Aldol Condensation Reaction
An aldol condensation is a condensation reaction in which an enol or an enolate ion reacts with a carbonyl compound to form a β-hydroxyaldehyde or β-hydroxyketone (an aldol reaction), followed by dehydration to give a conjugated enone.
Aldol condensations are important in organic synthesis, because they provide a good way to form carbon–carbon bonds
This reaction is shown by aldehydes and Ketones having alpha-hydrogen atom in the compound. Such alpha-hydrogen atom containing aldehydes and ketones will undergo self condensation in presence dilute alkalies like dil NaOH, dil KOH, Ba(OH)2 etc.
- In presence of dilute alkalies two acetaldehyde react with each other to form β-hydroxyaldehyde
- In presence of dilute alkalies two acetone react with each other to form β-hydroxyketone
Why is alpha hydrogen in aldehyde, ketone ore in any carbonyl Compound more acidic in nature?
Alpha hydrogen is nothing but the hydrogen atom attached to the alpha carbon atom,which in turn is attached to the carbonyl carbon. After removal of alpha hydrogen atom, conjugated base so obtained is resonance stabilised. Hence alpha hydrogen atoms in aldehydes and ketones are acidic in nature.
As alpha hydrogen is acidic,bases can easily remove acidic hydrogen to form intermediate carbanions.
Reaction Mechanism of Aldol Condensation
The first part of this reaction is an aldol reaction, the second part a dehydration—an elimination reaction (Involves removal of a water molecule or an alcohol molecule). Dehydration may be accompanied by decarboxylation when an activated carboxyl group is present. The aldol addition product can be dehydrated via two mechanisms; a strong base like potassium t-butoxide, potassium hydroxide or sodium hydride in an enolate mechanism, or in an acid-catalyzed enol mechanism. Depending on the nature of the desired product.
Crossed Aldol Condensation
Claisen Schmidt Reaction
Sample Questions of Aldol Condensation Reactions
Some frequently asked questions in aldol condensation reaction that may help you in exam preparation are as follows:
- What is aldol condensation?
- Explain the mechanism of aldol condensation.
- How to do this condensation reactions ?