Reactions of Bis(2,4-dinitrophenyl) Phosphate with Hydroxylamine

For dephosphorylation of bis(2,4-dinitrophenyl) phosphate (BDNPP) by hydroxylamine in water, pH region 4−12, the observed first-order rate constant, kobs, initially increases as a function of pH, but is pH-independent between pH 7.2 and pH 10. The initial BDNPP cleavage by nonionic NH2OH (<0.2 M) involves attack by the OH group and follows first-order kinetics, but the overall initial reaction of BDNPP liberates ca. 1.7 mol of 2,4-dinitrophenoxide ion (DNP). This initial reaction generates a short-lived O-phosphorylated hydroxylamine, 2, followed by three possible reactions: (1) reaction of 2 with hydroxylamine, generating 2,4-dinitrophenyl phosphate (DNPP, 3), which subsequently forms DNP; (2) intramolecular displacement of the second DNP group and rapid decomposition of the cyclic intermediate to form phosphonohydroxylamine and eventually inorganic phosphate; (3) a novel rearrangement with intramolecular aromatic nucleophilic substitution involving a cyclic intermediate and migration of the 2,4-dinitrophenyl group from O to N. Values of kobs increase modestly with pH > 10, the reaction is biphasic, and the yield of DNP increases. An increase in [NH2OH] also increases the yield of DNP, due largely to accelerated hydrolysis of DNPP.