In the self-aldol condensation of ethanal (acetaldehyde) catalyzed by dilute aqueous followed by heating, what is the final dehydrated organic product?
Answer and explanation
Correct answer: B. But-2-enal
- Step 1: In the presence of dilute base, an enolate ion generated from ethanal attacks another ethanal molecule to form the aldol intermediate: (3-hydroxybutanal).
- Step 2: Upon heating, the -hydroxy aldehyde undergoes base-catalyzed dehydration (E1cB mechanism) by losing a molecule of water.
- Step 3: This produces a stable, conjugated -unsaturated aldehyde: (but-2-enal, commonly known as crotonaldehyde).
Answer
But-2-enal (crotonaldehyde).
Why not the others: 3-Hydroxybutanal is the aldol intermediate prior to heating and dehydration; But-1-en-3-one is methyl vinyl ketone derived from acetone and formaldehyde; Butanoic acid is a fully oxidized carboxylic acid.
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