Acid Catalysed Aldol Condensation

As we know, Condensation is an additional reaction in which two or more molecules combine to form a single molecule, eliminating small molecules like Water (H₂O), Ethanol (C₂H₅OH), or ammonia (NH₃). Let’s understand this in detail.

1.0Introduction to Condensation Reactions

Condensation reactions are a fundamental class of chemical reactions in organic and inorganic chemistry, where two molecules combine to form a larger molecule, with the simultaneous elimination of a smaller molecule such as water, alcohol, or hydrogen chloride.  

2.0What is Aldol Condensation Reaction? 

Aldehyde or Ketones having at least one α-H when treated with dilute alkali forms.

B-hydroxy carbonyl Compounds, Which further upon heating forms α, β–  unsaturated carbonyl compounds. 

Acid-Catalysed Aldol Condensation 

It is a chemical reaction where an enol or enolizable aldehyde or ketone undergoes a condensation reaction in the presence of an acid catalyst, resulting in the formation of a β-hydroxy aldehyde (aldol) or β-hydroxy ketone. This reaction can further lead to the formation of an α,β-unsaturated carbonyl compound upon dehydration.

Mechanism of acid-catalyzed aldol condition

Keto-Enol Tautomerism:

• Acid catalyzes the conversion of the keto form to the enol form, which acts as the nucleophile.

Activation of the Electrophile:

• Acid protonates the carbonyl oxygen of the aldehyde or ketone, making the conjugate acid a much better electrophile due to resonance stabilization.

Aldol Addition and Dehydration:

• The enol attacks the protonated aldehyde/ketone, forming a β-hydroxy carbonyl compound (aldol addition product).
• Protonation of the hydroxyl group converts it into water (H₂O), a good leaving group, leading to dehydration. This forms an α,β-unsaturated carbonyl compound via a "1,4-elimination" step.

Examples of Acid catalysed aldol condensation-