The stoichiometry and rate of oxidation with dioxygen of tetra-(p-sulfonatophenyl)-porphinatomanganese(II) and the bisimidazole tetra(p-sulfonatophenyl)porphinato-iron(II) were studied in aqueous solutions at neutral pH. The stoichiometry for both complexes was determined; two molecules of metalloporphyrin reacted with dioxygen to produce the +3 oxidation state of the metalloporphyrins and hydrogen peroxide. The rate law for the oxidation of Mn(II)-TPPS is rate = k′Mn(II)-TPPS]O2], with k′ at 26.5° of 2.6 × 105 M?1 sec?1. The rate law for the oxidation of Fe(II)-TPPS in the presence of imidazole is
