Multifunctional Hydrolytic Catalyses. 7. Cooperative Catalysis of the Hydrolysis of Phenyl Esters by a Copolymer of N-Methylacrylohydroxamic Acid and 4-Vinylimidazole

A bifunctional polymer catalyst was prepared by radical polymerization of benzyl N-methylacrylohydroxamate and 4-vinylimidazole, followed by the removal of the benzyl group, and the hydrolysis of four phenyl ester substrates was examined in 28.9 vol/vol % EtOH-H₂O at 30 °C. The Michaelis-Menten kinetics were observed only for a long-chain, anionic substrate. The major course of catalysis was acylation and deacylation at the hydroxamate group. The acylation process consisted of the simple nucleophilic attack of the hydroxamate anion (k_A^- ) and the general base (imidazole) catalyzed nucleophilic attack of the hydroxamic acid (k_HA)· In the case of p-nitrophenyl acetate (PNPA), K_HA and k_A-were 0.50 and 36 M^-1 s^-1, respectively, and the difference was much smaller for other substrates. The deacylation reaction proceeded efficiently due to the general-base catalysis of the imidazole group. Thus, the imidazole group acts as a general base in both the acylation and deacylation process, in close resemblance to the charge relay system of serine proteases.