Summary of Epoxide Chemistry

Epoxides, summary of chemistry, 290 Equatorial bond, 168 Equilibrium and free energy, 36 Equivalent H s, 50 Erythro form, 82, 85 Esters, formation, 338 inorganic, 262, 272, 276 reduction, 261 Ethers, cleavage, 282 crown, 286 cyclic, 285 silyl, 286... 

In summary, epoxides are produced not only as endproducts, but also as intermediates because they are valuable building blocks in synthetic organic chemistry [82-84] (Table 1.3). Until recently, epoxide intermediates were produced by direct oxygen transfer to olefins by a variety of stoichiometric methods. Recently, considerable efforts have been made to conduct the transformations selectively under catalytic conditions. Because epoxides are reactive substances, they can undergo diverse transformations by reactions with acids and bases, and their reactivity has been exploited to form a diverse range of products by so-called click chemistry [85,86], which combines the breadth of combinatorial methods with the precise synthesis of organic chemistry. 

In summary, the TS-1 catalyzed epoxidation of propylene with H2O2 to PO is a thoroughly investigated epoxidation reaction. The oxidation chemistry is well known by now, and the catalyst, and the process parameters have been optimized. Currendy, the titanium-based catalyst is in the process of being commerciahzed. Computational chemistry has been appHed to elucidate the details of the surface chemistry and to identify the important reaction steps at this point, various competing mechanisms, proposed by different authors, can be found in the literature. 

The in situ procedure as proposed by Sonnet et al. (18) is much more attractive for synthetic applications. With the use of only a moderate excess of monopersulfate (C=C KHSO5 = l 2-2.4), they achieved an 80% yield for the epoxidation of oleic acid methyl ester and 81-96% for the epoxidation of various plant oils. It is a twophase reaction with a crown-ether as phase-transfer catalyst yet a considerable amount of inorganic waste (six times the weight of the product) is produced. In a recent work (21), the phase-transfer catalyst was replaced by acetonitrile as a polar solvent. In summary, epoxidation by dioxiranes is a promising new method for oleo-chemistry, especially because it also works in combination with metal catalysts to influence diastereoselectivity (22) an enantioselective epoxidation with sugardioxiranes has also been reported (23). 

Epoxides may also be formed by oxidation of alkenes with other reagents. For a summary, see Hudlicky, M. Oxidations in Organic Chemistry, ACS Monograph No. 186 American Chemical Society Washington, DC, 1990. Dehydrohalogenation of halohydrins is another path to epoxides. 

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