Kinetics and mechanism of the hydrogen peroxide oxidation of a pentafluorophenyl-substituted iron(III) porphyrin

Kinetic analysis of the (F20TPP)FeCl-catalysed H2O2 oxidation of 3-hydroxy-2-(trans-4-tert-butylcyclohexyl)methylnaphtho-1,4-quinone is consistent with rapid reaction of the organic substrate with an oxoperferryl intermediate [(F20TPP.+)Fe-IV=O] formed in the first and rate-limiting step. A second-order rate constant for oxidation of the catalyst of 22 +/- 5 dm(3) mol(-1) s(-1) is found, a value lower than previously reported. In the absence of the organic substrate, H2O2 oxidises the catalyst to an oxoferryl species (F20TPP)Fe-IV=O, probably via the oxoperferryl species. This oxoferryl compound is itself bleached by H2O2 with a second-order rate constant of 0.081 +/- 0.004 dm(3) mol(-1) s(-1) probably involving oxidation of the porphyrin ring.