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)

Abstract

The rate of the oxidation reaction of the oxalate ion to carbon dioxide by the peroxodisulphate ion (S₂O₈^2–) 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 S₂O₈^2–. 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 k_q 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⁺+ S₂O₈^2– [graphic omitted] [Ru(bipy)₃]³⁺+ SO₄˙^–+ SO₄^2–(ii), C₂O₄^2–+ SO₄˙^–→ CO₂˙^–+ CO₂+ SO₄^2–(iii), [Ru(bipy)₃]³⁺+ CO₂˙^–→[Ru(bipy)₃]²⁺+ CO₂(iv), SO₄˙^–+ CO₂˙^–→ SO₄^2–+ CO₂(v), –d[S₂O₈^2–]/dt=k_qI_aΦ[S₂O₈^2–]//_{k0+kq[S2O8^2–]}(vi)