Acetate Peroxyl Radicals, ·O2CH2 CO2 -: A Study on the γ-Radiolysis and Pulse Radiolysis of Acetate in Oxygenated Aqueous Solutions

Hydroxyl radicals from the radiolysis of N2O/O2 (4:1 v/v)-saturated aqueous solutions have been reacted with acetate ions (10-2M). As measured by pulse radiolysis, the resulting ·CH2CO2 - radicals react with oxygen yielding the corresponding peroxyl radicals, ·O2CH2CO2 - (k = 1.7 x 109 M-1s-1). These peroxyl radicals decay bimolecularly (2k = 1.5 x 108 M-1s-1) giving rise to the products (G values in brackets) glyoxylic acid (2.7), glycolic acid (0.7), formaldehyde (1.4), carbon dioxide (1.4), organic hydroperoxide (0.7) and hydrogen peroxide (2.5). Oxygen is consumed with a G value of 5.3. Aided by data from pulse radiolysis it is concluded that the intermediate tetroxide formed upon the bimolecular decay breaks down by various routes to yield: (i) hydrogen peroxide and two molecules of glyoxylic acid (ca. 27%); (ii) oxygen, glycolic acid and glyoxylic acid (ca. 25%); (iii) hydrogen peroxide and two molecules of formaldehyde, carbon dioxide and OH- (25%). These reactions do not involve free radicals as intermediates; (iv) There is some O⨪ 2 (G ≈ 0.5) formed in the decay of the peroxyl radicals, which is attributed to the decay of intermediate oxyl radicals (tetroxide → O2 + 2 ·OCH2CO2 -) by 1,2-H shift, oxygen addition and HO2 · elimination, a reaction sequence which gives rise to glyoxylic acid (10%); (v) The reaction of O2 ⨪ with the organic peroxyl radical yields the hydroperoxide (13%). Reaction (iii) is a novel peroxyl radical reaction.