Fluorous solvents epoxidation

Table 6.10 MTO-catalyzed epoxidation of olefins with anhydrous H2O2 or with aqueous H2O2 in fluorous solvents.131...

Further efficient ligands for the epoxidation of alkenes have been reported by Pozzi, but using PhIO as the oxidant and pyridine V-oxide as an additive in FBS.[7, 51-53] Chiral (salen)Mn complexes have been synthesised, which are soluble in fluorous solvents and active in the epoxidation of a variety of alkenes. The catalysts were of the form shown in Figure 6.14. 

Fluorous solvents proved to be highly effective in epoxidation of alkenes. H202 can be used in combination with trifluoroacetone,27 perfluoroacetone,28 or a mixture of perfluoroacetone and hexafluoro-2-propanol.29 In fluorinated alcohols as solvents uncatalyzed epoxidations with aqueous H202 are performed.30,31... 

In this context it is interesting to note the recent reports of fluorous catalysis without fluorous solvents [68]. The thermomorphic fluorous phosphines, P[(CH2)m(CF2)7CF3]3 (m=2 or 3) exhibit ca. 600-fold increase in n-octane solubility between -20 and 80 °C. They catalyze the addition of alcohols to methyl propiolate in a monophasic system at 65 °C and can be recovered by precipitation on cooling (Fig. 7.20) [68]. Similarly, perfluoroheptadecan-9-one catalyzed the epoxidation of olefins with hydrogen peroxide in e.g. ethyl acetate as solvent [69]. The catalyst could be recovered by cooling the reaction mixture, which resulted in its precipitation. 

Epoxidation. Cooxidation of alkenes and pivalaldehyde with oxygen in fluorous solvents has been effected by Mn(0Ac)j-2H20. 

Except for transitions from heterogeneous to homogeneous catalysis, there is also common groimd for the various methodologies described here the application of SCCO2 is described in the presence of ionic liquids [32a] or of fluorous solvents [32b,c] as well in aqueous operation [33a-d] and aerobic epoxidations have been attained in fluorous biphasic systems using ionic liquids [33e]. On the other hand, ionic liquids [34] or fluorous solvents [35a,c] have been used together with aqueous operations and water-soluble polymers are the focal point of the application of... 

Table 2.7 MTO-catalyzed epoxidation of alkenes with H2O2, anhydrous or in fluorous solvents. ...

At ambient temperature and pressure, hexafluoroacetone is a (toxic) gas, and catalyst recovery is impractical. As a nonvolatile alternative, Sheldon et cd. employed perfluoroheptadecan-9-one. After completion of the epoxidation, this catalyst can be recovered from halogenated solvents such as dichloroethane or TFE by simple cooling of the reaction mixture [39]. Furthermore, this long-chain perfluorinated ketone has the potential for immobilization in fluorous phases. When appHed to epoxidation with perfluoroheptadecan-9-one as catalyst, TFE gave yields of epoxide comparable to those obtained in dichloroethane. However, to achieve good yields of add-sensitive epoxides, buffering by Na2HP04 was necessary. 

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