Investigation of the catalytic behavior of ion-pair complexes of vanadium(V) in the liquid-phase oxidation of hydrocarbons with molecular O-2

Ion-pair complexes of decavanadate were prepared with different cationic ph ase-transfer catalysts (PTCs) and their catalytic behavior was investigated in the oxidations of tetralin and cyclohexene with molecular O-2. It was f ound that both the PTCs themselves and their ion-pair complexes enhanced th e rate of oxidation. The catalytic activities of both the PTCs and their io n-pair complexes depend strongly on their concentrations. At low concentrat ions (< 10(-3) M), the PTCs themselves (in the form of spherical inverse mi celles) 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 th e layers start to transform into a more closed micellar structure. The stru cture of the micelles is also influenced by the pH of the aqueous phase use d during the preparation of the catalyst solutions. (C) 2000 Elsevier Scien ce B.V. All rights reserved.