Question

Which of the following pairs do not give the same compound on heating with alkaline potassium permanganate?

(a) Toluene and propyl benzene

(b) Toluene and n-Butyl benzene

(c) Propyl benzene and isopropyl benzene

(d) o-Xylene and n-Butyl benzene

I got this question by my college professor while I was bunking the class.

Enquiry is from Methods of Carboxylic Acids Preparation topic in chapter Aldehydes, Ketones and Carboxylic Acids of Chemistry – Class 12

Answer 1

The correct option is (d) o-Xylene and n-Butyl benzene

For explanation: All mono-substituted alkyl benzenes, with primary or secondary alkyl groups, on vigorous oxidation give benzoic acid. The entire side chain is oxidised irrespective of the length. In case of o-xylene, there are two methyl groups on the benzene ring and both of them are oxidised to carboxyl group, resulting in phthalic acid.