Mechanism of Water Oxidation by Ferrate(VI) at pH 7-9

The kinetics of water oxidation by K₂ FeO₄ has been reinvestigated by UV/Vis spectrophotometry from pH 7-9 in 0.2 m phosphate buffer. The rate of reaction was found to be second-order in both [FeO₄ ^2- ] and [H⁺ ]. These results are consistent with a proposed mechanism in which the first step involves the initial equilibrium protonation of FeO₄ ^2- to give FeO₃ (OH)^- , which then undergoes rate-limiting O-O bond formation. Analysis of the O₂ isotopic composition for the reaction in H₂ ¹⁸ O suggests that the predominant pathway for water oxidation by ferrate is intramolecular O-O coupling. DFT calculations have also been performed, which support the proposed mechanism.