New eco-friendly one-pot tandem synthesis of cyclic organic carbonates from oleochemicals

In the present work a new methodology has been developed for the stereo-controlled direct oxidative carboxylation of unsaturated fatty acids methyl esters (FAMEs, especially methyl oleate) into internal cyclic carbonates with carbon dioxide. The synthesis is composed by two main steps: an epoxidation of the starting unsaturated FAME followed by the CO2 fixation into the epoxide, both catalyzed by tungstate-based ionic liquids. The initial solvent-free epoxidation takes place in a two-phase system with hydrogen peroxide as oxidant with the tungstate-based ionic liquids acting as H2O2 activators and phase-transfer catalysts. The second step, -CO2 fixation- occurs under CO2 pressure, with the addition of a halide source as co-catalyst. Both reactions have been investigated over different parameters and the reaction conditions were carefully optimized. A maximum yield of 70% was obtained. Finally, the protocol’s suitability to other substates was tested, with emphasis on oleic acid and methyl linoleate.