The Esterolytic activity of poly(N-alkylimidazoles) in ethanol-water. The poly(1-methyl-5-vinylimidazole)-catalyzed hydrolysis of p-nitrophenyl acetate and 3-nitro-4-acetoxybenzoic acid

Abstract

1-Methyl-4-vinylimidazole (1-Me-4-VIm) and 1-methyl-5-vinylimidazole (1-Me-5-VIm) have been synthesized and polymerized. The esterolytic activity of these polymers in 28.5% ethanol-water toward p-nitrophenyl acetate (PNPA) and 3-nitro-4-acetoxybenzoic acid (S2-) has been evaluated as compared to that of the model compounds 1,4-dimethylimidazole (1,4-DMIm) and 1,5-dimethylimidazole (1,5-DMIm). Poly(l-methyl-4-vinylimidazole) [poly(1-Me-4-VIm)] and 1,4-DMIm are not catalytically active, as compared to buffer solution, toward PNPA and S2- in 28.5% ethanol-water. The rate of hydrolysis of PNPA by 1,5-DMIm and poly(1-methyl-5-vinylimidazole) [poly(l-Me-5-VIm)] was proportional to the concentration of neutral imidazole residues for both catalysts; however, 1,5-DMIm was five times more active than poly(1-Me-5-VIm). Poly(1-Me-5-VIm) displayed a bell-shaped pH-rate profile toward the negatively charged ester S2- while the rate of hydrolysis by 1,5-DMIm was again proportional to the concentration of neutral imidazole. At their respective optimum pH's, poly(1-Me-5-VIm) was 20% more active than 1,5-DMIm.