Aldol Condensation Reaction

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

Aldol Condensation Reaction

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
Aldol Condensation Reaction bita-hydroxyaldehyde and  bita-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.

acidic in nature of alpha hydrogen of carbonyl compounds

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.

Reaction Mechanism of Aldol Condensation reaction

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:

  1. What is aldol condensation?
  2. Explain the mechanism of aldol condensation.
  3. How to do this condensation reactions ?

For a better understanding of this concept, use the book or Internet Web Page

  1. Organic Chemistry by Morrison & Boyd
  2. Organic Chemistry written by Solomons & Fryhle
  3. A l d o l condensation – Wikipedia
  4. A l d o l Condensation – Chemistry LibreTexts
  5. A l d o l Condensation – UCLA Chemistry

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