KINETICS, MEDIUM, AND DEUTERIUM ISOTOPE EFFECTS IN THE ALKALINE DECOMPOSITION OF QUATERNARY PHOSPHONIUM SALTS III1Tetraphenylphosphonium Chloride in Dimethylsulphoxide-Water Mixtures

Abstract

Abstract The reaction between tetraphenylphosphonium chloride and hydroxide or deuteroxide anions was studied kinetically in a series of dimethylsulphoxide-water mixtures at several temperatures. The rate is first-order in the phosphonium cation and second-order in the hydroxide or deuteroxide anions. The reaction shows a dramatic increase in rate, up to about 1010 times, as the DMSO content is increased. The rate enhancement is attributed to a considerable drop in activation energy affected not only through an increased desolvation of reactant anions, but also through an increase in solvation of the transition state, brought about by gradual addition of DMSO. The kinetic solvent deuterium isotope effect in 60% DMSO-40% D2O is strongly dependent on temperature. The rate constant in the latter solvent mixture is represented by k i = 11.9 e −12700/RT l 2 mole−2 sec−1 as compared to k i = 19.0 e −22500/RT l 2 mole−2 sec−1 in the corresponding 60% DMSO-H2O mixture. The thermodynamic parameters of activation s...