Electron spin resonance studies. Part L. Reactions of alkoxyl radicals generated from alkyl hydroperoxides and titanium(III) ion in aqueous solution

Abstract

A variety of alkoxyl radicals has been generated in aqueous solution by the one-electron reduction of alkyl hydroperoxides by titanium(III) ion, and their behaviour has been studied by e.s.r. spectroscopy in conjunction with a rapid-flow system. Although the alkoxyl radicals themselves are not directly detectable by e.s.r., both the adducts which they form with the spin-trap CH₂:NO₂^– and the carbon-centred radicals into which they are transformed can be monitored; in this way, a novel 1,2-shift [e.g. PrO·→·CH(OH)Et], as well as intramolecular 1,5-hydrogen transfer, intramolecular addition to an olefinic bond, and fragmentation, have been demonstrated. Estimates have been obtained for the rate constants for some of these processes (e.g. that for the 1,2-shift mentioned is ca. 10⁷ s^–1). and the behaviour of alkoxyl radicals in aqueous and non-aqueous media has been compared.