Is the hydration of phenylacetylene an antimarkovnikov behaviour?

1 Answer
Jan 11, 2015

No, the hydration of phenylacetylene corresponds to the Markovnikov addition of water across the C≡C bond.

The hydration is catalyzed by gold(I) and gold(III) complexes and by mercury(II) ions.

The mechanism is complex, but the overall result is as if the water adds in a Markovnikov addition across the C≡C bond.

PhC≡CH + H⁺ → PhC⁺=CH₂ → PhC(OH)=CH₂ ⇌ PhC(=O)CH₃

In a Markovnikov addition, the H⁺ adds to the C atom with more hydrogen atoms (the terminal alkyne carbon) to form the vinyl cation.

The OH then attaches to the cationic carbon to form an enol.

The enol tautomerizes to the more stable ketone — acetophenone.