Reactions of phosphate radicals with organic compounds

Phosphate radicals in the three acid-base forms, H2PO4, HPO4-, and PO42-, were produced by the reaction of hydrated electrons with peroxodiphosphate ions at pH values of 3-4, 7-9, and 12, respectively. Rate constants for the reactions of these radicals with organic compounds were determined by following the rate of decay of the phosphate radical absorption in the presence of increasing concentrations of the substrate. Rates of reaction of H2PO4 were found to be higher than those of HPO4- and PO42- by a factor of approximately 4-10, while the latter radicals have similar rates. The rate constants for hydrogen abstraction from aliphatic compounds ranged from approximately 105 M-1 s-1 for acetic acid and 2-methyl-2-propanol to approximately 108 M-1 s-1 for 2-propanol and formate. Addition to a double bond was not faster but reaction with aromatic compounds reached a rate constant greater than 109 M-1 s-1 for the most reactive compounds. The effects of substituents were found to be similar for H2PO4 and SO4- and both radicals are suggested to react with the aromatic ring by one-electron transfer to the inorganic radical. In hydrogen abstraction reactions H2PO4 (and SO4-) were found to react with rate constants approximately 10-100 times lower than those of OH and to have a selectivity about three times higher than that of OH. Radiolytic chain decomposition of peroxodiphosphate in the presence of some organic compounds was also studied