Acid-catalysed solvolysis of 2-diazo-4′-methoxy- and 2-diazo-2-phenyl-acetophenone in aqueous–organic mixtures

Abstract

Rate constants for the hydrolysis of 2-diazo-4′-methoxy- and 2-diazo-2-phenyl-acetophenone are reported together with H₀ acidity functions in dimethyl sulphoxide–water, ethanol–water, and methanol–water mixtures containing dilute perchloric acid. The hydrolysis of 2-diazo-2-phenylacetophenone has been studied in ‘neutral’ dioxan–water mixtures and in dioxan–water mixtures containing 0.1 M-hydrochloric or -perchloric acid. Results of some kinetic isotope effect studies are reported. Graphs of log (observed rate constant) against H₀ are linear for reactions in perchloric acid solutions of fixed solvent composition. The effects of changing the solvent composition in the presence of 0.1 M-acid are correlated by plotting H₀+ log (observed rate constant) against log (activity of water). 2-Diazo-4′-methoxyacetophenone appears to hydrolyse by an A-1 mechanism in all the solvent mixtures studied. The kinetic behaviour of 2-diazo-2-phenylacetophenone is less consistent: in some conditions an A-2 route seems to be preferred; in others an A-S_E2 route seems more likely; in some cases the reaction is not first order.