monoepoxide

A monoepoxide is an organic compound that contains a single epoxide group, i.e., one oxirane ring, within its molecular framework. The term distinguishes such molecules from diepoxides (two epoxide rings) and polyepoxides (three or more). The epoxide ring is the defining feature of a monoepoxide and is typically the site of chemical reactivity.

The epoxide ring is a three-membered cyclic ether that is highly strained, making monoepoxides relatively reactive toward nucleophiles and acids. They can be based on aliphatic, cycloalkyl, or aromatic backbones. Common examples include ethylene oxide (oxirane), propylene oxide, and various aryl or cycloalkyl epoxides such as styrene oxide.

Most monoepoxides are prepared by oxidation of alkenes with a peracid (the Prilezhaev reaction), which converts a single C=C bond into an epoxide. Selective epoxidation can yield monoepoxides in molecules bearing multiple double bonds, and halohydrin cyclization or base-induced displacement can convert suitable precursors into an epoxide ring.

Reactions of monoepoxides typically involve ring opening due to ring strain. In acid-catalyzed conditions, opening tends to occur at the more substituted carbon, while base- or nucleophile-catalyzed opening favors the less substituted carbon. Nucleophiles such as water, alcohols, or halides can attack to give beta-hydroxy or beta-halo alcohols, respectively. Ring-opening reactions are important steps in organic synthesis and in the production of larger molecules, including polyols and various polymers.

Applications of monoepoxides include use as intermediates in organic synthesis and as monomeric units or precursors for polyol- or polyether-based materials. They can be hazardous and are typically handled under controlled conditions due to their reactivity and potential irritant or toxic properties.