epoxide

An epoxide, also called oxirane, is a highly reactive cyclic ether consisting of a three-membered ring with two carbon atoms and one oxygen atom. The ring strain of this compact ring drives many of its chemical reactions, making epoxides susceptible to nucleophilic ring-opening and other transformations.

Most simple epoxides are derived from alkenes by the addition of an oxygen atom across the carbon–carbon double bond. The parent compound is oxirane; common substituted epoxides are named as alkene-derived oxiranes, such as ethylene oxide or propylene oxide. Epoxides are typically liquids or low-melting solids, with properties influenced by substituents on the ring.

Synthesis may proceed by oxidation of alkenes using peracids (for example, m-chloroperbenzoic acid) or catalytic systems. Asymmetric epoxidation methods, including Sharpless epoxidation and Jacobsen–Katsuki epoxidation, allow enantioselective formation of epoxides from suitably substituted alkenes.

Reactions of epoxides center on opening of the three-membered ring. Under acidic conditions, protonation of the epoxide oxygen promotes opening by nucleophiles at the more substituted carbon. Under basic or neutral conditions, nucleophiles tend to attack the less substituted carbon in an SN2-like fashion. Ring-opening products can yield beta-hydroxy compounds after workup, and can be steered toward different regiochemical outcomes by the reaction conditions and nucleophile used.

Applications are widespread. Epoxides are key intermediates in organic synthesis and are used to make polyethers and other polymers; epoxy resins are formed by polymerizing epoxides with curing agents. Ethylene oxide is a major industrial chemical used to produce ethylene glycols, solvents, and sterilants. Safety considerations include its reactivity and potential toxicity; handling requires appropriate controls and ventilation.