Radiolytic chain decomposition of peroxomonophosphoric and peroxomonosulfuric acids

Radiolytic studies of peroxomonophosphoric acid, H3PO5, and peroxomonosulfuric acid, H2SO5, have been carried out over a wide pH range. Unlike the corresponding peroxodiacids, H4P2O8 and H2S2O8, the peroxomono acids undergo radiolytic chain decomposition, with G values increasing from about 6 to 60 in going from pH 1 to 12.6. Sharp rises in G values appear at pH values near the pK/sub a/ of the hydroperoxy proton (highest pK/sub a/). The mechanism suggested for these chain reactions involves successive oxidation and reduction of the parent compounds by radicals produced in the preceding step. Pulse radiolysis experiments showed that the reaction of e/sub eq/- with peroxomonophosphate (k = 4.4 x 10 M-1 s-1 at pH 7) produces OH radicals twice as frequently as HPO4- radicals. Previous results with peroxomonosulfate showed a factor of 4 for similar reactions. The rate constant for reaction of OH radicals with peroxomonophosphate at pH 7 was found to be 4.3 x 107 M-1 s-1, and with peroxomonosulfate 1.7 x 107 M-1 s-1 at pH 7 and 2.1 x 109 M-1 s-1 at pH 11. The reactions of OH are suggested to be the chain initiation step and possibly responsible for the main chain propagation as well