Answer: CrO3 in acetic anhydride.
- A CrO3 in acetic anhydride
- B Cl<sub>2</sub> gas under UV light via free-radical chlorination
- C Hot alkaline KMnO<sub>4</sub>, which oxidises all the way to benzoic acid
- D Aqueous NaOH under reflux
Correct answer: A. CrO3 in acetic anhydride
Explanation: The Etard reaction or chromyl chloride (CrO3 in acetic anhydride) oxidises the methyl side chain to -CHO.
Curved arrows show the nucleophile attacking the carbonyl carbon while the C=O pi electrons move onto oxygen, giving a tetrahedral alkoxide intermediate.
Concept context
Aldehydes, ketones, carboxylic acids, and their derivatives (esters, amides, acid chlorides). Key reactions include nucleophilic addition, Aldol condensation, Cannizzaro, and Claisen. Very heavily tested in JEE and NEET.
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