Definition

Halohydrins treated with strong base (such as hydroxide anion) can form epoxides through with intramolecular SN2 reaction.

Structural reaction scheme for Epoxide formation [from halohydrins], diagram 1 of 3
Figure 1. Epoxide formation [from halohydrins]

Explanation

When alkenes treated with a halogen in the presence of water they will be converted into halohydrins which can be converted further into epoxides.

Structural reaction scheme for Epoxide formation [from halohydrins], diagram 2 of 3
Figure 2. Epoxide formation [from halohydrins]


Mechanism of epoxide formation

Structural reaction scheme for Epoxide formation [from halohydrins], diagram 3 of 3
Figure 3. Epoxide formation [from halohydrins]

This process achieved via an Williamson ether synthesis. Hydroxide deprotonates the halohydrin and an alkoxide ion is formed. Then this ion acts as a nucleophile in an intramolecular SN2 mechanism ejecting the bromide as a leaving group.