When alkynes are reacted with water, aldehydes and ketones are formed. While internal alkynes can only be converted to ketones by acid-catalyzed hydration or oxymercuration-demercuration, terminal alkynes can also be converted to aldehydes via anti-Markovnikov addition of hydroboration-oxidation:
So, contrary to what it may look like, alkynes cannot be converted to alcohols by hydration reactions because the alcohol (enol) that is formed after the addition to one of the π bonds is unstable and tautomerizes (KET) to the corresponding aldehyde or the ketone:
Alkynes to Alcohols Via Hydration of Alkenes
One way of converting alkynes to alcohols would be reducing them first to alkenes and then hydrating the alkene by a Markovnikov or anti-Markovnikov addition of water:
Don’t forget to watch for rearrangements in acid-catalyzed hydration or any other addition reaction via carbocation intermediates. Oxymercuration-demercuration can be used to avoid rearrangements in acid-catalyzed hydrations of alkenes.
Alkynes to Alcohols Via Reduction of Carbonyls
If you are already familiar with the reduction reactions of carbonyl compounds such as aldehydes and ketones, you can also hydrate the alkyne followed by a reduction to the target alcohol:
Aldehydes and ketones are relatively easy to reduce and this can be done by catalytic hydrogenation, using NaBH4, and LiAlH4:
Another indirect way of converting alkynes to alcohols is their ozonolysis or the reaction with KMnO4. The product here is a carboxylic acid, which generally requires a strong reducing agent such as LiAlH4:
To summarize, when asked to convert alkynes to alcohols, think of an alkyne-aldehyde/ketone or carboxylic acid – alcohol.
Organic Chemistry Reaction Maps
Never struggle again to figure out how to convert an alkyl halide to an alcohol, an alkene to an alkyne, a nitrile to a ketone, a ketone to an aldehyde, and more! The comprehensive powerfull Reaction Maps of organic functional group transformations are here!
Check Also
- Introduction to Alkynes
- Naming Alkynes by IUPAC Nomenclature Rules – Practice Problems
- Preparation of Alkynes by Elimination Reactions
- Hydrohalogenation of Alkynes
- Addition of Water to Alkynes
- Acid-Catalyzed Hydration of Alkynes with Practice Problems
- Reduction of Alkynes
- Halogenation of Alkynes
- Hydroboration-Oxidation of Alkynes with Practice Problems
- Ozonolysis of Alkynes with Practice Problems
- Alkylation of Terminal Alkynes in Organic Synthesis with Practice Problems
- Reactions of Acetylide Ions
- Alkyne reactions summary practice problems
- Alkyne Synthesis Reactions Practice Problems
- Alkyne Naming and Reactions Practice Quiz
- Reactions Map of Alkynes