Mechanism of the First Order Decay of 2-Hydroxy-propyl-2-peroxyl Radicals and of 0 2~ Formation in Aqueous Solution

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 0 2~ and H + were measured to have the same rate constants. The formation of 0 2~ and H+ was measured in H20 and D 20 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 H 0 2‘ followed by dissociation into H+ and 0 2~ .