Kinetics of oxidation of para-substituted phenyl methyl sulphides by pyridinium chlorochromate in dipolar protic and aprotic solvents
Abstract
The kinetics of oxidation of phenyl methyl sulphide (PMS) and several para-substituted phenyl methyl sulphides by pyridinium chlorochromate have been studied in binary solvent mixtures of 60%(v/v) aqueous acetic acid and 50%(v/v) chlorobenzene–nitrobenzene. Acrylonitrile has no effect on the rates of oxidation. In aqueous acetic acid, there is overall second-order reaction. The Hammett p value of –2.12 ± 0.09 (r 0.985, s 0.104) at 50 °C indicates an electron-deficient transition state. In chlorobenzene–nitrobenzene there is an association equilibrium prior to the rate-limiting step, follwed by irreversible decomposition of the complex into products. The complex formation constants (K) and the complex decomposition of rate constants (k1) have been computed from the double reciprocal plots of 1/Kobsversus 1/[PMS]0. The decomposition rate constants (k1) correlate well with Hammett σ values (p–1.23 ± 0.054, r 0.989,s 0.068 at 50 °C). On the basis of the results of the kinetic studies, a suitable mechanism has been proposed.