Control of Substrate Specificity in Polymer-Catalyzed Solvolysis Reactions of p-Nitrophenyl Alkanoates by Changing the Buffer System

Abstract

The substrate specificity in solvolysis reactions of p-nitrophenyl alkanoates 2 (n = 2−18) catalyzed by 4-(dialkylamino)pyridine-functionalized polymer 1 was examined in buffered aqueous methanol solution at pH 8.0 and 30 °C. The chemical reactivity and substrate specificity in this catalytic system were found to be controlled by changing the buffer system. In 1:1 (v/v) methanol−aqueous phosphate buffer solution, macromolecule 1 exhibits substrate specificity for 2 (n = 14) below 1.0 × 10-5 unit mol L-1, and the substrate specificity changes from 2 (n = 14) to 2 (n = 12) as the concentration of 1 increases to 2.5 × 10-5 unit mol L-1 and changes again from 2 (n = 12) to 2 (n = 10) when the concentration of 1 increases further to 7.5 × 10-5 unit mol L-1. However, in 1:1 (v/v) methanol−aqueous Tris buffer solution, macromolecule 1 was found to demonstrate the same substrate specificity for 2 (n = 14) when the concentration of 1 is increased from 5.0 × 10-6 to 1.0 × 10-4 unit mol L-1. The control of substrate specificity by the change of the buffer system is believed to be unprecedented for catalysis of ester solvolysis.