Keto-enol interconversion is also called keto-enol tautomerization or enolization. The interconversion of the tautomers can be catalysed by either acids or bases. In a basic solution, hydroxide ion removes a proton from the a-carbon of the keto tautomer, forming an enolate ion. Protonation on oxygen forms the enol tautomer, whereas protonation on the a-carbon re-forms the keto tautomer.
Base-catalyzed keto-enol interconversion.

In an acidic solution, the carbonyl oxygen of the keto tautomer is protonated and water removes a proton from the a-carbon, forming the enol.
Acid-catalyzed keto-enol interconversion.