Effect of hydroxide ion concentration on the partitioning of a monoanionic tetrahedral intermediate into di- and tri-anionic reactive intermediates in the alkaline hydrolysis of alloxan

Abstract

The alkaline hydrolysis of alloxan was studied within the hydroxide ion concentration range 0.02–3.0M at a constant ionic strength. The rate of hydrolysis was found to follow an irreversible first-order consecutive reaction path of the type A [graphic omitted] B [graphic omitted] X where k_1obs. and k_2obs. are pseudo-first-order rate constants and A,B, and X stand for alloxanic acid, intermediate, and ammonia, respectively. Three distinct regions were found to exist in the rate profiles. In the lower region, rate constants were found to follow the relations 1//_k1obs.=B₁+B₂//_[OH^–] and 1//_k2obs.=C₁+C₂//_[OH^–]. At relatively higher concentration the rate was independent of hydroxide ion concentration and at much higher concentration the rate constants followed the relations k_1obs.=D₁+D₁[OH^–]+D₃[OH^–]² and k_2obs.=E₁+E₂[OH^–]+E₃[OH^–]². In these relations B₁, B₂, C₁, C₂, D₁, D₂, D₃, E₁, E₂, and E₃ are arbitrary constants. On the basis of observed kinetic data, a possible mechanism has been proposed and various kinetically indistinguishable kinetic paths have also been discussed.