Kinetics of hydrolysis of some N′-(4-substituted benzylidene) salicylohydrazides

Abstract

The rates of hydrolysis of a series of substituted benzylidenesalicylohydrazide derivatives in 40%(v/v) ethanol–buffer mixture have been investigated by differential pulse polarography. The hydrolysis is catalysed by H⁺ and its rate follows strictly first-order kinetics. The rate constant decreases with increasing pH up to around pH 3.9, beyond which no measurable reaction was observed; here the protonation of imine begins to be significantly incomplete. The attack of water on the protonated substrate is considered to be the rate-determining step. The effects of pH, molecular structure, and temperature on the reaction rate and the activation energy are reported. Thermodynamic parameters (ΔG^‡, ΔH^‡, and ΔS^‡) for the hydrolysis are discussed.