Nature of intermediates in the catalytic decomposition of hydrogen peroxide by ferric ions

The structure of the secondary iron(III)-hydrogen peroxide complex (C _II) is investigated on the basis of a previously established ion-pair structure (Fe⁺³HO₂^-) for C_I. Consideration of free radical mechanisms, following a hypothetical reduction of C_I to C_II, shows that such a reduction in the transition C_I→C_II is excluded. No transient change of pH is observed during the decomposition even under circumstances in which C _II accumulates. This indicates that the acid equivalent, formed simultaneously with C_I, disappears upon the formation of C _II. The velocity constant of the transition is independent of pH. It is concluded, therefore, that the process consists of a loss of OH^- ions. C_II is identified as FeO³⁺.