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Question 43

Toluene can be easily converted into benzaldehyde by which of the following reagents?

Direct oxidation of toluene usually produces benzoic acid because strong oxidizing agents over-oxidize the methyl group.

Controlled oxidation using $$\mathrm{CrO_3}$$ in acetic anhydride $$\mathrm{((CH_3CO)_2O)}$$ prevents this over-oxidation.

The methyl group is first converted into the stable intermediate benzylidene diacetate.

This intermediate resists further oxidation.

Acid hydrolysis using $$\mathrm{H_3O^+}$$ then converts the intermediate into benzaldehyde $$\mathrm{(C_6H_5CHO)}$$.

Reagents such as $$\mathrm{KMnO_4}$$ directly oxidize toluene into benzoic acid $$\mathrm{(C_6H_5COOH)}$$.

The Gattermann-Koch reaction using $$\mathrm{CO/HCl/AlCl_3}$$ introduces a formyl group onto the aromatic ring rather than oxidizing the side chain.

Hence, the correct reagent sequence for conversion of toluene to benzaldehyde is Option $$\mathrm{(B)}$$.

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