(A Level Chem) Synthesis of benzoic acid from toluene

During a Chemistry lecture in NUS, a sudden offensive stench of urine almost made me recoil as my friend appeared and sat beside me without warning. I tried to be polite to ask what that smell was but he ignored me. It was very odd. His face was expressionless oblivious to his smell. I couldn't tell whether he was angry about something or not. He just refused to speak. Not that he was not peculiar in his everyday manners, but he was different that day. I guessed something must had happened in the Organic Chemistry lab because most organic chemicals smell bad. I could not pin down what compound that was but I suspected the culprit was benzoic acid. I imagined that while he was heating a conical flask of the benzoic acid to make it dissolve in water, the flask broke and the benzoic acid solution spilled onto his pants. Well, it could be another compound but he never told me what happened.

The synthesis of benzoic acid is a must for all Chemistry undergraduates. In A Level however, it is just briefly learned in lectures. How is benzoic acid made in the lab?

Potassium permanganate oxidizes toluene to potassium benzoate...

We can oxidize toluene (methyl benzene) or propyl benzene to benzoic acid under reflux with alkaline potassium permanganate. During the reflux you'll see the purple color of potassium permanganate changes to dark brown ppt as the permanganate is reduced to manganese dioxide. At the same time, the alkyl benzene is oxidized to potassium benzoate which is soluble. The manganese dioxide ppt is then filtered away to obtain a filtrate of potassium benzoate solution. To precipitate out the benzoic acid, the mixture is then acidified with an acid. Finally, to get pure crystals of benzoic acid, we heat the mixture to dissolve the benzoic acid ppt and then leave the mixture to cool at room temperature for crystallization.

The color of permanganate changes to dark brown ppt of manganese dioxide...

Here's a thesis of the synthesis from 1919 just for your interest: http://share.iit.edu/bitstream/handle/10560/776/preparationofben00grig.pdf?sequence=1

Here's a video of the synthesis: https://www.youtube.com/watch?v=AvkWa8b_xdM