An epoxide is a cyclic ether with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained and they are produced on a large scale for many applications. In general, low molecular weight epoxides are colourless and nonpolar, 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 is ethylene oxide. Many compounds have trivial names, ethylene oxide is called oxirane, some names emphasize the presence of the epoxide functional group, as in the compound 1, 2-epoxycycloheptane, which can also be called 1, 2-heptene oxide. A polymer formed from epoxide precursors is called an epoxy, 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. Other alkenes fail to react usefully, even propylene, many epoxides are generated by treating alkenes with peroxide-containing reagents, which donate a single oxygen atom. Outside of the scale, the main challenge with this approach is that typical peroxides are more valuable than the product epoxides. For this reason, this methodology is restricted to fine chemical applications, metal complexes are useful catalysts for these reactions. Typical peroxide reagents include hydrogen peroxide, peroxycarboxylic acids, and alkyl hydroperoxides, in specialized applications, other peroxide-containing reagents are employed, such as dimethyldioxirane. Depending on the mechanism of the reaction and the geometry of the starting material. In addition, if there are other stereocenters present in the starting material, the metal-catalyzed epoxidation was first explored using tert-butyl hydroperoxide as a source of an O atom. Association of TBHP with the metal generates the active metal catalyst with a peroxy ligand and this approach is used for the production of propylene oxide from propylene using various catalysts. Both t-butyl hydroperoxide or ethylbenzene hydroperoxide can be used as oxygen sources, more typically for laboratory operations, the Prilezhaev reaction is employed. This approach involves the oxidation of the alkene with a such as m-CPBA. Illustrative is the epoxidation of styrene with perbenzoic acid to styrene oxide, the peroxide is viewed as an electrophile, and the alkene a nucleophile. The reaction is considered to be concerted. The butterfly mechanism allows ideal positioning of the O-O sigma star orbital for C-C Pi electrons to attack, hydroperoxides are also employed in catalytic enantioselective epoxidations, such as the Sharpless epoxidation and the Jacobsen epoxidation. Together with the Shi epoxidation, these reactions are useful for the synthesis of chiral epoxides
A generic epoxide.
Image: Methyloxirane from 2 chloropropionic acid
Simplified mechanism for metal-catalyzed epoxidation of alkenes with peroxide (ROOH) reagents.