Cooperative effects involved in esterolytic reactions of cationic long chain esters catalyzed by benzimidazole-containing polymers

Abstract

The solvolyses of positively charged esters with varying chain length catalyzed by benzimidazole, poly[5(6)-vinylbenzimidazole] and copolymers of 5(6)-vinylbenz-imidazole with acrylic acid were studied. Poly[5(6)-vinylbenzimidazole] showed a marked selectivity for the positively charged esters with varying aliphatic chain length but the catalytic activity was suppressed. In order to investigate the more detailed characteristics of the 5(6)-vinylbenzimidazole-acrylic acid copolymers in the solvolyses of these esters, the effects of copolymer composition on their catalytic activities were studied. In the solvolyses of every ester employed, the copolymer compositions affected their catalytic activities. In 40% 1-propanol-water the activities of the copolymers indicated a strong dependence on the carboxylatebenzimidazole-carboxylate triad. These effects were due to strong electrostatic interactions between these sequences and the substrates. The effects of solvent composition on the catalytic activities of the copolymer-catalyzed solvolyses were also investigated. The copolymers of 5(6)-vinylbenzimidazole with acrylic acid were found to have entirely different characteristics in methanol-water than in 1-propanol-water systems. The catalytic ability was found to be a function of the benzimidazole content and on the size of the substrate. Apolar interactions became a dominant force in the methanol-water system.