Tetra-alkylammonium carboxylate and imidazole promoted esterolysis in benzene. A catalytic model related to the charge relay system of trypsin enzymes

Abstract

The esterolysis of p-nitrophenyl propionate in benzene in the presence of 3–4 × 10^–3M amounts of imidazole is very effectively promoted by addition of tetra-alkylammonium carboxylates. The esterolysis rate in the presence of 3–4 × 10^–3M amounts of tetra-alkylammonium carboxylates is enhanced by addition of imidazole up to the point where their molar ratio is ca. 1 : 1 and then inhibited by further addition. From the analysis of the kinetic effects observed, including those of water, it is suggested that the main catalytic system is a preformed hydrogen-bonded carboxylate ion–imidazole pair which utilizes the nucleophilic and basic properties of the unsolvated RCO₂^– anion through the relay action of the imidazole.