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.

  • 1
    $\begingroup$ Possible duplicate of Oxidation of toluene to benzoic acid in presence of KMnO4 $\endgroup$
    – ringo
    Commented Feb 20, 2016 at 2:35
  • 1
    $\begingroup$ @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
    Commented 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
    Commented Feb 20, 2016 at 6:22

1 Answer 1


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.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.