Effects of Surfactants on Solvolysis of p-Nitrophenyl Alkanoates Catalyzed by 4-(Dialkylamino)pyridine-Functionalized Polymer in Aqueous Methanol Solution

Abstract

Catalysis of the solvolysis of p-nitrophenyl alkanoates 2 (n = 2-18) by 4-(dialkylamino)pyridine-functionalized polymer 1 in the presence of sodium n-dodecyl sulfate (SDS), n-dodecyltrimethylammonium bromide (DTAB), and heptaethylene glycol n-dodecyl ether (HEGDE) was investigated in 50:50 (v/v) methanol-water buffer (0.05 M H 2 PO 4 - /HP0 4 2- , pH 8.0) solution. Strikingly, a large rate enhancement is observed in the presence of anionic surfactant SDS for the solvolysis of 2 (n = 10-18) as compared with the corresponding reaction catalyzed by 1 or SDS alone. SDS is believed to bind both substrate and catalyst within micellar aggregates and influence reactivity by a combination of catalyst-substrate proximity and micellar microenvironment. In the presence of HEGDE, no significant effects on the 1-catalyzed solvolysis of 2 (n < 8) were observed. At (2.5-7.5) x 10 -5 unit mol L -l 1, the solvolysis rate exhibits a modest decrease for 2 (n = 10 and 12) and a modest increase for 2 (n = 14, 16, and 18) with added nonionic surfactant HEGDE. The solvolysis rate for 1-catalyzed solvolysis of 2 (n = 2 -18) was found to be unchanged by cationic surfactant DTAB in aqueous methanol solution.