Abstract
This chapter reviews recent progress made in reaction-controlled phasetransfer catalysis for the epoxidation of olefins using quaternary ammonium heteropolyphosphotungstate catalysts. The system exhibits high conversion and selectivity as well as excellent catalyst stability in the epoxidation of olefins using H2O2 as the oxidant. For example, for cyclohexene epoxidation in an aqueous/oil biphasic system, the conversion based on H2O2 was 92% and the selectivity was 94%. This catalytic process has been commercialized in China. Using in situ H2O2 generated by the oxidation of 2-ethylanthrahydroquinone (EAHQ), the selectivity for propylene oxide (PO) based on propylene was 95%, and the yield based on EAHQ was 85%. The catalytic system is homogeneous during the epoxidation; however, after the H2O2 is used up, the catalyst can be recovered as a precipitate and can be reused. Thus, the advantages of both homogeneous and heterogeneous catalysts are combined in one system through reaction-controlled phase transfer.
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