Arrhenius parameters for the alkaline hydrolysis of glycine ethyl ester, in aqueous solution, and thermodynamic functions for its ionisation as an acid

Abstract

The kinetics of the alkaline hydrolysis of glycine ethyl ester have been studied in aqueous solution over a wide range of pH at 0, 25, 35·5, 41·95, and 49·45°. Corrections have been made to account for protonation of the reactant ester and the product, glycine. The effect of ionic strength on the reaction rate is discussed. The results are consistent with a reaction scheme which involves two simultaneous second-order reactions of hydroxide ion with the non-protonated and protonated forms of the ester. Rate constants describing these two reactions have been found from the composite observed rate constant at all temperatures, and corresponding Arrhenius parameters are reported. Surprisingly, the reaction of the protonated ester seems to have the lower activation energy. The equilibrium constant for the ionisation of the ester as an acid has been studied as a function of ionic strength, and of temperature. Values of ΔG°, ΔH°, and ΔS° for this ionisation are reported.