Photocatalytic reduction of phenacyl halides by 9,10-dihydro-10-methylacridine. Control between the reductive and oxidative quenching pathways of tris(bipyridine)ruthenium complex utilizing an acid catalysis

The photoreductions of phenacyl halide derivatives [YC₆H₄COCH₂X (X = Br, Cl; Y = p-CN, p-Br, H, p-Me, p-MeO)] by 9,10-dihydro-10-methylacridine (AcrH₂) in both the absence and presence of perchloric acid in acetonitrile proceed efficiently under irradiation of visible light of λ = 450 nm at 298 K with [Ru(bpy)₃]²⁺ (bpy = 2,2′-bipyridine) as a photocatalyst to yield 10-methylacridinium ion (AcrH⁺) and the corresponding acetophenone derivatives. The dependences of the quantum yields for the [Ru(bpy)₃]²⁺-sensitized photoreduction of phenacyl halides by AcrH₂ on the HClO₄ concentration have been examined. The reductive and oxidative quenching of the excited state [Ru(bpy)₃]²⁺* by AcrH₂ and phenacyl halides in the absence and presence of HClO₄ have also been studied, respectively. The results indicate that the reaction in the absence of HClO₄ proceeds via the reductive quenching of [Ru(bpy)₃]²⁺ by AcrH₂, followed by the reduction of phenacyl halides by [Ru(bpy)₃]⁺, while the reaction in the strongly acidic media proceeds via the oxidative quenching of [Ru(bpy)₃]²⁺ by phenacyl halides, followed by the oxidation of AcrH₂ by [Ru(bpy)₃]³⁺.