Kinetics and Mechanisms of the Photo-Induced Oxidation of Ascorbic Acid by Molecular Oxygen Catalyzed by Ruthenium(II) Complexes Containing 2,2'-Bipyridine and 2,2'-Bipyrazine

Article abstract of DOI:10.1246/bcsj.64.908

Hydrogen peroxide was efficiently produced by the irradiation of visible light on aqueous acid solutions containing ascorbic acid, molecular oxygen, and ruthenium(II) complexes: (2+) (x=0-3, bpy=2,2'-bipyridine, and bpz=2,2'-bipyrazine).The formation of hydrogen peroxide and the decay of ascorbic acid were followed by polarography during continuous irradiation by visible light of the solution.The rate constants of the quenching reaction of the excited triplet state of the ruthenium(II) complexes by ascorbate and molecular oxygen obtained from the initial rate method were in good agreement with those obtained from luminescence quenching experiments.The initiation reaction in the photo-induced reaction mechanism changes from the oxidative quenching of *(2+) by molecular oxygen to the reductive quenching of *(2+), *(2+), or *(2+) by ascorbate.Such a change in the mechanism arises from a difference in the redox potentials, E⁰(Ru(3+)/*Ru(2+)) and E⁰(*Ru(2+)/Ru(+)), for each ruthenium(II) species containing bpy and bpz.The detailed mechanisms are discussed.