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Chemistry LibreTexts

Claisen Condensation

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Claisen condensation, not to be confused with Claisen rearrangement, is the reaction of an enolizable ester with a strong base to give a β-ketoester.

claisencondensation1.png

The most commonly used strong base in organic reactions, hydroxide ion, is not suitable for Claisen condensation because it could cause saponification of the ester. The base of choice in Claisen condensation is the alkoxide ion corresponding to the alkoxy group in the ester. Other alkoxides could cause transesterification of the ester. Since the β-ketoester formed in Claisen condensation is converted to the corresponding enolate ion by the base, in order to isolate the β-ketoester, when the reaction is complete, the reaction mixture needs to be acidified.

eg:

claisencondensation2.png

Mechanism

Step 1: The alkoxide ion deprotonates the enolizable ester reversibly.


claisencondensation3.png

Step 2 and 3: Enolate ion 1 undergoes a nucleophilic acyl substitution with the unreacted ester to give the β-ketoester.

claisencondensation4.png

Step 4: The alkoxide ion deprotonates the β-ketoester irreversibly.

claisencondensation5.png

Step 5: The acid protonates enolate ion 2.

claisencondensation6.png

see also Dieckmann condensation


This page titled Claisen Condensation is shared under a All Rights Reserved (used with permission) license and was authored, remixed, and/or curated by Gamini Gunawardena via source content that was edited to the style and standards of the LibreTexts platform.

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