Alkynes can be converted into carboxylic acids by ozonolysis. For external alkynes, the ozonolysis results in a carboxylic acid and carbon dioxide:
The ozonolysis of internal alkynes, on the other hand, produces two carboxylic acids:
In the reaction above, the alkyne is symmetrical, as there are two identical R groups on both sides of the triple bond. As a result, two molecules of the same carboxylic acid are formed from one molecule of the alkyne.
If the alkyne is unsymmetrical, then two different carboxylic will be formed:
Alkynes to Carboxylic Acids Using KMnO4
Another direct way of converting alkynes to carboxylic acid is the reaction with potassium permanganate (KMnO4) under basic conditions followed by acidic workup. This, like the ozonolysis, is an oxidative cleavage of the alkynes:
And, just like in the ozonolysis of internal alkynes, two carboxylic acids are produced:
It is worth mentioning that under milder conditions when no base or acid is used, vicinal dicarbonyls are obtained:
Indirect Conversion of Alkynes to Carboxylic Acids
We know, from the hydroboration-oxidation of alkynes, that an aldehyde can be obtained via anti-Markovnikov addition to the triple bond:
We can oxidize the aldehyde to carboxylic acid using any of the strong oxidizing agents such as H2CrO4, KMnO4, and NaClO mentioned in the article on oxidation of alcohols:
Notice that all the other hydration reactions of alkynes proceed via Markovnikov addition, and therefore, only ketones can be obtained. Recall that ketones cannot be oxidized further to carboxylic acids.
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