Mechanisms of oxidation reactions of iodide and hexacyanoferrate(II) ions, induced by the reaction between phosphinate ion and molecular oxygen in an aqueous solution

When an I- solution was mixed with a PH2O2- solution which had been kept standing for given times of 5-40 min in the presence of molecular oxygen (O-2), the I-2 (or I-3(-)) was rapidly formed and then gradually reduced. The maximum amounts of the formed I-2 (or I-3(-)) increased with increasing standing times of the PH2O2- solution, and with increasing concentrations of PH2O2- and H+ in the solution. When the [Fe(CN)(6)](4-) solution was mixed with the PH2O2- solution, [Fe(CN)(5)](3-) was formed quantitatively, but an induction period appeared under the conditions of low concentrations of PH2O2- and high pH's. The induction period was shortened at higher concentrations of PH2O2-, O-2, and/or H+. Both oxidation reactions of I- and [Fe(CN)6]4- were extremely accelerated by the addition of small amounts of the peroxodiphosphate salt (K4P2O8) into the solution, both were inhibited by the presence of radical scavengers, and never occurred in the N-2-saturated solution. The mechanisms for such O-2-induced/radical reactions, which are regarded as a new type of Fenton-like reagent, are discussed.