KINETICS OF HYDROLYSIS OF PHENYL ACETATES CATALYZED BY THE ZINC(II) COMPLEX OF 1,5,9-TRIAZACYCLODODECANE - EVIDENCE FOR ATTACK OF WATER OR HYDROXIDE ION AT THE COORDINATED ESTER

Rates for hydrolysis of substituted phenyl acetates were measured in t he presence of the Zn(II) complex of 1,5,9-triazacyclododecane. The ki netic data are incompatible with the mechanism in which the water and hydroxide ion coordinated to the metal center makes a nucleophilic att ack at the ester linkage. Instead, the results support the mechanism i n which the ester is first complexed to the metal center and then wate r or hydroxide ion makes a nucleophilic attack at the complexed ester. The kinetic data further indicate that the electrostatic interaction between the cationic metal center and the anionic hydroxide ion facili tates the attack of hydroxide ion at the complexed ester. In addition, the C-O bond of the ester is not cleaved significantly in the rate-de termining transition state for attack by both water and hydroxide ion.