Polyoxometalates catalysts in the oxidation of cyclooctane by hydrogen peroxide

Abstract

A Keggin-type tungstocobaltate, [Co(2,2'- bipy)3]2H2[CoW12O40]?9.5H2O ([Co]CoW) and tetrabutylammonium salt of vanadium-substituted tungstophosphates [(n-C4H9)4N]4[PVW11O40], [(n-C4H9)4N]5[PV2W10O40] (PVW, PV2W) were used as catalyst for oxidation of cyclooctane with H2O2 as oxidant in acetonitrile. The activity of [(n-C4H9)4N4H[PCo(H2O)W11O39]?2H2O (PCoW) was also compared. The products of the reaction were cyclooctanone, cyclooctanol and cyclooctyl hydroperoxide. The experimental results showed that at H2O2/cyclooctane molar ratio = 3 at 80?C, in 9 h the [Co]CoW yielded higher conversion and selectivity to cyclooctanone. The V-based catalysts are more active than the Co-based tungstophosphate. The PV2W gave rise to high selectivity to cyclooctyl hydroperoxide. Cyclooctane conversion was increased by increasing reaction time or H2O2/cyclooctane molar ratio. In the presence of tungstocobaltate catalyst, 88% cyclooctane conversion and 82% selectivity of cyclooctanone were obtained after 12 h using H2O2/cyclooctane molar ratio of 9. This catalyst is stable upon treatment with H2O2. Experiments with radical traps suggest the involvement of a free-radical mechanism.