Temperature-jump study of the kinetics of reactions of arylethylmalonate monoanions with hydroxide ion. The effect of ring substituents

Abstract

The second-order rate constants kf of proton transfer reactions from ring-substituted arylethylmalonate mono-anions toward hydroxide ions, AH–+ OH–→ A2–+ H2O, in aqueous solution were measured by the temperature-jump relaxation method. The equilibrium constants K for the reversible reactions were also determined by potentiometric titrations. Logarithms of both the rate and equilibrium constants obtained at 33 °C were found to be linearly correlated with Taft's substituent constants σ0; log kf,X/kf,H= 0·38σ0 and log KX/KH= 0·93σ0. The results clearly indicate that the rates of both the forward and backward reactions are influenced by the electronic effects of substituents.