Activation Parameters of Bromoacetate–Thiosulfate Reaction in Ethylene Glycol–Water Mixtures

Abstract

The activation parameters for the reaction between bromoacetate (\barR) and S2O32− ions in water and aqueous mixtures of ethylene glycol (5–50% by weight) have been evaluated from the rate constants, corresponding to zero ionic strength, at 15, 25, and 35 °C. The standard free energies of transfer (ΔGtr°) of the reacting ions and hence of the transition state (ΔGtr#) from water to the mixed media at 25 °C have been determined from the measured solubilities of AgR, TlCl, and Tl2S2O3 in the different media, using the reported values of ΔGtr° of Ag+ and Cl− ions. Attempts have been made to interpret the kinetic results in the light of solvent properties and free energies of transfer. Although both the reacting ions are destabilized, on adding glycol to the medium, the larger destabilization of the transition state, arising from decreased dielectric constant as well as solvating capacity of the medium, outweighs the combined effects on the reactants leading to reduced reaction rates.