Epoxides, such as propylene oxide, are very important intermediates for the industrial synthesis of various polymers and fine chemicals. Until now, heterogeneous catalysts like the titania-doped zeolite TS-1 are used in large-scale production. Nevertheless, these catalysts often deal with problems of selectivity and decomposition of the oxidation agent. For an efficient synthesis of propylene oxide, high selectivities by using a minimum amount of the oxidant is desired. Therefore, molecular catalysts can be an interesting alternative to the common heterogeneous catalysts. Although a wide spectrum of homogeneous epoxidation catalysts is known, there are only a few reports for the epoxidation of propylene. The biggest disadvantage of homogeneous catalysts is the rather poor recyclability that hinders them to be used for industrial application. Herein, we report the epoxidation of propylene under mild conditions in homogeneous phase using different molecular catalysts and hydrogen peroxide and tert-butyl hydroperoxide as oxidants. A comparison between molybdenum and rhenium catalysts shows high selectivity towards the epoxide for both. Among all investigated catalysts, the well-known rhenium catalyst methyltrioxorhenium outperforms leading to high conversions and selectivities at room temperature under low propylene pressure in acetonitrile solution. Additionally, ionic Lewis basic additives were introduced which exhibit an influence on the stability of the catalyst during catalysis and therefore improve the selectivities. This system offers the opportunity to recycle the catalyst and is one of the unique examples for recycling methyltrioxorhenium.

Molecular catalysts for the efficient epoxidation of propylene

248th National Meeting (2014)

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