Kinetics and mechanism of the hydrogen peroxide oxidation of a pentafluorophenyl-substituted iron(III) porphyrin†
Abstract
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˙+)FeIVO] formed in the first and rate-limiting step. A second-order rate constant for oxidation of the catalyst of 22 ± 5 dm3 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)FeIVO, probably via the oxoperferryl species. This oxoferryl compound is itself bleached by H2O2 with a second-order rate constant of 0.081 ± 0.004 dm3 mol–1 s–1 probably involving oxidation of the porphyrin ring.