Question

Explain Aldol condensation of ethanal.

Hint:

Aldol condensation reactions are widely used in organic synthesis to form carbon-carbon bonds, particularly in the synthesis of α,β-unsaturated carbonyl compounds.

Answer 1

The Aldol Condensation is a reaction in which an enolate ion attacks the carbonyl carbon of an aldehyde or ketone to form a β-hydroxy aldehyde or ketone, which then undergoes dehydration to form an α,β-unsaturated carbonyl compound. Step 1: Aldol Addition Reaction.
When ethanal (acetaldehyde, \(CH_3CHO\)) undergoes the Aldol addition, the enolate ion formed from one molecule of ethanal reacts with another molecule of ethanal: \[ CH_3CHO + CH_3CHO \xrightarrow{OH^-} CH_3CH(OH)CH_2CHO \] This forms β-hydroxybutanal, also known as an Aldol addition product. Step 2: Dehydration to form Aldol Condensation Product.
The β-hydroxy aldehyde undergoes elimination of water, resulting in the formation of an α,β-unsaturated aldehyde: \[ CH_3CH(OH)CH_2CHO \xrightarrow{heat} CH_3CH=CHCHO \] This product, crotonaldehyde, is the result of the Aldol condensation.