write a note on Aldol condensation
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Write a note on 'aldol condensation'.
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'Aldol condensation' :
This reaction is given by aldehydes or ketones having alpha hydrogen atom. The alpha hydroge atom is acidic in nature. In presence of dil NaOH/KOH or Na
2
CO
3
, two molecules of an aldehdye or ketone add to form beta hydroxy aldehdye (aldol) or beta hydroxy ketone (ketol).
The name aldol represents two functional groups, 'al' for aldehdye and 'ol' for alcohol. During the reaction, one aldehyde molecule acts as a nucleophile and adds to second molecule. Alpha C atom of first molecule is attached to carbonyl carbon of second molecule. A C−C bond is formed.
When aldol (or ketol) is heated in presence of acid or base, it undergoes dehydration to form alpha-beta unsaturated aldehdye or ketone.
2(CH
3
)
2
C=O+dilNaOH⇌(CH
3
)
2
C(OH)−CH
2
−C(=O)−CH
3
Δ
(CH
3
)
2
C=CH(=O)−CH
3
Aldol condensation: In the presence of a dilute alkali, aldehydes and ketones (having at least one α-hydrogen atom) produce β-hydroxyl aldehyde (aldol) and β-hydroxyl ketone respectively. The aldol and ketol then readily lose water to give α, β-unsaturated carboxyl compounds. Such reactions are called aldol condensation. For example, in the presence of dil. NaOH, ethanal (aldehyde) produces 3-hydroxybutanal (aldol), which then readily loses water to produce but-2-enal.
