Elucidation of the mechanisms of peroxyl radical reactions in aqueous solutions using the pulse radiolysis technique

Abstract

In the investigation of peroxyl radicals the pulse radiolysis technique can be used with some advantage to determine the rate of their unimolecular or bimolecular decay. If the identities of the products of the peroxyl radical reactions are known, pulse radiolysis often provides evidence for mechanistic details. The absorptions of the peroxyl radicals are neither very specific nor strong and optical detection is usually of little help. However, there are many peroxyl radical reactions which result in the formation of HO2./H+O2. (pKa(HO2.)=4.7) or other acids. Thus in neutral and alkaline solutions such species can be monitored even quantitatively by the pulse conductometric method. Furthermore, O2. can be detected by its rapid reaction with tetranitromethane which yields the strongly absorbing nitroform anion. Since O2. is only a short-lived intermediate in neutral solutions, it can be distinguished from permanent acids which are often formed in peroxyl radical reactions. In alkaline solutions, where O2. is more stable, superoxide dismutase might be used with advantage to reduce its lifetime and to determine the yield of permanent acids. Some details of the fate of the peroxyl radicals derived from acetate, the β-hydroxyethyl-peroxyl radicals, and the cyclopentylperoxyl radicals will be reviewed.