What is the major product obtained when acetaldehyde (CH3CHO) is treated with dilute sodium hydroxide solution and subsequently heated?
Answer and explanation
Correct answer: D. But-2-enal (Crotonaldehyde, CH3-CH=CH-CHO)
- Step 1: Acetaldehyde contains -hydrogens. Treatment with dilute generates an enolate ion: .
- Step 2: The enolate attacks another acetaldehyde molecule to form the aldol intermediate: 3-hydroxybutanal ().
- Step 3: Upon heating, 3-hydroxybutanal undergoes spontaneous dehydration (loss of a water molecule) driven by the formation of an extended conjugated -system.
- Step 4: This yields the -unsaturated aldehyde but-2-enal (crotonaldehyde: ).
Answer
But-2-enal (Crotonaldehyde, CH3-CH=CH-CHO)
Why not the others: '3-Hydroxybutanal (Aldol)' is the unheated initial aldol product, but heating forces dehydration to but-2-enal; 'Butan-1-ol' is a complete reduction product; 'Ethyl acetate' is the product of the Tishchenko reaction with aluminum ethoxide.
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