Mechanism of proton removal from 2-phenylazoresorcinol monoanion by hydroxide ion in 95%(v/v) dimethyl sulphoxide–water

Abstract

Dissociation of the hydrogen-bonded proton from 2-phenylazoresorcinol monoanion requires high concentrations of sodium hydroxide in aqueous solution but occurs at low hydroxide ion concentrations in 95%(v/v) Me2SO–H2O. Kinetic studies in 95%(v/v) Me2SO–H2O show that proton removal takes place by single-step attack of hydroxide ion on the hydrogen-bonded proton and by a two-step process through a non-hydrogen-bonded open form, with half-lives for the reaction in the range 8–20 µs.