Light-induced electron-transfer reactions. Part 3. Kinetics of the oxidation reaction of oxalate ion by peroxidisulphate ion, induced by irradiation with visible light of an aqueous solution containing tris(2,2′-bipyridine)ruthenium(II)
The rate of the oxidation reaction of the oxalate ion to carbon dioxide by the peroxodisulphate ion (S2O82–) is greatly accelerated by irradiation with visible light of aqueous solutions containing tris(2,2′-bipyridine)ruthenium(II) ion, [Ru(bipy)3]2+, as a photo-sensitizer and catalyst. The mechanism constitutes a chain reaction initiated by the reaction between the photo-excited complex [*Ru(bipy)3]2+ and S2O82–. The results are accounted for by a mechanism described by equations (i)–(v). The rate of reaction is given by equation (vi). The mechanism of reaction and the rate law were verified, and the bimolecular quenching constants kq were determined by kinetic experiments under various conditions. [Ru(bipy)3]2++hν[graphic omitted][*Ru(bipy)3]2+ [graphic omitted] [Ru(bipy)3]2++hν′+Δ(i), [*Ru(bipy)3]2++ S2O82– [graphic omitted] [Ru(bipy)3]3++ SO4˙–+ SO42–(ii), C2O42–+ SO4˙–→ CO2˙–+ CO2+ SO42–(iii), [Ru(bipy)3]3++ CO2˙–→[Ru(bipy)3]2++ CO2(iv), SO4˙–+ CO2˙–→ SO42–+ CO2(v), –d[S2O82–]/dt=kqIaΦ[S2O82–]//k0+kq[S2O82–] (vi)