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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. What are the building blocks?. ETHYL PROPANOATE. ETHYL BENZOATE . CARBON. ETHOXIDE ION. HYDROGEN. sp 2 orbitals. O.

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Presentation Transcript
slide1

Mechanism of the

Claisen condensation between

Ethyl Benzoate and Ethyl Propanoate

Rainer Ludwig Claisen (1851-1930)

Developed the “Claisen Condensation” in 1887

slide3

What are the building blocks?

ETHYL PROPANOATE

ETHYL BENZOATE

CARBON

ETHOXIDE ION

HYDROGEN

slide4

sp2 orbitals

O

O

p orbitalsπ bond

α hydrogens

C

C

C

O

C

sp3 orbitals

C

slide5

High Electronegativity of Oxygen

FORCE &

ENERGY

Sites for nucleophilic attacks

O

C

C

α hydrogens

slide6

FORCE &

ENERGY

Resonance Energy“Stabilization energy”

slide7

FORCE &

ENERGY

O||

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

Ethyl propanoate

O||

Et -O - C - CH2 – CH3

slide8

MATHEMATICS

pKa of alpha hydrogens ≈ 24 or Ka≈ 10-24

0.06

0.06

0.14

0.04

Ethyl Propanoate

slide9

sp3 orbitals

sp2 orbitals

109.5o

120o

90o

180o

p orbitals

sp orbitals

MATHEMATICS

Bond Angles

slide10

+

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 β-keto ester is formed.

Ethoxide ion

Ethyl Benzoate

slide11

+

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

slide15

Mechanism of the

Claisen condensation between

Ethyl Benzoate and Ethyl Propanoate

Rainer Ludwig Claisen (1851-1930)

Developed the “Claisen Condensation” in 1887