Alkaline ethanolysis of methyl 4-hydroxybenzoate and hydrolysis of methyl and ethyl 4-hydroxybenzoates in ethanol—water systems

Abstract

Kinetics of the simultaneous hydrolysis and ethanolysis of methyl 4-hydroxybenzoate were studied in 0.5 mol dm −3 alkali in ethanol-water mixtures. Rates of hydrolysis of the ethyl ester, an intermediate product, were also evaluated in these solvent systems. Kinetics of the ethanolysis of the methyl ester were further studied in ethanol in the presence and absence of 0.5 mol dm −3 alkali. Rates of the aqueous hydrolysis reactions of both esters were also studied in 0.5 mol dm −3 alkali. Approximately a 100-fold reduction in the rate of hydrolysis of the methyl ester in 82.43% w/w ethanol occurred compared with water. The majority of this effect was over the solvent range from water to 50% w/w ethanol. Rate changes with solvent composition for ethanolysis of methyl ester were dominated by changes in the ΔH ∗ values. Larger changes in ΔH ∗ and ΔS ∗ values were exhibited for the hydrolysis reactions. These values were, however, compensatory on the reaction rate, a maximum in this compensation occurring at ≅ 10% w/w of ethanol. Hence addition of ethanol to an alkaline aqueous solution of methyl 4-hydroxybenzoate resulted in a markedly reduced rate of hydrolysis, and formation of the ethyl ester over the temperature range 25.0–46.1°C studied. This ester subsequently underwent a slower hydrolysis reaction when compared with the methyl ester.