oxymercuration

Oxymercuration, or oxymercuration-demercuration, is a two-step method for the hydration of alkenes that furnishes alcohols with Markovnikov regioselectivity without carbocation rearrangements. The process uses mercuric acetate and water to add a mercury-containing group and a hydroxyl group across the double bond, followed by a reductive removal of mercury to reveal the alcohol.

In the first step, Hg(OAc)2 adds to the alkene to form a mercurinium ion intermediate. Water acts as the nucleophile and attacks the more substituted carbon of the three-membered ion, opening the ring in an anti fashion and giving an organomercury alcohol intermediate. The second step reduces the C–Hg bond, typically with sodium borohydride (NaBH4), to remove mercury and yield the corresponding alcohol while acetate byproducts are formed.

The overall transformation hydrates the alkene to a Markovnikov alcohol without carbocation rearrangements, a key advantage over simple acid-catalyzed hydration. The reaction proceeds under relatively mild conditions and can tolerate a variety of functional groups. The stereochemical outcome involves anti addition in the oxymercuration step, with the final product depending on the substrate’s geometry.

Limitations and considerations include the use of toxic mercury reagents and the need for appropriate waste disposal. While oxymercuration-demercuration is useful for substrates prone to rearrangements with acid-catalyzed hydration, it is often balanced against greener alternatives such as hydroboration-oxidation for anti-Markovnikov hydration or hydraton methods that avoid mercury altogether.