Catalytic Olefin Epoxidation with H2O2 in Supercritical CO2. Synergic Effect by hexafluoroacetone and manganese-porphyrins

The heterogeneous oxidation of cyclooctene with hydrogen peroxide catalyzed by manganese 5,10,15,20-tetrakis(2’,6’-dichlorophenyl)porphyrinate, in the presence of hexafluoroacetone hydrate as co-catalyst, has been studied in supercritical carbon dioxide, at 40 oC and 20 MPa. Under proper conditions, a complete olefin conversion may be obtained with the formation of cyclooctene oxide as the sole product. Fixation by hexafluoroacetone into its perhydrate derivatives provides a useful system to solubilize hydrogen peroxide in supercritical carbon dioxide, and to hamper catalyst bleaching and oxidant decomposition. Moreover, in the presence of both manganese-porphyrin and hexafluoroacetone, the reaction rates are enhanced. Among the factors that may increase yields and rate of conversion, the use of a Teflon-coated steel reactor rather than an uncoated one proved to be quite relevant, thus indicating the occurrence of a parasite radical decomposition of hydrogen peroxide promoted by steel reactor walls.