Selective oxidation of saturated hydrocarbons catalyzed by oxovanadium(iv) complexes

Abstract

The development of the selective oxidation of saturated hydrocarbons catalyzed by oxovanadium(IV) complexes was disclosed. Two types of ligands including Schiff’s base and picolinic acid could be prepared. The well-characterized oxovanadium(IV) complexes were applied under two diverse oxidizing agents: O2 and peroxide. The oxidation catalyzed by oxovanadium(IV) Schiff’s base complexes in zinc-pyridine-acetic acid system under O2 was thoroughly investigated for the effects of nine Schiff’s base complexes, amount and type of zinc, acid and solvent. VO(salophen) exhibited good activity in terms of yield of desired product(s) and selectivity. Utilizing this catalyst in combination with TBHP at reflux or H2O2 at room temperature in CH3CN could promote the selective oxidation reaction. These three catalytic systems revealed the unique characteristics for ketone formation as a major product together with small amount of accompanying alcohol. Employing VO(pic)2 in TBHP system, saturated hydrocarbons were oxidized faster than using VO(salophen) and still provided ketone as predominant product in good yield. The addition of hexabromoacetone (HBA) converted the activation process to furnish alkyl bromide efficiently instead of oxidized products. Chemoselectivity study implied the clues that reaction mechanisms of two systems were different. Non-radical pathway was operated in zinc-pyridine-acetic acid-O2 system while for peroxide system, the oxidation proceeded via radical process.