Benzene and Alkyl Benzene - Result Question 35
39. Give reasons for the following :
(i) tert-butylbenzene does not give benzoic acid on treatment with acidic $KMnO _4$.
(ii) Normally, benzene gives electrophilic substitution reaction rather than electrophilic addition reaction although it has double bond.
(2000)
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Solution:
(i) Oxidation of side-chain alkyl group of benzene occur through free radical mechanism and it initiates at $\alpha-C$ as.
In tertiary butyl benzene, there is no $\alpha-H$, required to initiate free radical oxidation reaction, hence not oxidised with $KMnO _4$.
(ii) Pi-electrons of double bonds are involved in aromatic delocalisation (aromaticity), hence electrophilic addition do not occur as it would destroy aromatic stability. However, electrophilic substitution do not destroy aromaticity.
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