EFFECTS OF SURFACTANTS ON SOLVOLYSIS OF P-NITROPHENYL ALKANOATES CATALYZED BY 4-(DIALKYLAMINO)PYRIDINE-FUNCTIONALIZED POLYMER IN AQUEOUS METHANOL SOLUTION

摘要

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 H2PO4-/HPO42-, 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-1 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. [References: 26]