Mechanism of the. Claisen condensation between. Ethyl Benzoate and Ethyl Propanoate. Rainer Ludwig Claisen (1851-1930) Developed the “Claisen Condensation” in 1887. What are the building blocks?. ETHYL PROPANOATE. ETHYL BENZOATE . CARBON. ETHOXIDE ION. HYDROGEN. sp 2 orbitals. O.
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p orbitalsπ bond
Sites for nucleophilic attacks
Resonance Energy“Stabilization energy”
Formation of the enolate
Et -O - C - CH – CH3
Condensationwith ethyl benzoate to form β-keto ester
Loss of 2nd alpha hydrogen on β-keto ester
Et -O - C - CH2 – CH3
pKa of alpha hydrogens ≈ 24 or Ka≈ 10-24
Overview of the Claisen Condensation Reaction
3. The enolate of ethyl propanoate is a strong nucleophile that attacks the partially positive carbon of the carbonyl group on ethyl benzoate.
2. The enolate of ethyl propanoate is formed.
1. Ethoxide ion acting as a strong base deprotonates ethyl propanoate.
6. The driving force for this reaction is the transfer of the second alpha hydrogen to the ethoxide ion. This is exothermic.
4. The alpha substitution makes this a carbonyl condensation reaction.
5. A β-keto ester is formed.
Deprotonation of Ethyl Propanoate
The enolate ion is a strong nucleophile and will attack the partially positive carbon of a carbonyl group.