Question

How do you convert the following?
Toluene to Benzoic acid.

Answer 1

Hint: We need to understand the structure of the given compounds and understand the conversion accordingly. Toluene is an aromatic hydrocarbon. It has a methyl group attached to a phenyl group (benzene ring) hence it is also known as methylbenzene. Benzoic acid is also an aromatic hydrocarbon consisting of a carboxyl group attached to a benzene ring. Hence we need to study the conversion of a phenyl compound to an aromatic carboxylic acid.

Complete answer:
As we know that toluene is a methyl group added to a benzene ring and benzoic acid is a carboxyl group added to a benzene ring. Their structures are given below:

Given,Diagram of toluene and benzoic acid respectively.
It is clear from the structures that toluene has to be oxidised to produce benzoic acid. The conversion steps are given below:
-We have to remember when toluene is mixed with alkaline potassium permanganate ($KMnO_4$) which acts as the oxidizing agent. The mixture is heated and toluene is converted to potassium benzoate ions.
-This is followed by the acidification of potassium benzoate ions to produce benzoic acid. This acidification is carried out by dilute acids such has dilute hydrochloric acid (dil. HCl).
The overall reaction is given below:

Note:
We must be noted that this process is a simple oxidation of toluene to benzoic acid. This reaction is specifically carried out in an alkaline medium because strong oxidizing agents such as potassium permanganate are stable only under alkaline conditions and hence acid is added to later neutralize the alkalinity which converts the potassium benzoate ion to benzoic acid. Under neutral or acidic medium, the potassium permanganate becomes unstable and less powerful as an oxidizing agent.