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

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Abstract
[In radiation-biological studies it has been shown that O2 has a strong sensitizing effect on living cells, an effect which is also important in the radiotherapy of cancer]. Hydroxyl radicals from the radiolysis of N2O/O2 (4:1 vol/vol)-saturated aqueous solutions were reacted with acetate ions (10-2 M). As measured by pulse radiolysis, the resulting .CH2CO2- radicals react with O2 yielding the corresponding peroxyl, .O2CH2CO2- (k = 1.7 .times. 109/M/s). These peroxyl radicals decay bimolecularly (2k = 1.5 .times. 108/M/s) giving rise to the products (G values in brackets) glyoxylic acid (2.7), glycolic acid (0.7), formaldehyde (1.4), CO2 (1.4), organic hydroperoxide (0.7) and H2O2 (2.5). O2 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) H2O2 and 2 molecules of glyoxylic acid (.apprx. 27%); (ii) O2, glycolic acid and glyoxylic acid (.apprx. 25%); (iii) hydrogen peroxide and 2 molecules of formaldehyde, CO2 and OH- (25%). These reactions do not involve free radicals as intermediates; there is some .**GRAPHIC**. (G .apprxeq. 0.5) formed in the decay of the peroxyl radicals, which is attributed to the decay of intermediate oxyl radicals (tetroxide .fwdarw. O2 + 2 .OCH2CO2-) by 1.2-H shift, O2 addition and .**GRAPHIC**. elimination, a reaction sequence which gives rise to glyoxylic acid (10%); The reaction of .**GRAPHIC**. with the organic peroxyl radical yields the hydroperoxide (13%). Reaction (iii) is a novel peroxyl radical reaction.