| Popis: |
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− + H2O → trans-[RuIV(L)(O)(OH2)]2+ + H2POx + 1−. The two reactions have the same rate law (P = hypophosphite or phosphite): −d[RuVI]/dt = k/(1 + [H+]/K)[RuVI][P]. For hypophosphite, k = (1.3 ± 0.1) dm3 mol−1 s−1 and K = (9.7 ± 0.5) × 10−2 mol dm−3 at 298 K and I = 1.0 mol dm−3. For phosphite, k = (4.8 ± 0.4) × 10−2 dm3 mol−1 s−1 and K = (1.2 ± 0.2) × 10−2 mol dm−3 at 298 K and I = 0.2 mol dm−3. The effects of temperature were studied from 15 °C to 40 °C. For hypophosphite, ΔH‡ = (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 hydride transfer from P–H to RuO is proposed for these two reactions. |
