Mechanism of the First Order Decay of 2-Hydroxy-propyl-2-peroxyl Radicals and of O2~ Formation in Aqueous Solution

Abstract

Using time resolved ESR spectroscopy and photoflash conductivity the uncatalysed, first order decay of 2-hydroxy-propyl-2-peroxyl radicals and the uncatalysed, first order generation of O2 ·̅ and H+ were measured to have the same rate constants. The formation of O2 ·̅ and H+ was measured in H2O and D2O and a kinetic isotope effect of kH/k =D3.5 was obtained. Comparing the rate constants of the peroxyl radicals derived from methanol, ethanol and 2-propanol it was shown that the rate constant increases with increasing methyl-substitution. In 2-propanol water mixtures the rate constant of the 2-hydroxy-propyl-2-peroxyl radical increases only slightly with increasing polarity of the solvent. The experimental results are in accord with a mechanism which involves a cyclic transition state leading to a concerted elimination of HO2· followed by dissociation into H+ and O2 ·̅.