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A question in my textbook:

Though alkaline and acidic $\ce{KMnO4}$ are both oxidizing agents, in the manufacture of benzoic acid from toluene, we only use alcoholic $\ce{KMnO4}$ as an oxidant. Why?

I am not able to figure out the answer. But I think maybe the acidic and alkaline $\ce{KMnO4}$ are too strong and may oxidize the benzene ring. Or the benzoic acid may react with the alkaline medium. (Though I wonder why it wouldn't react with alcohol to give ester)

I also tried digging around the web but couldn't come up with anything satisfactory.

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    $\begingroup$ Possible duplicate of Oxidation of toluene to benzoic acid in presence of KMnO4 $\endgroup$
    – ringo
    Feb 20, 2016 at 2:35
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    $\begingroup$ @ringo Not sure if this is a duplicate or not. Title and wording of the question refer to alcoholic $\ce{KMnO4}$, which is not what the linked question is about. Or, perhaps alcoholic is a typo in biogirl's blockquote? $\endgroup$
    – hBy2Py
    Feb 20, 2016 at 3:11
  • $\begingroup$ @ringo I guess my question is a duplicate. I just went through the question but the answer given was not satisfactory. $\endgroup$
    – biogirl
    Feb 20, 2016 at 6:22

1 Answer 1

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Practical considerations, mainly that toluene is non-polar, inorganic. Aqueous $\ce{KMnO4}$ wouldn't be miscible so the oxidation can only take place in the interface. By using alcoholic $\ce{KMnO4}$, we can get the $\ce{KMnO4}$ into the organic layer much more easily, thus making the reaction much faster.

To form an ester, you generally need a dehydrating environment. Plus, the oxidation of toluene with $\ce{KMnO4}$ in neutral conditions will produce base which neutralizes the benzoic acid, thus deactivating it making it unable to undergo esterification.

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