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-SE2 route seems more likely; in some cases the reaction is not first order.