Claisen condensation between

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Mechanism of the
Claisen condensation between
Ethyl Benzoate and Ethyl Propanoate
Rainer Ludwig Claisen (1851-1930) Developed the
Claisen Condensation in 1887
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What are the building blocks?
ETHYL PROPANOATE
ETHYL BENZOATE
CARBON
ETHOXIDE ION
HYDROGEN
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sp2 orbitals
O
O
p orbitalsp bond
a hydrogens
C
C
C
O
C
sp3 orbitals
C
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High Electronegativity of Oxygen
FORCE ENERGY
Sites for nucleophilic attacks
O
C
C
a hydrogens
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FORCE ENERGY
Resonance EnergyStabilization energy
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FORCE ENERGY
O
Formation of the enolate
-
Et -O - C - CH CH3
Condensationwith ethyl benzoate to form ß-keto
ester
Loss of 2nd alpha hydrogen on ß-keto ester
Ethyl propanoate
O
Et -O - C - CH2 CH3
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MATHEMATICS
pKa of alpha hydrogens 24 or Ka 10-24
0.06
0.06
0.14
0.04
Ethyl Propanoate
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MATHEMATICS
Bond Angles
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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.
Ethyl Propanoate
5. A ß-keto ester is formed.
Ethoxide ion
Ethyl Benzoate
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Deprotonation of Ethyl Propanoate
The enolate ion is a strong nucleophile and will
attack the partially positive carbon of a
carbonyl group.
Resonance
Ethyl Benzoate
Enolate of
Ethyl Propanoate
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Self condensation of ethyl propanoate
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Mechanism of the
Claisen condensation between
Ethyl Benzoate and Ethyl Propanoate
Rainer Ludwig Claisen (1851-1930) Developed the
Claisen Condensation in 1887