Hydrogen peroxide decomposition intermediate oxidation reactions

The XH can be the parent hydrocarbon but is more usually an intermediate oxidation product with weaker C—H bonds, such as an aldehyde or alkene. Even so, the abstraction reaction has a large activation energy, as does the hydrogen peroxide decomposition (which is also pressure dependent), so that the branching mechanism tends to be of greater importance towards the higher temperature and pressure part of the region. 

With radical sources other than acyl peroxides, the rearomatization of the a-complex can take place by various, not always well characterized, reactions, such as oxidation by metal salts, hydrogen abstraction by intermediate radicals, disproportionation, and induced decomposition. 

Reaction of 3,5-disubstituted-1,2,4-trioxolanes (89) with oxidants (usually under basic conditions) leads to carboxylic acids (Equation (14)). This reaction is often carried out as the work up procedure for alkene ozonolysis, avoiding the need to isolate the intermediate ozonide. Typical oxidants are basic hydrogen peroxide or peracids and this type of oxidative decomposition is useful for both synthetic and degradative studies. 

The subsequent reaction of the peroxo complexes with bromide gives oxidized bromine species (see Scheme 2). HOBr, Br2, and Br3 rapidly equilibrate, and Br3 is the predominant spectrophotometrically observed intermediate (Xmax 267 nm e = 36,100 M-1 cm-1) in the absence of an organic substrate. Tribromide is stabilized with respect to HOBr, Br2 and decomposition products by high bromide and acid concentrations (34). HOBr is reduced by excess hydrogen peroxide to yield bromide, water, and dioxygen, of which dioxygen can be measured. In the presence of TMB, the oxidized species is rapidly consumed in the bro-mination of TMB to BrTMB. Quantitation of BrTMB demonstrates that bromination is stoichiometric with respect to the concentration of H202 added. Thus TMB is a rapid, quantitative trap for the oxidized bromine species (33). 

Baldwin and Walker [99] have pointed out that, from kinetic considerations, surface reactions of alkylperoxy radicals cannot play a significant role except at very low overall rates of reaction and conclude that it is more likely that surface destruction of relatively stable intermediates such as the alkyl hydroperoxides or hydrogen peroxide are the main cause of surface effects in hydrocarbon oxidation. Luckett and Pollard [68, 134] have provided evidence, which suggests that the surface destruction of tert-butylhydroperoxide is indeed important during the oxidation of isobutane below ca. 320 °C. Since isobutene and acetone are known products of the decomposition of tert-butylhydroperoxide, it is clear that many of the foregoing results can be explained in these terms, but if this is the predominant heterogeneous reaction the yield of acetone would be... 

The oxidation reactions of 2,4,5-triphenylimidazole (lophine) have received considerable attention. With chromic acid it gives benzamide and benzanilide, but even more interest has centred on its involvement in the phenomenon of chemiluminescence. Some of this material has been discussed earlier (Sections 4.06.3.6, 4.07.1.2.1 and 4.07.1.2.3). The oxidative decomposition of lophine in the presence of air is accompanied by the emission of light, and it is the excited singlet state of the diaroylarylamidine (12 Scheme 2) which is the light emitter. The radical (46) derived from oxidation of lophine with aqueous ferricyanide and ethanolic KOH forms a hydroperoxide with hydrogen peroxide with consequent luminescence. When 2,4,5-tri- and 1,2,4,5-tetra-phenylimidazoles are oxidized in dilute methanol solution in the presence of methylene blue, the dibenzoylbenzamidine is also formed under circumstances in which hydroperoxides cannot be intermediates (B-76MI40701). 

In addition to the S(IV) —H202 reaction, the reactions of other peroxides such as peroxymonosulfate, peroxyacetic acid, and methyl hydroperoxide with S(IV) are also sensitive to specific-acid catalysis (Hoffmann and Calvert, 1985). The rate of oxidation of S(IV) by HSO / is comparable to the rate of oxidation of S( IV) by hydrogen peroxide (Betterton and Hoffmann, 1988). We have proposed a general mechanism for the ROOH-S(IV) reaction in which the rate-determining step involves the acid-catalyzed decomposition of a peroxide-bisulfite intermediate. The rate expression applicable for this mechanism is... 

A special type of redox reaction is the disproportionation reaction. In a disproportionation reaction, an element in one oxidation state is simultaneously oxidized and reduced. One reactant in a disproportionation reaction always contains an element that can have at least three oxidation states. The reactant itself is in an intermediate oxidation state that is, both higher and lower oxidation states exist for that element. The decomposition of hydrogen peroxide is an example of a disproportionation reaction ... 

For the Fenton oxidation, reactions involving the organic molecules instead of hydrogen peroxide were written for the last step. It can be seen that the competitibn between the ferrous salt and hydrogen peroxide for the complex determines the extent to which there is catalytic decomposition. This is consistent with his observations that n increases with increase of [H202]/[Fe++] but it does not explain the ultimate limit which n reaches. Manchot and Pflaum (52) wrote similar reactions involving the intermediate FeSCh HaCh). 

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