OXYGEN-TRANSFER REACTIONS .3. THE OXIDATION OF SULFIDES BY SODIUM PERRRUTHENATE

The transfer of oxygen from transition metal oxidants to sulfur (MO(4)(-) + R(2)S --> MO(3)(-) + R(2)SO) has been studied using the oxidation of alkylthio or arylthioacetic acids (RSCH(2)CO(2)H) by perruthenate as models. These reactions exhibit a first-order dependence on the concentrations of both the oxidant and the reductant, and are directly proportional to the basicity of the medium. The Hammet rho value is negative (rho = -0.66), a better correlation being obtained when sigma, rather than sigma(+), substituent constants are used. The entropies of activation for the reactions are large and negative, indicating that the transition state is highly structured. A reaction mechanism involving an activating expansion of the ruthenium coordination shell through incorporation of a hydroxide ion is proposed. Oxygen transfer is then initiated by reaction of a nonbonding pair of sulfur electrons with either a vacant ruthenium d-orbital or a Ru=O pi*-orbital.