Download PTT102 Aldehydes and Ketones

Rozaini Abdullah
School of Bioprocess Eng
UniMAP
Week 10
Outline
Carbonyl Condensation
 Micheal Reaction

Aldol
Claisen
1. Carbonyl Condensation

Carbonyl compounds are both the electrophile and
nucleophile in carbonyl condensation reactions
Aldol Condensation



Acetaldehyde reacts in basic solution (NaOEt, NaOH)
with another molecule of acetaldehyde
The b-hydroxy aldehyde product is aldol (aldehyde +
alcohol)
This is a general reaction of aldehydes and ketones
General Condensations
5
Mechanism of Aldol Reactions
Aldol reactions, like
all carbonyl
condensations,
occur by
nucleophilic addition
of the enolate ion of
the donor molecule
to the carbonyl
group of the
acceptor molecule
 The addition
intermediate is
protonated to give
an alcohol product

Predicting Aldol Products
The product will have an alcohol and a carbonyl in a
1,3 relationship (a beta-hydroxy carbonyl)
1. Claisen Condensation
Condensation of Two Ester Molecules.
 The product of a Claisen condensation is a βketo ester.
 In a Claisen condensation, one molecule of
carbonyl compound is the nucleophile and second
molecule is electrophile.
 The new C-C bond connect the α-carbon of one
molecule and the carbon that was formerly the
carbonyl carbon of the other molecule

Mechanism of the Claisen
Condensation

Similar to aldol
condensation:
nucleophilic acyl
substitution of an ester
enolate ion on the
carbonyl group of a
second ester molecule

If the starting ester has more
than one acidic a hydrogen, the
product b-keto ester has a doubly
activated proton that can be
abstracted by base

Requires a full equivalent of base
rather than a catalytic amount

The deprotonation drives the
reaction to the product
Learning Check:
Predict the product of Claisen condensation of ethyl propanoate
Solution:
Predict the product of Claisen condensation of ethyl propanoate
Mixed Claisen Condensations

Successful when one of the two esters acts as the
electrophilic acceptor in reactions with other ester
anions to give mixed b-keto esters
2.Conjugate Carbonyl Additions: The
Michael Reaction

Enolates can add as nucleophiles to ,b-unsaturated
aldehydes and ketones to give the conjugate
addition product
Mechanism of the Michael

Nucleophilic
addition of a
enolate ion
donor to the b
carbon of an
,bunsaturated
carbonyl
acceptor
Learning Check:

Make the following using a Michael Reaction:
Solution:

Make the following using a Michael Reaction:
Learning Check:
Which of the following statements explains why the following aldehyde
will not undergo an aldol reaction with itself?
1.
2.
3.
4.
5.
The benzene ring makes the carbonyl group unreactive towards
aldol reactions.
A carbonyl group must be connected to two alkyl groups in order
to undergo an aldol reaction.
The molecule does not possess any hydrogens α to the carbonyl
group.
Electrophilic aromatic substitution competes favorably with the
aldol reaction.
Nucleophilic acyl substitution competes favorably with the aldol
reaction.
Solution:
Which of the following statements explains why the following aldehyde
will not undergo an aldol reaction with itself?
1.
2.
3.
4.
5.
The benzene ring makes the carbonyl group unreactive towards
aldol reactions.
A carbonyl group must be connected to two alkyl groups in order
to undergo an aldol reaction.
The molecule does not possess any hydrogens α to the carbonyl
group.
Electrophilic aromatic substitution competes favorably with the
aldol reaction.
Nucleophilic acyl substitution competes favorably with the aldol
reaction.
Learning Check:
Predict the aldol reaction product of the following ketone.
O
NaOH
Ethanol
1.
2.
O
3.
O
OH
O
OH
HO
4.
5.
O
OH
O
OH
Solution:
Predict the aldol reaction product of the following ketone.
O
NaOH
Ethanol
1.
2.
O
3.
O
OH
O
OH
HO
4.
5.
O
OH
O
OH
Learning Check:
What type of reaction occurs in a Claisen condensation?
1.
2.
3.
4.
5.
electrophilic
aromatic substitution
nucleophilic addition
hydrolysis
nucleophilic acyl
substitution
decarboxylation
Solution:
What type of reaction occurs in a Claisen condensation?
1.
2.
3.
4.
5.
electrophilic
aromatic substitution
nucleophilic addition
hydrolysis
nucleophilic acyl
substitution
decarboxylation
Learning Check:
Select the correct Claisen condensation product for the
following reaction.
1.
3.
2.
4.
5.
Solution:
Predict the outcome of the following reaction.
1.
2.
4.
3.
5.