Investigation of the catalytic behavior of ion-pair complexes of vanadium(V) in the liquid-phase oxidation of hydrocarbons with molecular O2

Ion-pair complexes of decavanadate were prepared with different cationic phase-transfer catalysts (PTCs) and their catalytic behavior was investigated in the oxidations of tetralin and cyclohexene with molecular O-2. It was found that both the PTCs themselves and their ion-pair complexes enhanced the rate of oxidation. The catalytic activities of both the PTCs and their ion-pair complexes depend strongly on their concentrations. At low concentrations (< 10(-3) M), the PTCs themselves (in the form of spherical inverse micelles) proved to be the more active but at higher concentrations where the growing micelles are transformed into a more open layer structure, the ion-pair complexes exerted the higher catalytic activities. At concentrations near 0.1 M the efficiencies of both types of catalysts decreased because the layers start to transform into a more closed micellar structure. The structure of the micelles is also influenced by the pH of the aqueous phase used during the preparation of the catalyst solutions. (C) 2000 Elsevier Science B.V. All rights reserved.