The reactions of organic phosphates. Part VII. The mechanisms of hydrolysis of neopentyl dihydrogen phosphate and a comparison with methyl dihydrogen phosphate

Abstract

Neopentyl dihydrogen phosphate shows an acid-catalysed hydrolysis whose rate increases smoothly with acid concentration. Unlike the acid-catalysed hydrolysis of p-acetylphenyl and p-nitrophenyl dihydrogen phosphates, no rate maximum is observed in strong acid solution, although all three reactions proceed with phosphorus–oxygen bond fission. Because of its greater protonating power, sulphuric acid is a slightly better catalyst than hydrochloric acid. In contrast, the rate of hydrolysis of methyl dihydrogen phosphate in strong acid solution is greatly increased by the presence of halide ions, which act as nucleophiles towards the neutral and conjugate acid species. Both these processes proceed by carbon–oxygen bond fission and involve simple S_N2 displacements on the methyl carbon atom.