| Abstract |
Carbamated silica gel supported bis(maltolato)oxovanadium(IV or V) complexes, [VO(ma)(2)] (1), [VO(py)(ma)(2)] (2) (py=pyridine), cis[VO(OCH3)(ma)(2)] (3) and cis-[VO(OC2H5)(ma)(2)] (4), were used as catalysts for the oxidation of cyclopentane and cyclooctane by molecular oxygen in a batch reactor, under moderate reaction conditions (typically P(O-2) ca. 10-14atm, at 150-160 degrees C). The corresponding ketones, i.e. cyclopentanone and cyclooctanone are the main products (up to 10 and 25\% yields, respectively) of the cycloalkane oxidations, but cyclopentanol and cyclooctanol are also formed in smaller amounts. The supported complex 1 shows the best activity and selectivity. The reaction is further promoted by the use of some heteroaromatic acids as co-catalysts, namely 2-pyrazine-carboxylic acid. Experiments with radical traps suggest the involvement of a free-radical mechanism. (c) 2006 Elsevier B.V. All rights reserved. |
