The Fenton Reaction. Dependence of the Rate on pH

The pH dependence of the evolution of O 2 in the Fenton reaction has been studied by using an indirect method for measuring [O 2 ]. The results confirmed observations of previous workers, namely, that the evolution of O 2 diminished as the pH was lowered. A quantitative analysis of the dependence of [O 2 ] and [Fe 2+ ] during the reaction as a function of time showed that the pH dependence of the course of the reaction can be accounted for by assuming an acid base reaction of the active intermediate: FeO 2+ + H + ⇌ FeOH 3+ . FeOH 3+ is the active entity in the reaction with Fe 2+ to produce Fe 3+ ions, while the other form FeO 2+ is involved in reactions leading to O 2 evolution.