Anchoring of vanadyl acetylacetonate onto amine-functionalised activated carbons: Catalytic activity in the epoxidation of an allylic alcohol

Vanadyl(IV) acetylacetonate was anchored onto two different amine-functionalised activated carbons. The starting activated carbon supports were air (A2) and nitric acid oxidised (131) carbons; the phenol surface groups of carbon A2 were subsequently treated with (3-aminopropyl)triethoxysilane (A3) and afterwards the free amine groups were used for Schiff condensation with [VO(acac)(2)] (A4). Carbon B1, which possesses carboxylic surface groups, was treated with thionyl chloride to give surface acyl chloride groups (132), which were then reacted with the amine groups of bis(3-aminopropyl)amine (133); subsequent attachment of [VO(acaC)(2)] was also achieved by Schiff condensation between the free amine groups of the functionalised carbon and the ligand oxygen atoms (B4). All the materials were characterised by XPS, and the [VO(acaC)(2)]-based materials were also characterised by vanadium elemental analysis and EPR spectroscopy. A combination of all the data provides evidence for the covalent attachment of the vanadium complex onto the modified activated carbons. The catalytic activity of the [VO(acaC)2]-based materials in the epoxidation of 3-buten-2-ol using tert-butyl hydroperoxide as oxygen source was assessed and compared to that of the homogeneous phase reaction. The alkene conversion in the heterogeneous phase is similar to that observed in the homogeneous phase, although the rate of oxidation is less than half that of the homogeneous system. Material A4 exhibits higher catalytic efficiency than B4; upon reuse, both materials show no significant decrease in their catalytic properties. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.