Abstract
Ionic liquid (IL), such as 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), as an activator for the epoxidation of a wide variety of olefins with H2O2 catalyzed by Keggin polyoxometalate [bmim]3PW12O40 has been demonstrated. Use of IL results both in significant enhancement of TOF and selectivity for olefin epoxidation compared to that of traditional organic solvents, e.g. 289 times TOF and 1.3 times selectivity as found in CH2Cl2 for the epoxidation of cis-cyclooctene. The kinetic 31P NMR spectra uncover that the active peroxotungstate [PO4{W(O)(O)2}4]3− (Venturello complex), contributing to the epoxidation, can be readily generated in the presence of [bmim][PF6]. Furthermore, the counterion such as PF6− and [(CF3SO2)2N]− is evidenced to play a crucial role in the epoxidation of olefin. BF4− as counterion, instead of PF6−, is found to reduce TOF and selectivity for cis-cyclooctene epoxidation dramatically from 289 to less than 1 and from 99% to 12%, respectively.
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