Tungsten complexes olefin epoxidation

Mimoun and coworkersdescribed the first well-defined example of a d° metal aUtylperoxidic species 49 which epoxidized simple olefins with high selectivity. Several features of the epoxidation performed by 49 resemble those of the Halcon catalytic epoxidation process " . Novel tungsten complexes containing 2 -pyridyl alcoholate ligands like 50 have been synthesized and tested as catalysts in the epoxidation of cw-cyclooctene with TBHP in the absence of solvent . The system displayed modest catalytic activity (100% conversion in 60 h) but excellent product selectivity. 

The tert-huty hydroperoxide is then mixed with a catalyst solution to react with propylene. Some TBHP decomposes to TBA during this process step. The catalyst is typically an organometaHic that is soluble in the reaction mixture. The metal can be tungsten, vanadium, or molybdenum. Molybdenum complexes with naphthenates or carboxylates provide the best combination of selectivity and reactivity. Catalyst concentrations of 200—500 ppm in a solution of 55% TBHP and 45% TBA are typically used when water content is less than 0.5 wt %. The homogeneous metal catalyst must be removed from solution for disposal or recycle (137,157). Although heterogeneous catalysts can be employed, elution of some of the metal, particularly molybdenum, from the support surface occurs (158). References 159 and 160 discuss possible mechanisms for the catalytic epoxidation of olefins by hydroperoxides. 

The epoxidation of olefins with H2O2 and tungstate dates back to 1949 [65], and later received attention by Shell s R D function [66]. Work on these systems has been described in recent reviews [67]. Molybdenum, and particularly tungsten, compounds in solution are versatile epoxidation catalysts, forming diperoxo-complexes (Figure 9.7). 

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