Claisen condensation

Reaction Mechanism of Claisen condensation

Esters with α-hydrogen atom on treatment with a strong base, e.g. C₂H₅ONa, undergo self condensation to produce β-keto esters.

CH₃COCH₂COOC₂H₅

An α-hydrogen in an ester is weakly acidic than  the α-hydrogen of aldehydes or ketones, because the carbonyl group helps accommodate the negative charge of the carbanion to a lesser extent.

When ethyl acetate is treated with sodium ethoxide, and the resulting mixture is acidified, ethyl 3-oxobutanoate, generally known as ethyl acetoacetate or acetoacetic ester is obtained.

Mixed Claisen Condensation

A reaction similar to a mixed Claisen condensation is the condensation of the ketone and an ester. Because the α-hydrogens of a ketone are more acidic than those of an ester, primarily one product is formed if the ketone is added slowly to a mixture of the base and excess ester. The product is a β-diketone.

A β-keto aldehyde is formed when a ketone condenses with formate esters.

A β-keto ester is formed when a ketone condenses with diethyl carbonate.

Intramolecular Claisen Condensation

Dieckmann Condensation: The addition of base to a 1,6-diester causes the diester to undergo intramolecular Claisen Condensation, thereby forming a five membered ring β-keto ester. An intramoelcular Claisen Condensation is called a Dieckmann Condensation.

Example of Claisen condensation

List of Name Reaction of Organic Chemistry consist of detail Reaction Mechanism of all name reactions of Organic Chemistry.