Alkene hydration (Markovnikov)
Abstract
Alkene hydration is a reaction that converts an alkene into an alcohol by addition of water across the alkene double bond. The transformation is most commonly performed under acidic conditions using a strong acid catalyst and proceeds with Markovnikov regioselectivity.
Keywords
Alkene, Alcohol, Markovnikov
Category
Alkene
Mechanism
Mechanistically, the reaction starts with protonation of the alkene, generating the most stable, i.e. the most substituted, carbocation intermediate. The carbocation then undergoes a nucleophilic addition of a molecule of water, forming an oxonium ion. Finally, deprotonation by another water molecule regenerates the acid catalyst and yields the corresponding alcohol. Overall, the hydroxyl group is installed on the more substituted carbon atom and the hydrogen atom on the less substituted carbon, following Markovnikov’s rule.
It is important to note that, because the reaction proceeds through a carbocation intermediate, rearrangements such as hydride or alkyl shifts may occur if a more stable carbocation can be formed. Alkene oxymercuration provides a valuable alternative, as it achieves Markovnikov hydration without the formation of a free carbocation and therefore avoids such rearrangements.
