Oxymercurationdemercuration

Oxymercuration-demercuration is a two-step method for converting alkenes into alcohols with Markovnikov regioselectivity while avoiding carbocation rearrangements. In the first step, mercuric acetate (Hg(OAc)2) is added to the alkene in the presence of water (often with a co-solvent such as THF) to form a bridged mercurinium ion. Water then opens the ion, delivering an organomercury intermediate that bears a hydroxyl group on the more substituted carbon. In the second step, the mercury is removed by reduction, typically with sodium borohydride (NaBH4), yielding the corresponding alcohol and leaving mercury as a reduced byproduct.

Mechanistically, the reaction proceeds through an electrophilic addition that proceeds without forming a free carbocation, thereby avoiding rearrangements common to acid-catalyzed hydration. The process is generally described as anti addition: the hydroxyl group and the mercury-containing substituent add to opposite faces of the original double bond, and subsequent demercuration replaces the mercury fragment with hydrogen, preserving the newly installed OH group.

The method is widely used because it provides Markovnikov hydration of alkenes without rearrangements and is compatible with a broad range of functional groups. It can be performed on many terminal and internal alkenes, though the reaction uses toxic mercury reagents and generates mercury waste, raising safety and environmental concerns. Stereochemical outcomes depend on the substrate and reaction conditions, but the overall transformation delivers anti addition across the double bond, followed by demercuration to give the alcohol.