phenyl component of a benzoyloxy-phenyl radical pair, phenyl benzoate produced by radical combination within the same pair should appear in absorption. A weak transient absorption has been tentatively ascribed to the ester (Lehnig and Fischer, 1970) but the complexity of the spectrum and short relaxation time (Fischer, personal communication) makes unambiguous assignment difficult. Using 4-chlorobenzoyl peroxide in hexachloro-acetone as solvent, however, the simpler spectrum of 4-chlorophenyl 4-chlorobenzoate is clearly seen as enhanced absorption, together with... 

Evidence that oxidized lipids play a role in the pathogenesis of RA comes from studies demonstrating the presence of lipid products arising from radical attack in rheumatoid synovial fluid. This is consistent with oxidation reactions occurring locally in the joint. Lipid peroxidation products that react with thiobarbituric acid (TBARs) have been detected in rheumatoid knee-joint synovial fluid (Rowley et /., 1984). In addition, the... 

The first radicals to be studied were, hardly surprisingly, those that were somewhat less reactive, and thus capable of rather longer independent existence. The first such radical to be detected unequivocally was Ph3C- (4), obtained in 1900 on reacting Ph3CCl with finely divided silver (cf. p. 43). The radical reacted with halogens to reform the triphenylmethyl halide (5), or with oxygen from the air to form (6), a peroxide (all radicals react readily with 02 from the air) ... 

Organometallic formation may result from a chain mechanism [Eqs. (21)-(23) and (18)—(20)] and/or radical displacement [Eqs. (21)-(23), alone]. The reaction of 13C-labeled mercuric cyclohexanoate with cyclohexylcarbonyl peroxide (1 1) gave mainly unlabeled organomercu-rial, which was derived from radical displacement (122). Decarboxylation by a chain mechanism was reported for the syntheses of organomercuric carboxylates of straight chain alkyls [R = Me(CH2) , n - 0-8, 10, or 15 (123-131)], branched alkyls [R = Me2CH(CH2) , n = 0 or 2 (132) or Me3C(CH2) , n = 0-2 (133)], substituted alkyls [R = cyclopentylmethyl... 

Generated from diacetyl peroxide, methyl radicals attack 2-methylfuran at position 5 preferentially if both 2- and 5-positions are occupied as in 2,5-dimethylfuran there is still little or no attack at the 3(4)-position. If there is a choice of 2(5)-positions, as in 3-methylfuran, then that adjacent to the methyl substituent is selected.249 These orientation rules are very like those for electrophilic substitution, but are predicted for radical attack by calculations of superdelocalizability (Sr) by the simple HMO method. Radical bromination by IV-bromsuccinimide follows theory less closely, presumably because it does not occur through a pure radical-chain mechanism.249... 

Since the analogous peroxides usually decompose by a free radical mechanism, it is noteworthy that this hydroxamic acid is not sensitive to the action of free radicals from anisoyl peroxide. A radical chain mechanism like that shown below can therefore be ruled out for this compound. 

The primary ozonation by-products of atrazine (15 mg/L) in natural surface water and synthetic water were deethylatrazine, deisopropylatrazine, 2-chloro-4,6-diamino-s-triazine, a deisopropylatrazine amide (4-acetamido-4-amino-6-chloro-5-triazine), 2-amino-4-hydroxy-6-isopropylamino-5-triazine, and an unknown compound. The types of compounds formed were pH dependent. At high pH, low alkalinity, or in the presence of hydrogen peroxide, hydroxyl radicals formed from ozone yielded 5-triazine hydroxy analogs via hydrolysis of the Cl-Cl bond. At low pH and low alkalinity, which minimized the production of hydroxy radicals, dealkylated atrazine and an amide were the primary byproducts formed (Adams and Randtke, 1992). 

TABLE 9. Rate constants for the formation of di-tertiary alkyl peroxides from tertiary alkylperoxy radicals ... 

The heme iron in the peroxidase is oxidized by the peroxide from III+ to V4- in compound I. The compound I is reduced by two sequential one-electron transfer processes giving rise to the original enzyme. A substrate-free radical is in turn generated. This may have toxicological implications. Thus the myeloperoxidase in the bone marrow may catalyze the metabolic activation of phenol or other metabolites of benzene. This may underlie the toxicity of benzene to the bone marrow, which causes aplastic anemia (see below and chap. 6). The myeloperoxidase found in neutrophils and monocytes may be involved in the metabolism and activation of a number of drugs such as isoniazid, clozapine, procainamide, and hydralazine (see below). In in vitro systems, the products of the activation were found to be cytotoxic in vitro. 

Both the methyl (CH3) and the peroxide (HO2) radicals are comparably unreactive. The low reactivity of CH3 is part of the explanation that the oxidation characteristics of methane are different from those of higher hydrocarbons. 

Small, but measurable frequency shifts have also been observed for v3 in selectively deuterated peroxide crystals. Although it is not clear whether these perturbations arise from size or polarizability differences between C—H and C—D, their existence allows us to identify contacts between C02 and certain methylene groups in nearby peroxides and radicals. 

The peroxide-free radicals capture a hydrogen ion from another fat molecule, forming a hydroperoxide and another fatty free radical ... 

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