Kinetics of ligand-substitution in glycerol at high pressures, by a laser temperature-jump method

Abstract

The kinetics of the reactions of the ligand pyridine-2-azo-p-dimethylaniline with Co^II, Ni^II, Cu^II and Zn^II ions in glycerol have been studied, at pressures up to 2760 b over a range of temperatures. Activation enthalpies and volumes are reported for Co^II and Zn^II. The rate constants for the four cations at 1 b and 20°C are the same within a factor of 4; they are smaller than the value calculated for diffusion control, by a factor of 10² to 10³. The activation enthalpies for Co^II and Zn^II are close to that expected for diffusion control. The activation volume for Zn^II is fairly close to the diffusion-controlled value, but that for Co^II is smaller. The results are discussed in relation to a model which takes into account diffusion, steric factors and ring closure.