Lewis Acid Catalyzed Epoxidation of Olefins Using Hydrogen Peroxide: Growing Prominence and Expanding Range

Publisher Summary Among the many methods for synthesizing epoxides, Lewis acid catalyzed olefin epoxidation provides a special combination of capabilities including gentle and green processing and selectivity of multiple kinds. The subject has contributed both to the understanding of important basic science and a large and growing inventory of impressive oxidation reactions. Some big challenges have been met by Lewis acid catalysts, but it has yet to provide the underlying science in a major industrial process. Historically, the cost of hydrogen peroxide has been a limitation, but recent developments, especially the on-site and/or in situ generation of H 2 O 2 has been demonstrated for promising alternative processes, especially in the light olefin epoxidation industry. For commodity chemicals, costs and environmental issues are accompanied by other related challenges such as catalyst durability and productivity that thwart otherwise elegant processes. The case of the long known and arguably unique catalyst methyltrioxorhenium for light olefin oxidation is explored in this context. Attention is also directed to the growing realization that, in combination with the right ligands, late transition metal elements, including manganese and iron also catalyze olefin epoxidation reactions. Ordinarily manganese and iron perform epoxidations by the oxygen rebound mechanism of Groves, and engage in one-electron redox chemistry. To produce only epoxides in reacting with many common olefins, the activated catalyst must not abstract hydrogen atoms that would open radical routes to other products. Ligand design has produced highly selective Mn(IV) catalysts capable of converting many olefins into their oxides but limited in their ability to initiate radical processes by hydrogen abstraction.