On the Mechanism of Ester Aminolysis in the Presence of Alkylammonium Carboxylate Reversed Micelles

Article abstract of DOI:10.1021/jo00147a019

The mechanism of ester aminolysis by alkylammonium carboxylate reversed micelles was examined.There are two possible pathways, one involving the carboxylate group of the surfactant acting as a general base and another in which it is acting as a nucleophile.The latter mechanism involves the formation of a mixed anhydride (derived from the surfactant and the ester) leading, on aminolysis, to two amides.It was not possible to detect the formation of the intermediate anhydride.Careful analysis of the reaction products showed that only one amide, that derived from ester,is formed.Thus the second mechanism is in error.The nature of the slow step was explored by studying the aminolysis of a series of esters: p-X-phenyl acetates (where X = CH3O, CH3, H, Br, CN, and NO2) by dodecylammonium propionate (DAP) and by dodecylamine plus DAP in benzene and in cyclohexane.Excellent correlations between the logarithm of the rate constant and the Hammett (?^-) values were obtained.This implies that the phenoxide ion is the leaving group and that the slow step probably involves the collapse of the tetrahedral intermediate formed by the attack of the amine on the ester.Thus it appears that ester aminolysis in the micellar pseudophase and that in aprotic solvents proceed with the same mechanism and rate-limiting step.