Kinetics and mechanisms of substitution reactions with sulfur‐containing nucleophiles in aqueous acid solutions. I—rates of reactions of some tetrahalopalladate (II) anions with thiourea and selenourea

Abstract

The activation energy parameters for the reaction of P d X P (X = C1-, Br-) in aqueous halide acid solution with thiourea (tu) and selenourea (seu) have been determined. High rates of reaction parallel low enthalpies and appreciable negative entropy of activation.The rate law in each case simplifies to /cobs = k[L] where L = tu or seu, and only liganddependent rate constants are observed at 25°C. The liganddependent rate constants for the first identifiable step in the PdCId2-+ X system is (9.1 f 0.1) X lo3 M-' sec-* and (4.5 & 0.1) X lo4 M-' sec-' for X = tu and seu, respectively, while for the PdBrr2-+ X system it is (2.0 f 0.1) X lo4 M-' sec-' and (9.0 f 0.1) X lo4 M-' sec-' for X = tu and seu, respectively.