Mechanism of the reaction of radicals with peroxides and dimethyl sulfoxide in aqueous solution

The reactions of methyl and methylperoxyl radicals derived from dimethyl sulfoxide (DMSO) with hydrogen peroxide, peroxymonocarbonate (HCO ₄^-), and persulfate were studied. The major reaction observed for the hydroperoxides was the abstraction of the hydrogen atom by the radicals. The radicals interact with a lone pair of electrons on the peroxide to produce methanol and formaldehyde. Furthermore, the results indicate that in RO₂H and RO₂R′, electron-withdrawing groups cause a considerable increase in the reactivity of the peroxides towards the radicals and not only towards nucleophiles. The HO₂^·/O ₂^·- and CO₃^·- radicals react with DMSO to produce methyl radicals. Thus, the formation of the ^·CH₃ radicals in the presence of DMSO is not proof of the formation of the ^·OH radicals in the system. These reactions must be considered when radical processes, such as in biological and catalytic systems, are studied. Especially, the plausible role of HCO ₄^- ions in biological systems as a source of oxidative stress cannot be over-looked.