Reactions in strongly basic solutions. Part IV. Kinetics and mechanisms of the alkaline hydrolysis of 1-substituted 2,4-dinitrobenzenes in aqueous dioxan

Abstract

Rate coefficients for the alkaline hydrolysis of ten 1-substituted 2,4-dinitrobenzenes in a series of aqueous dioxan mixtures were measured at 50·0°. The kinetic solvent isotope effect was examined for all the substrates in 60% v/v aqueous dioxan. These results can be used to investigate the structure of the transition states. More ‘polar’ and less ‘advanced’ transition states appear to have k2H2O/k2D2Oca. unity; the corresponding rates decrease with increasing dioxan content. Less ‘polar’ and more ‘advanced’ transition states appear to have lower values for k2H2O/k2D2O; the corresponding rates increase with increasing dioxan content. The relation between the transition-state structure and the 1-substituent appears to arise mainly from steric effects. An H– acidity function could not be satisfactorily established in aqueous dioxan mixtures and the reasons for this result are discussed.