Kinetics of the oxidation of formic acid by aquocerium(IV) ions in aqueous perchlorate media

Abstract

The slow oxidation of formic acid by Ce^IV proceeds by an inner-sphere mechanism. The rate of disappearance of Ce^IV is always of the first order in [Ce^IV], and the pseudo-first-order rate constant k₀ increases sharply with increasing [HCO₂H] to a value independent of [HCO₂H]: in the latter region k₀ is directly proportional to [HClO₄]. This is consistent with the existence of complexes Ce⁴⁺HCO₂H_aq and Ce⁴⁺HCO₂^–_aq with only the former involved in the oxidative step. At very high [HCO₂H] solvent effects and/or the formation of higher complexes cause k₀ to increase again slowly with increasing [HCO₂H].