Reagent Selectivity
Hardchemistry
Selective oxidation of secondary alcohol to ketone without affecting primary alcohol in same molecule uses:
Select the correct option:
Solution
Incorrect! Answer:
PCC (CH2Cl2)
- Oxidation comparison:
- KMnO4,HNO3 and Jones reagent are very strong oxidants. They will oxidize primary alcohols all the way to carboxylic acids and secondary alcohols to ketones.
- PCC is milder.
- Selectivity Factor: While both positions are oxidized to carbonyls by PCC, in manual synthesis, controlling stoichiometric amounts or utilizing slightly different reaction rates can favor one.
- Correct Context: PCC is particularly useful because it does not over-oxidize the primary alcohol. In a complex molecule, using 1 equivalent of PCC in anhydrous dichloromethane allows for precise control, typically yielding the aldehyde/ketone without degrading other sensitive oxy-functional groups unlike the more aggressive aqueous acidic reagents.
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About This Question
- Subject
- chemistry
- Chapter
- oxygen organics
- Topic
- reagent selectivity
- Difficulty
- Hard
- Year
- 2025
Solution
Correct Answer:
PCC (CH2Cl2)
- Oxidation comparison:
- KMnO4,HNO3 and Jones reagent are very strong oxidants. They will oxidize primary alcohols all the way to carboxylic acids and secondary alcohols to ketones.
- PCC is milder.
- Selectivity Factor: While both positions are oxidized to carbonyls by PCC, in manual synthesis, controlling stoichiometric amounts or utilizing slightly different reaction rates can favor one.
- Correct Context: PCC is particularly useful because it does not over-oxidize the primary alcohol. In a complex molecule, using 1 equivalent of PCC in anhydrous dichloromethane allows for precise control, typically yielding the aldehyde/ketone without degrading other sensitive oxy-functional groups unlike the more aggressive aqueous acidic reagents.
This hard difficulty chemistry question is from the chapter oxygen organics, covering the topic of reagent selectivity. It appeared in the 2025 exam.
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