Epoxide

An epoxide is a cyclic ether with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale for many applications. In general, low molecular weight epoxides are colourless and nonpolar, and often volatile.Bisphenol A diglycidyl ether is a component in common household 'epoxy'.The chemical structure of the epoxide glycidol, a common chemical intermediate.Epothilones are naturally occurring epoxides.3,4-Epoxycyclohexylmethyl-3’,4’-epoxycyclohexane carboxylate, precursor to coatings.Epoxidized linolein, a major component of epoxidized soybean oil (ESBO), a commercially important plasticizer.Benzene oxide exists in equilibrium with the oxepin isomer. An epoxide is a cyclic ether with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale for many applications. In general, low molecular weight epoxides are colourless and nonpolar, and often volatile. A compound containing the epoxide functional group can be called an epoxy, epoxide, oxirane, and ethoxyline. Simple epoxides are often referred to as oxides. Thus, the epoxide of ethylene (C2H4) is ethylene oxide (C2H4O). Many compounds have trivial names; for instance, ethylene oxide is called 'oxirane'. Some names emphasize the presence of the epoxide functional group, as in the compound 1,2-epoxyheptane, which can also be called 1,2-heptene oxide. A polymer formed from epoxide precursors is called an epoxy, but such materials do not contain epoxide groups (or contain only a few residual epoxy groups that remain unreacted in the formation of the resin). The dominant epoxides industrially are ethylene oxide and propylene oxide, which are produced respectively on the scales of approximately 15 and 3 million tonnes/year. The epoxidation of ethylene involves its reaction of oxygen according to the following stoichiometry: The direct reaction of oxygen with alkenes is useful only for this epoxide. Modified heterogeneous silver catalysts are typically employed. Other alkenes fail to react usefully, even propylene, though TS-1 supported Au catalysts can perform propylene epoxidation selectively. Aside from ethylene oxide, most epoxides are generated by treating alkenes with peroxide-containing reagents, which donate a single oxygen atom. Safety considerations weigh on these reactions because organic peroxides are prone to spontaneous decomposition or even combustion. Metal complexes are useful catalysts for epoxidations involving hydrogen peroxide and alkyl hydroperoxides. Peroxycarboxylic acids, which are more electrophilic, convert alkenes to epoxides without the intervention of metal catalysts. In specialized applications, other peroxide-containing reagents are employed, such as dimethyldioxirane. Depending on the mechanism of the reaction and the geometry of the alkene starting material, cis and/or trans epoxide diastereomers may be formed. In addition, if there are other stereocenters present in the starting material, they can influence the stereochemistry of the epoxidation. Metal-catalyzed epoxidations were first explored using tert-butyl hydroperoxide (TBHP). Association of TBHP with the metal (M) generates the active metal peroxy complex containing the MOOR group, which then transfers an O center to the alkene. Organic peroxides are used for the production of propylene oxide from propylene. Catalysts are required as well. Both t-butyl hydroperoxide and ethylbenzene hydroperoxide can be used as oxygen sources.