Abstract
The photochemical excitation of aqueous solutions of Ru(bpy)32+ and phenol (PhOH) in the presence of air produces 1,4-benzoquinone (BQ) as the only organic product. In this study, we examined the *Ru(bpy)32+/PhOH/O2 system in terms of the dependence of the quantum yield of BQ formation (ΦBQ) as a function of [O2], [PhOH], temperature, pH, and the composition of the solvent. The increase in ΦBQ from its low value in acidic solution to its maximum at pH ∼ 9.4 is attributed to the increasingly competitive quenching of *Ru(bpy)32+ by PhO- and O2. A maximum in ΦBQ is also observed at ∼45 °C, an effect caused by the variation in the solubility of O2 in solution as well as the activation energies of the competing steps in the mechanism. The proposed mechanism of the reaction, which could involve the formation of an endoperoxide intermediate from the reaction of 1O2 by PhOH, is consistent with the observed decrease of ΦBQ as a function of the mole fraction of H2O in CH3CN−H2O solvent mixtures.
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