Page 126 - Pharm.Org.Chem-I 02-06-05-101

3.C. Addition of water (direct hydration)

• Hydration of an alkyne yields an intermediate enol.
• Enols rapidly isomerizes to aldehydes or ketones (keto–
enol tautomerism).
• Hydration follows Markovnikov’s rule

Terminal alkynes yield methyl substituted ketones.

RH

R C C H + H2O dil. H2SO4 CC
HgSO4 / 60 °C OH

H
enol
catalyst
Vinyl alcohol derivative

2. Hydrogenation

2. A. Catalytic hydrogenation of alkynes to alkanes
Normal hydrogenation over a platinum or palladium
catalyst results in complete saturation to form
alkanes.

2. B. Reduction of Alkynes to cis Alkenes

Hydrogenation using Lindlar’s catalyst (Pd/CaCO3) results
in syn addition of only one equivalent of hydrogen to form
cis alkene. (stereospecific syn addition)

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