Pulse Radiolytic Studies of the Reactions of HO2/O2- with Fe(II)/Fe(III) Ions. The Reactivity of HO2/O2- with Ferric Ions and Its Implication of the Occurrence of the Haber-Weiss Reaction

Article abstract of DOI:10.1021/j100269a035

The reactions between ferrous ion, Fe²⁺, and the simple complexes of Fe(III), FeOH²⁺, and FeSO4⁺ with superoxide and perhydroxyl radicals O2^-/HO2 have been studied as a function of pH (1-7) in aqueous sulfate and formate media.The measured rate constants for the various reactions are k₁₇(HO2 + Fe²⁺) = (1.2 +/- 0.2) X 10⁶ M^-1 s^-1 (in good agreement with earlier reported values^6d); k₁₈(O2^- + Fe²⁺) = (1.0 +/- 0.1) X 10⁷ M^-1 s^-1; k₂₀(O2^- + FeSO4⁺) ca. k₂₂(O2^- + FeOH²⁺) = (1.5 +/- 0.2) X 10⁸ M^-1 s^-1.The reduction of FeSO4⁺ by HO2 is relatively slow, k₁₉(HO2 + FeSO4⁺) 3 M^-1 s^-1.At neutral pH the superoxide radical is catlytically decomposed to dioxygen and hydrogen peroxide by trace amounts of Fe(II)/Fe(III), if the overall reaction is completed before Fe(III) can polymerize/precipitate.The corresponding second-order rate constant is k_cat = (1.3 +/- 0.2) X 10⁷ M^-1 s^-1.The results from the kinetic studies of reactions 20 and 22 corroborate the mechanism for the catalytic decomposition of hydrogen peroxide by Fe(II)/Fe(III) advanced by Barb, Baxendale, George, and Hargrave in 1951.^2,3