Kinetics of the Peroxydisulfate Oxidation of Sulfoxides in Buffered Solution. 2. The Effect of Initial Sulfoxide Concentration with Diethyl and Diphenyl Sulfoxides

Article abstract of DOI:10.1021/j150650a032

The kinetics of reduction of 0.02 M K2S2O8 by diethyl and diphenyl sulfoxides in buffered aqueous solution were studied, the concentration of R2SO being varied in each run.The stoichiometric equation is S2O8^2- + 3H2O + R2SO -> 2H3O⁺ + R2SO2 and the corresponding sulfones were isolated as the reaction products from the runs.The kinetics, measured by the rate of persulfate disappearance, followed iodometrically, were first order in any given run, but the first-order rate constants are a marked function of the initial concentration of sulfoxide.The plots of k vs. ₀ are rectangular hyperbolas given by the equation k = k_max0/(b + ₀), where k_max is a limiting rate approached at high sulfoxide concentrations, and b is a constant, equal to that concentration of R2SO for which k = k_max/2.For the oxidation of Et2SO, ΔH^<*> is 27 kcal/mol and ΔS^<*> = -0.4 eu; for Ph2SO, ΔH^<*> = 30 kcal/mol and ΔS^<*> = +6.6 eu.The high activation energy and lack of ESR signals provide evidence that these are not free-radical chain reactions.Five possible mechanisms are considered, one of which is preferred.