Epoxides

Epoxides, or oxiranes, are a class of organic compounds featuring a highly strained three-membered ring containing one oxygen atom. The oxirane ring is more reactive than ordinary ethers, making epoxides prone to ring opening by nucleophiles or acids. They are commonly prepared by oxidation of alkenes.

The most widespread preparation involves epoxidation of alkenes with oxidants such as meta-chloroperoxybenzoic acid (mCPBA) or hydrogen peroxide, often in the presence of a catalyst. Other routes include oxidation with dimethyl dioxirane or catalytic systems designed for enantioselective epoxidation. In asymmetric synthesis, chiral catalysts enable enantioselective epoxidations, such as Sharpless-type methods for allylic alcohols and various metal-salen catalysts for diverse substrates.

Epoxidation is generally stereospecific, adding oxygen across the double bond in a syn fashion, so the relative configuration of substituents is preserved in the oxirane product. Epoxides readily undergo ring-opening reactions. Under acidic conditions, nucleophiles attack the more substituted carbon, whereas under basic or neutral conditions, attack tends to occur at the less hindered carbon, yielding beta-hydroxy or diol products after workup.

Applications of epoxides are broad. They are central to epoxy resins and curing systems used in coatings and composites. Glycidyl ethers and other epoxide-derived intermediates are important in polymer chemistry. Small epoxides such as ethylene oxide and propylene oxide serve as versatile chemical intermediates. Some epoxides are toxic or carcinogenic and require careful handling.