The Activation Parameters for Polymeric Imidazole Catalysis. The Efficiency of Multifunctional Catalysis on a Polymer Chain¹

Conformational effects and cooperative interactions in poly[5(6)-vinylbenzimidazole]-catalyzed solvolyses of anionic, long-chain substrates

“…The enhanced catalytic activity of the polymer at high pH values was attributed to a bifunctional catalysis involving both neutral and anionic pendant benzimidazole groups (4). The existence of multifunctional interactions in the poly-[5(6)-vinylbenzimidazolel-catalyzed solvolyses was further supported by a study of the activation parameters of these reactions and those of benzimidazole, N-methylimidazole, imidazole, poly [N-vinylimidazole] and poly [4(5)-vinylimidazole] (5). In order to investigate further the contribution of apolar and electrostatic interactions for the macomolecule-substrate complex formation, the solvolytic reactions of various negatively charged long aliphatic chain esters catalyzed by poly [5(6)-vinylbenzimidazole] (relative to the catalytic activity of the monomeric analog, benzimidazole) were investigated in different compositions of alcohol-water and at different pH values.…”

Synthesis of Polymeric Enzyme-like Catalysts

“…44 -vinylimidazole] as well as PEI have been utilized as backbones of catalysts in 1960's and 1970's. 9,[45][46][47][48][49][50] Without specific binding sites for substrates or active sites comprising convergent catalytic groups, however, these polymers and their derivatives behave simply as polymicelles equipped with functional groups. To overcome these limitations, we started to create binding sites on the backbones of synthetic polymers.…”

Solvolysis of p-nitrophenyl esters catalyzed by oligo-4(5)-vinylimidazoles

“…The catalytic solvolysis ofp-nitrophenyl acetate (PNPA) by poly-4(5)-vinylimidazole has been studied in 28.5 % ethanol-water (I) and a 10 % methanol-water solution (2) at a pH range of 7-9. In both cases, the k,,, vs. CL, (fraction of neutral imidazole on the polymer) profile showed an upward curvature.…”

“…The terms containing cr2 can, therefore, be minimized. The rate equation for the solvolysis of PNPA catalyzed by poly-4(5)-vinylimidazole at a pH range of 7-9 can, therefore, be simplified to kc,, = k, cc1 + kz ai* r Submitted in partial fulfillment of the requirements for the Ph.D. degree in Chemistry at The University of Michigan, 1970. The existence of bifunctional neutral-neutral imidazole interaction was indicated by a marked decrease in enthalpy and entropy of activation (dH2+, dS2+, respectively), for the solvolysis of PNPA by poly-4(5)-vinylimidazole (2). The imidazole-catalyzed imidazole catalysis in a concentrated monomeric imidazole solution was previously observed during the solvolysis of p-nitrophenyl benzoates substituted by an electronwithdrawing group (4), and of p-substituted phenyl acetate substituted by an electrondonating group (5).…”

“…Two possible mechanisms were proposed (2,6) which describe the interaction of two neutral imidazole pendent groups on the polymer chain with a substrate: (a) proton withdrawal from imidazole by another imidazole with a simultaneous catalytic solvolysis of the substrate by nucleophilic attack, as shown in (3), (b) a stepwise formation of a tetrahedral intermediate between the substrate and imidazole followed by a catalytic hydrolysis induced by another imidazole group, as shown in (4). A…”