Aerobic photooxidation in water by polyoxotungstates: The case of uracil

Uracil photooxygenation occurs in acidic water (pH = 1) at 25 degrees C, under oxygen (1 atm), irradiating with), lambda > 300 nm in the presence of selected polyoxometalates (POM). A marked diversity of photocatalytic behavior is registered for different PONIs in terms of oxidation rate and selectivity. H3PW12O40 (PW12) appears to be the most reactive photocatalyst, by far superior to isostructural complexes, leading to a product distribution typical of OH center dot dominated oxidations, while Na4W10O32 (W-10) and Na-12[WZn3(H2O)(2)(ZnW9O34)(2)] (Zn5W19) exhibit a preferential reactivity towards uracil glycol. Kinetic studies and radical scavenger probes, performed on target intermediates and model diols, highlight a substantial difference in the mechanism of photocatalysis by the three complexes. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).