Mechanistic investigations of the reaction of an iron(III) octa-anionic porphyrin complex with hydrogen peroxide and the catalyzed oxidation of diammonium-2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate).

A detailed study of the effect of pH, temperature, and pressure on the reaction of hydrogen peroxide with [FeIII(P8−)]7−, where P8− represents the octa anionic porphyrin, was performed using stopped-flow techniques. Depending on the pH, different high valent iron-oxo species were formed. At pH 9 only the one electron oxidized species [(porphyrin)FeIV=O] was found to be present in solution. Under selected conditions at pH 8 it was possible to determine rate constants for both the coordination of hydrogen peroxide and subsequent heterolytic cleavage of the O−O bond. At pH 11 a composite rate constant for coordination of H2O2 and homolytic cleavage of the O−O bond could be measured. In addition, it was possible to determine the activation parameters for the overall reaction sequence leading to the formation of [(porphyrin)FeIV=O]. Careful analysis of the obtained data supports an associatively activated ...