The aldol condensation is a reaction where carbonyl compounds undergo condensation in the presence of a base to form β-hydroxy aldehydes or ketones. It can occur between two aldehydes, two ketones, or a mixed aldehyde and ketone. The reaction involves the base-catalyzed formation of an enolate ion from the α-hydrogen of one carbonyl compound, which then undergoes nucleophilic addition to the carbonyl carbon of the second reactant. Removal of a water molecule produces the β-hydroxy aldehyde or ketone product.

1. ALDOL condensation
A property of carobnyl
compounds having α-hydrogen

2. ALDOL condensation
• Aldol means aldehyde and alcohol groups on the same
molecule
• May occur between two aldehydes (aldols) or ketones
(ketols) in the presence of a catalytic base
• Reaction is only possible between two components
having α-hydrogen
• Such reactions are reversible
• Mechanism: involves enolate formation and
nucleophilic attack at a carbonyl carbon
• Aldols and ketols loss water in the presence of an acid
forming α-ß-unsaturated aldehydes or ketones and ß-
hydroxy aldehydes or ketones

3. Aldol condensation
• Aldehydes containing α-hydrogen undergo self
addition in the presence of a base to form aldols
• For example
2 molecules of acetaldehyde condense to form
aldol haviving name 3 hydroxy butanal

5. Mechanism
Step-1 One carbonyl partner with an alpha hydrogen atom is
converted by base into its enolate ion.
O
H
C OH
R C

6. O Nucleophilic
OH2 Donor
C
: O:
R C:
Step 2 This enolate ion
C Electrophilic
acts as a nucleophilic Acceptor
donor and adds to the
electrophilic carbonyl
group of the acceptor
partner O ..
C O :
C ..
R C

7. OH2
O
C C
C OH -OH
R +
New C-C Bond
Step 3 addition of water resulting a neutral
condensation product.

8. Mechanism of the Aldol Reaction
O
HO:
Base removes an
H C
acidic alpha hydrogen C
from one aldehyde
H
molecule, yielding
a resonance-
H H
stabilized eno-
late ion.

9. O
: O: .. C + H2O
H
C C H
The enolate ion attacks
CH3 H H a second aldehyde
molecule in a
nucleophilic addition
reaction to give a
tetrahedral alkoxide ion
intermediate.

10. H 2O
Protonation of the alkoxide ion intermediate yields
neutral aldol product and regenerates the base
catalyst.

11. Aldols loss water in the presence of
an acid forming α-ß-unsaturated
aldehydes
Heat/acid

12. Ketol condensation
• Like aldehydes, ketones having alpha
hydrogen condense to form ketols
For example
2 molecules of acetone condense to produce
4-hydroxy, 4-methyl, 2-pentanone

13. 4-hydroxy, 4-methyl, 2-pentanone 4 methyl-3 pentene-2 one

14. Mixed aldol condensation
• If two different aldehydes condense, the
process is called mixed aldol condensation.
• For example
• Benzaldehyde and acetaldehyde condense
to form cinnamaldehyde