Transcript Claisen Condensation PowerPoint (2 Megs)

Rainer Ludwig Claisen (1851-1930)
Developed the “Claisen
Condensation” in 1887
What are the building blocks?
sp2 orbitals
p orbitals
π bond
α hydrogens
sp3 orbitals
High Electronegativity
of Oxygen
Sites for
nucleophilic
attacks
α hydrogens
Resonance Energy
“Stabilization energy”
Formation of
the enolate
O
||
-
Et -O - C - CH – CH3
Ethyl propanoate
O
||
Et -O - C - CH2 – CH3
Condensation
with ethyl
benzoate to form
β-keto ester
Loss of 2nd alpha
hydrogen on βketo ester
pKa of alpha hydrogens ≈ 24 or Ka ≈ 10-24
0.04
Ethyl Propanoate
Bond Angles
sp3 orbitals
sp2 orbitals
120o
109.5o
180o
90o
sp orbitals
p orbitals
Overview of the Claisen Condensation Reaction
Ethyl Propanoate
Ethyl Benzoate
+
3.
The enolate
of ethyl
2. The
enolate
ofion
ethyl
1.
Ethoxide
acting
6. The driving force for this as
propanoate
issubstitution
a strong
4.
The
alpha
propanoate
isbase
a
strong
reaction is the transfer of the
nucleophile
attacks
makes thisthat
aethyl
carbonyl
formed.
deprotonates
second alpha hydrogen to
the
partially positive
condensation
propanoate.
the ethoxide ion. This is
carbon
of the carbonyl
reaction.
exothermic.
5. A β-keto
ester
is
group
on ethyl
benzoate.
Ethoxide ion
formed.
Deprotonation of Ethyl Propanoate
TheResonance
enolate ion is a strong nucleophile
and will attack the partially positive
carbon of a carbonyl group.
Ethyl Benzoate
+
Enolate of
Ethyl Propanoate
Self condensation of ethyl propanoate
Rainer Ludwig Claisen (1851-1930)
Developed the “Claisen
Condensation” in 1887