Reactions in strongly basic solutions. Part III. Correlation of the rate of alkaline hydrolysis of 1-substituted 2,4-dinitrobenzenes in aqueous dimethyl sulphoxide with an acidity function. Details of the mechanistic pathway

Abstract

The rate coefficients for the alkaline hydrolysis of a series of 1-substituted 2,4-dinitrobenzenes have been measured in aqueous dimethyl sulphoxide (DMSO) at 30·0°. These rates have been correlated with an acidity function of the medium. Linear relations exist at lower DMSO contents but, normally, pass through a maximum in the region of 55–70 mol % DMSO. Studies of the rate–acidity function relations, substituent effects, the occurrence and decay of Meisenheimer complexes, activation parameters, and the effect of added salts enable a detailed mechanism to be indicated. At low DMSO contents, the formation of the 1,1-Meisenheimer complex is rate-determining. As the DMSO content is raised, the contribution to the overall reaction rate of the decomposition of a 1,3-Meisenheimer complex appears to become important. At very high DMSO contents, the decomposition of the 1,1-complex appears to become rate determining.