Alkenes: Epoxide Reactions

Alkenes are capable of reacting with oxygen in the presence of elemental silver to form a series of cyclic ethers called epoxides. Epoxides are three‐atom cyclic systems in which one of the atoms is oxygen. The simplest epoxide is epoxyethane (ethylene oxide).

Epoxyethane belongs to a class of chemicals called heterocyclic compounds. These compounds are cyclic structures in which one (or more) of the ring atoms is a hetero atom, that is, an atom of an element other than carbon. In the laboratory, epoxyethane is prepared by reacting 1‐chloro‐2‐hydroxyethane with a base.

The mechanism for this reaction starts with the base reacting with the acidic hydrogen of the OH group.

The oxygen anion is then attracted to the carbon that is bonded to the chlorine atom. This carbon bears a strong partial positive charge due to the great differences in electronegativity between the carbon and chlorine atoms.

As can be seen in the structural formula above, the oxygen atom must be located anti to the departing chlorine atom for the reaction to occur. The overall reaction is a syn addition.

A third method of preparing epoxyethane is by the reaction of an alkene with peroxy acids.