Acetone, a substrate and a new solvent in decatungstate photocatalysis

It is shown that acetone may accompany acetonitrile and water in the very restricted category of conventional solvents for polyoxometalates and more specially decatungstate photocatalyzed reactions. The values of the lifetime, rate constant for inherent decay, and quantum yield for formation of the reactive wO transient in both solvents are practically identical. The only differences relate: (i) to the reactivity of acetone toward wO which is three to four times higher than that of acetonitrile, but remains relatively weak compared to the less reactive substrates, such as alkanes and (ii) to the fact that, in contrast to acetonitrile, no solvated ions have been detected in solutions of decatungstate in acetone by ESMS, thus excluding strong precomplexation. The relative values of the rate constants of reaction of wO with propan-2-ol in acetone, acetonitrile, and water are 1/1.8/23, respectively. This first solvent effect study is consistent with the oxyradical-like character of the reactive transient wO due to the presence of an electron-deficient oxygen center.

It is shown that, in addition to acetonitrile (AN) and water, acetone (AC) may be used as solvent in decatungstate photocatalysis even if its reactivity towards the transient wO is ∼3–4 times higher than that of AC. Additionally, a significant solvent effect is observed in the decatungstate photocatalyzed oxygenation of propan-2-ol: the reactivity of wO is slightly lower in AC than in AN (factor 1.8), but much more important in water. Figure optionsDownload as PowerPoint slide