Hydroxyl radical reaction with phosphate esters and the mechanism of phosphate cleavage

The reaction of hydroxyl radicals with several phosphate esters in irradiated aqueous solutions has been followed by esr observation of the radicals and by determination of the yield of inorganic phosphate. The initial step of hydrogen abstraction takes place at all available C-H positions and, as expected, the site of reaction was found to be affected by the state of protonation of an amino group. In most cases the radicals produced by abstraction were observed by esr and in certain cases the radicals subsequently produced by elimination of H₂O or H₃PO₄ were also observed. The results for phospho glycols indicate that α-phospho radicals are the most stable toward phosphate elimination but that β-phospho radicals undergo elimination of H₃PO₄ very rapidly. Elimination of H₂O from these and other radicals appears to be slower than that of H₃PO₄. The results for ethanolamine and serine phosphates indicate that the elimination of H₃PO₄ from the radicals is slower than in the case of glycol phosphates and probably does not take place at all when the amino group is protonated.