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

Thermal behaviour of polyethylene‐block‐poly(methyl methacrylate) block copolymer: effect of multiple heating and cooling ratesversusmathematical artefact

“…The PE-b-PMMA diblock copolymer consists of a semi-crystalline PE hard block and an amorphous PMMA soft block. The crystallization temperatures of linear PEs vary from 118 to 125 ∘ C. 8 -10 In contrast, the glass transition temperature of isotactic PMMA ranges from 53 to 58 ∘ C. 11,12 Therefore, the diblock copolymer of the two components has the features that only the PE block is crystallizable and the corresponding PE crystallization temperature is greater than the PMMA glass transition temperature (soft confinement case). 13 Hence, to study the influence of the PMMA functional soft block on crystallization kinetics (through model and experiment) is both interesting and important.…”

Robust Bio-derived Polyoxometalate Hybrid for Selective Aerobic Oxidation of Benzylic C(sp3)–H Bonds

“…Polyoxometalates (POMs), a class of anionic metal–oxygen clusters, have stimulated broad research interest as efficient catalysts, − especially in diverse oxidation reactions. For the oxidation of C­(sp 3 )–H bonds to form carbonyl compounds, several POMs have been applied, such as [ n -Bu 4 N] 5 [PV 2 Mo 10 O 40 ], [( n -C 4 H 9 ) 4 N] 4 [γ-HPV 2 W 10 O 40 ], K 8 [SiW 11 O 39 ] linked by Fe­(salen), and a POM-incorporated framework . However, these catalytic systems generally used tert -butyl hydroperoxide, H 2 O 2 , or nitrous oxide as the oxidant, ,, which to some extent are expensive, corrosive, or environmentally unbenign.…”