Oxidation of Ru(III)-Bound Thiocyanate with Peroxomonosulfate: Kinetic and Mechanistic Studies

The reaction of [RuIII(edta)(SCN)]2− (edta4− = ethylenediaminetetraacetate; SCN− = thiocyanate ion) with the peroxomonosulfate ion (HSO5−) has been studied by using stopped-flow and rapid scan spectrophotometry as a function of [RuIII(edta)], [HSO5−], and temperature (15–30oC) at constant pH 6.2 (phosphate buffer). Spectral analyses and kinetic data are suggestive of a pathway in which HSO5− effects the oxidation of the coordinated SCN− by its direct attack at the S-atom (of SCN−) coordinated to the RuIII(edta). The high negative value of entropy of activation (ΔS≠ = −90 ± 6 J mol−1 deg−1) is consistent with the values reported for the oxygen atom transfer process involving heterolytic cleavage of the O-O bond in HSO5−. Formation of SO42−, SO32−, and OCN− was identified as oxidation products in ESI-MS experiments. A detailed mechanism in agreement with the spectral and kinetic data is presented.