Polyoxometalate catalysts in the oxidation of cyclooctane by hydrogen peroxide

Abstract

A Keggin-type tungstocobaltate, [Co(2,2'-bipy)3] 2H2[CoW12O40]·9.5H 2O ([Co]CoW) and tetrabutylammonium salt of vanadium-substituted tungstophosphates [(n-C4H9)4N] 4[PVW11O40], [(n-C4H 9)4N]5[PV2W10O 40] (PVW, PV2W) were used as catalysts for the oxidation of cyclooctane with H2O2 as the oxidant in acetonitrile. The activity of [(n-C4H9)4N 4H[PCo(H2O) W11O39]·2H 2O (PCoW) was also compared. The products of the reaction were cyclooctanone, cyclooctanol and cyclooctyl hydroperoxide. The experimental results showed that at an H2O2/cyclooctane molar ratio of 3 at 80 °C, [Co]CoW yielded a higher conversion and selectivity to cyclooctanone in 9 h. The V-based catalysts were more active than the Co-based tungstophosphate. PV2W gave rise to high selectivity to cyclooctyl hydroperoxide. Cyclooctane conversion was increased by increasing the 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 an H2O2/cyclooctane molar ratio of 9. This catalyst is stable upon treatment with H2O2. Experiments with radical traps suggested the involvement of a free-radical mechanism. Copyright © 2012 (CC) SCS.