Alkene epoxidation in fluorinated alcohol

The first reports on the use of fluorinated alcohols, and in particular of HFIP in oxidations with hydrogen peroxide, can be found in the patent hterature of the late 1970s and early 1980s [19,20]. Typically, 60% aqueous hydrogen peroxide was used in the presence of metal catalysts. A number of reports on alkene epoxidations in fluorinated alcohols, both in the absence and in the presence of additional catalysts, have followed. 

In 2000, Neimann and Neumann reported on alkene epoxidation by H2O2 in fluorinated alcohol solvents without the addition of further catalysts [21]. Shortly thereafter, in 2001, Sheldon et al. reported about their results, also on alkene epoxidation in fluorinated alcohol solvents [22]. In the latter study, it became clear that buffering the reaction mixtures, preferably by addition of Na2H PO4 improves the overall efficiency of the process, presumably by suppressing acidotalyzed degradation of the product epoxides. Scheme 4.3 summarizes the results obtained using TFE as solvent, whereas the results for HFIP are summarized in Scheme 4.4. 

The catalysts applied to alkene epoxidation in fluorinated alcohol solvents can be subdivided into those which are metal/chalconide-based and those which are purely organic in nature (Scheme 4.5). The former comprise arsanes/arsane oxides [27,28], arsonic acids [29, 30], seleninic acids/diselenides ]31-35], and rhenium compounds such as Re207 and MTO (methylrhenium trioxide) ]36,37]. As shown in Scheme 4.5, their catalytic activity is ascribed to the intermediate formation of, for example, perseleninic/perarsonic adds or bisperoxorhenium complexes. In other words, their catalytic effect is due to the equilibrium transformation of hydrogen peroxide to kmetically more active peroxidic spedes. 

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