Biphasic catalysis epoxidation

The oxidation of hydrocarbon compounds in aqueous hydrogen peroxide, without added organic solvent (triphase catalysis solid TS-1 + two immiscible liquids) has been found to be faster than in organic solution (biphase catalysis solid TS-1 -I- one liquid). Similarly, the initial rate of epoxidation of propylene was also the highest when conducted in totally aqueous hydrogen peroxide (M. G. Clerici, unpublished results). 

The possibility of asymmetric induction under the fluorous biphase conditions was first speculated upon by Horvath and Rabai [10], and this year has seen the first report of asymmetric catalysis in a fluorous biphase [69]. Two, C2 symmetric salen ligands (29a, b) with four C8Fi7 ponytails have been prepared (Scheme 5) and their Mn(II) complexes evaluated as chiral catalysts for the aerobic oxidation of alkenes under FBS-modified Mukaiyama conditions. Both complexes are active catalysts (isolated yields of epoxides up to 85%) under unusually low catalyst loadings (1.5% cf. the usual 12%). Although catalyst recovery and re-use was demonstrated, low enantioselectivities were observed in most cases. 

S. E. Jacobsen, F. Mares, P. M. Zambri, Biphase and triphase catalysis. Arsonated polystyrenes as catalysts for epoxidation of olefins by aqueous hydrogen peroxide, J. Am. Chem. Soc. 101 (1979) 6946. 

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... 

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