Mild catalytic oxidations of unsaturated fatty acid methyl esters (FAMEs) by oxovanadium complexes

A selection of unsaturated fatty acid methyl esters, namely methyl oleate (C18:1), methyl linoleate (C18:2) and methyl linolenate (C18:3) has been oxidized under mild homogeneous catalytic conditions, using a series of oxovanadium(IV) complexes containing 4-acyl-5-pyrazolone donor ligands with different substituents on acyl residue. The main goal was to evaluate the catalytic role exerted by oxovanadium(IV) metal center, as precursor complex, in the selective oxyfunctionalization of carbon-carbon double bonds of these bio-renewable resources, as a greener alternative to more drastic processes currently used at the industrial level. The three substrates, oxidized using tert-butylhydroperoxide as main oxidant, with or without solvents, showed high conversions of starting materials and high selectivities in the formation of corresponding mono- di- and tri-epoxides, especially under solvent-less conditions. Investigations on a probable catalytic cycle mechanism operative in the tert-butylhydroperoxide oxidation of a simple FAME model substrate, have been performed by means of ESI-MS.