Write a note on the preparation of carboxylic acid from alkyl benzene.

(N/A) Aromatic carboxylic acids can be prepared by the vigorous oxidation of alkyl benzenes with chromic acid or acidic/alkaline potassium permanganate $(KMnO_4)$.
$(a)$ The entire side chain is oxidized to the carboxyl group $(-COOH)$ irrespective of the length of the side chain,provided that the benzylic carbon atom has at least one hydrogen atom.
$(b)$ Primary and secondary alkyl groups are oxidized to the carboxyl group in this manner.
$(c)$ If the benzylic carbon atom does not have any hydrogen atom (i.e.,tertiary alkyl group),then oxidation is not possible.
$(d)$ The reaction proceeds via the formation of a potassium salt (e.g.,potassium benzoate),which upon acidic hydrolysis $(H_3O^+)$ yields the corresponding aromatic carboxylic acid.
General reaction:
$C_6H_5-CH_2-R$ $\xrightarrow[\Delta]{KMnO_4, KOH} C_6H_5-COOK$ $\xrightarrow{H_3O^+} C_6H_5-COOH$