Question

Which of the following cannot be converted to benzoic acid on reaction with KMnO4-KOH followed by H3O^+?

(a) Ethyl benzene

(b) Acetophenone

(c) 4-Methylacetophenone

(d) Styrene

I had been asked this question by my school teacher while I was bunking the class.

My question comes from Methods of Carboxylic Acids Preparation in section Aldehydes, Ketones and Carboxylic Acids of Chemistry – Class 12

Answer 1

Right answer is (c) 4-Methylacetophenone

Easiest explanation: The ethyl group, acetyl group and ethene group are all oxidised to potassium carboxylate groups which are further oxidised to carboxyl groups. In the case of 4-Methylacetophenone, there are two groups that will be oxidised to carboxyl groups, hence forming terephthalic acid instead of benzoic acid.