The mechanism of the mercury(II)-catalyzed alkyne hydration reaction is analogous to the oxymercuration reaction of alkenes. Electrophilic addition of mercury(II) ion to the alkyne give a vinylic cation, which reacts with water and loses a proton to yield a mercury-containing enol intermediate. In contrast to alkene oxymercuration, no tretment with NaBH4 is necessary to remove the mercury; the acidic reaction conditions alone are sufficient to effect replacement of mercury by hydrogen.