Acetal Formation
Easychemistry
Acetal formation from aldehyde and alcohol is catalyzed by:
Select the correct option:
Solution
Incorrect! Answer:
Dilute acid (protonic)
- Requirement: To form an acetal (R−CH(OR′)2), two molecules of alcohol must add to one molecule of aldehyde.
- Mechanism Step 1: The Carbonyl Oxygen is protonated by an acid catalyst (e.g., dry HCl gas or p−TsOH).
- Significance: This makes the carbonyl Carbon much more electrophilic, allow the weak nucleophile (alcohol) to attack.
- Hydration Barrier: After forming the hemiacetal, acid is again required to protonate the −OH group, making it a good leaving group (H2O) for the second alcohol attack.
- Base contrast: In base, hemiacetals can form but full acetals generally do not because the −OH group cannot be displaced as OH− by another OR− nucleophile.
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About This Question
- Subject
- chemistry
- Chapter
- oxygen organics
- Topic
- acetal formation
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
Dilute acid (protonic)
- Requirement: To form an acetal (R−CH(OR′)2), two molecules of alcohol must add to one molecule of aldehyde.
- Mechanism Step 1: The Carbonyl Oxygen is protonated by an acid catalyst (e.g., dry HCl gas or p−TsOH).
- Significance: This makes the carbonyl Carbon much more electrophilic, allow the weak nucleophile (alcohol) to attack.
- Hydration Barrier: After forming the hemiacetal, acid is again required to protonate the −OH group, making it a good leaving group (H2O) for the second alcohol attack.
- Base contrast: In base, hemiacetals can form but full acetals generally do not because the −OH group cannot be displaced as OH− by another OR− nucleophile.
This easy difficulty chemistry question is from the chapter oxygen organics, covering the topic of acetal formation. It appeared in the 2025 exam.
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