On the oxidation of organic sulphoxides by potassium t-butyl peroxide

Abstract

The kinetics of the oxidation of some representative organic sulphoxides (to the corresponding sulphones) by potassium t-butyl peroxide in toluene have been studied in the presence of crown polyethers. A two-step reaction mechanism involving preliminary nucleophilic attack by the peroxide on the sulphoxide, followed by the breakdown of the reactive intermediate thus formed via heterolysis of the O–O bond is envisaged. Addition of the protic species Bu^tOH and PrⁱOH in large excess over the reactants depresses the rates. However, with initial concentrations of Ph₂SO and Bu^tOOK of ca. 5 × 10^–2 and 0.5 × 10^–2M, respectively, addition of up to ca. 10^–2M-Bu^tOH is observed to enhance the rate. On changing the alcohol from Bu^tOH to PrⁱOH, and the substrate from Ph₂SO to (p-MeOC₆H₄)₂SO, to Me₂SO, the variation k_2,obs. with alcohol concentration follows a trend which depends on the nature of the alcohol and on structure of the sulphoxide. This yields useful information on the reaction mechanism.