Kinetics and mechanisms of the oxidation of hypophosphite and phosphite with trans-[RuVI(L)(O)2]2+ (L = 1,12-dimethyl-3,4∶9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane)
Abstract
The kinetics of the oxidation of hypophosphite and phosphite by trans-[Ru(L)(O)2]2+ (L = 1,12-dimethyl-3,4∶9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane) have been studied in aqueous acidic solutions. The reactions have the following stoichiometry (x = 2 or 3): trans-[RuVI(L)(O)2]2+ + H2POx− + ‡ = (60 ± 2) kJ mol−1 and ΔS‡ = (−41 ± 4) J mol−1 K−1 at pH = 1.86 and I = 1.0 mol dm−3. For phosphite, ΔH
‡ = (59 ± 4) kJ mol−1 and ΔS‡ = (−75 ± 13) J K−1 mol−1 at pH = 2.3 and I = 0.2 mol dm−3. Deuterium isotope effects have also been investigated. For hypophosphite, the kinetic isotope effect, k(H2PO2−)/k(D2PO2−) is 4.1 at pH = 1.07 and I = 1.0 mol dm−3. For phosphite, the kinetic isotopic effect, k(HDPO3−)/k(D2PO3−), is 4.0 at pH = 2.30 at I = 0.2 mol dm−3. A mechanism involving
O is proposed for these two reactions.