Print
ESTERS THEORY
Hits: 59263

When an ester with hydrogens a is treated with an equivalent of base (alkoxide) it condenses to form a product of the family of 3-ketoesters. This type of reaction is known as a Claisen condensation.

 
condensacion-claisen
 
Ethyl ethanoate [1] condenses in the presence of an equivalent of ethoxide in ethanol followed by an acid stage, to form ethyl 3-oxobutanoate [2] (3-ketoester)
 
The mechanism of the Claisen condensation proceeds in a similar way to that of the aldol condensation. In a first stage an ester enolate is formed which condenses on the carbonyl of another ester molecule. The equilibria are unfavorable and it requires a last acid-base stage to displace them.
 
Step 1. Formation of the ester enolate
 
condensacion-claisen
 
Step 2. Nucleophilic addition
 
condensacion-claisen
 
Stage 3. Ethoxide removal
 
condensacion-claisen
 
Stage 4. Transformation of the 3-ketoester into its enolate. This stage is the first favorable equilibrium of the Claisen and it displaces all previous equilibria towards the final product.
 
condensacion-claisen
 
Step 5. Protonation of the keto-ester enolate
 
condensacion-claisen