Moderate

Which compound form benzoic acid on oxidation with acidified KMnO4 or K2Cr2O7 ?

Correct answer: D. All

  • A. Toluene
  • B. Ethyl benzene
  • C. n-propyl benzene
  • D. All

Explanation

Strong oxidation of an alkylbenzene with acidified KMnO4 or K2Cr2O7 converts the entire side chain into a carboxyl group, provided the side chain has at least one benzylic hydrogen. Toluene, ethylbenzene and n-propylbenzene all meet this condition, giving benzoic acid. Students may select only toluene by overlooking that longer side chains are also oxidised at the benzylic carbon.

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Benzene has a planar ring of delocalised π electrons, giving aromatic stability and equal carbon-carbon bond lengths. The topic covers resonance, electrophilic substitution reactions such as nitration, halogenation, sulphonation and Friedel-Crafts reactions, along with substituent effects and the distinction between substitution in benzene and addition in ordinary alkenes.

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