Which reagent combination would you use to hydrate a terminal alkyne to a methyl ketone?

Which reagent combination would you use to hydrate a terminal alkyne to a methyl ketone?

• A. H2SO4/HgSO4 (or HgSO4)
• B. O3 followed by DMS
• C. H2O2 and AcOH
• D. Baeyer-Villiger oxidation

Answer: (A)

Hydration of terminal alkynes under acidic, mercury-catalyzed conditions adds water across the triple bond in a Markovnikov fashion and then tautomerizes to the corresponding methyl ketone. For a terminal alkyne of the form R-C≡CH, this sequence gives the product R-CO-CH3, with the carbonyl on the internal carbon. That specific pathway is unique to this HgSO4/H2SO4–water system, which is why it reliably yields a methyl ketone from terminal alkynes. Other options pose different transformations. Ozonolysis would cleave the triple bond into carbonyl fragments rather than producing a single methyl ketone. The peroxide/acid system and other oxidations don’t implement the hydration-to-ketone pathway, and Baeyer-Villiger oxidation targets ketones to esters rather than forming the methyl ketone from an alkyne.

Hydration of terminal alkynes under acidic, mercury-catalyzed conditions adds water across the triple bond in a Markovnikov fashion and then tautomerizes to the corresponding methyl ketone. For a terminal alkyne of the form R-C≡CH, this sequence gives the product R-CO-CH3, with the carbonyl on the internal carbon. That specific pathway is unique to this HgSO4/H2SO4–water system, which is why it reliably yields a methyl ketone from terminal alkynes.

Other options pose different transformations. Ozonolysis would cleave the triple bond into carbonyl fragments rather than producing a single methyl ketone. The peroxide/acid system and other oxidations don’t implement the hydration-to-ketone pathway, and Baeyer-Villiger oxidation targets ketones to esters rather than forming the methyl ketone from an alkyne.