Salt Effects on Solvolysis Reactions of p-Nitrophenyl Alkanoates Catalyzed by 4-(Dialkylamino)pyridine- Functionalized Polymer in Buffered Water and Aqueous Methanol Solutions

Abstract

Specific salting-in effects that lead to striking substrate selectivity were observed for the hydrolysis of p-nitrophenyl alkanoates 2 (n = 2−16) catalyzed by 4-(dialkylamino)pyridine-functionalized polymer 1 in aqueous Tris buffer solution at pH 8.0 and 30 °C. Macromolecule 1 was found to exhibit clear substrate preference for 2 (n = 6) in 0.05 M aqueous Tris buffer solution, as contrasted with the corresponding reaction in 0.05 M aqueous phosphate or borate buffer solutions where the substrate selectivity is absent. The formation of a reactive catalyst−substrate complex, 1·2, appears to be promoted by the presence of tris(hydroxymethyl)methylammonium ion, an efficient salting-in agent, from the Tris buffer system. The salting-in effect on formation of 1·2 complex is presumed responsible for the substrate specificity. The salting-out effects of sodium chloride on the solvolysis of 2 catalyzed by 1 were also investigated in 1:1 (v/v) methanol−water solution at pH 8.0 and 30 °C. The rate of 1-catalyzed sol...