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Side chain oxidation of aryl alkanes takes place if there is at least one alpha hydrogen present by all accounts I presumed that there would be no reaction. However the answer given was trimethyl acetic acid. Is the answer key wrong?

Gaurang Tandon
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Avyansh Katiyar
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A similar reaction with chromium oxide in alkaline solution has been documented.

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The acidic chromium oxide serves the same role as alkaline KMnO4 i.e a strong oxidizing agent. As pointed out by @Waylander in the comments permanganate oxidizes double bonds even in aromatic compounds.

Reference:
$\large{•}$ Chromium Oxidations in Organic Chemistry; By G. Cainelli, G. Cardillo

Avyansh Katiyar
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For reaction with $\ce{KMnO4}$, the given compound must have a carbon atom attached directly to the ring and that carbon atom must have at least one hydrogen atom. But in case of tert-butylbenzene this condition isn't followed and hence is a special case. The final product obtained on reaction of tert-butylbenzene with $\ce{KMnO4}$ is Pivalic acid $\ce{(CH3)3CCOOH}$ (Common name: Dimethylpropanoic acid).

Mathew Mahindaratne
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Swara.
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Under normal circumstances, kmno4 will not oxidise tertiary butyl benzene. However, under drastic conditions, oxidative cleavage of bonds occur and a mixture of acetic acid and trimethyl acetic acid is formed. Hence the answer is incorrect. They should have mentioned the word 'drastic conditions'.

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    What are "drastic conditions?" If something lives in the hydrocarbon lakes of Titan then liquid water would seem drastic to it. – Oscar Lanzi Sep 06 '20 at 13:53