Write a note on electrophilic substitution reactions in the ring of aromatic carboxylic acids.

(N/A) $1$. Aromatic carboxylic acids undergo electrophilic substitution reactions.
$2$. The carboxyl group $(-COOH)$ acts as a deactivating and meta-directing group.
$3$. They do not undergo Friedel-Crafts reactions because the carboxyl group is strongly deactivating and the catalyst (Lewis acid,$AlCl_3$) gets bonded to the carboxyl group.
$4$. Examples:
$(i)$ Nitration of benzoic acid: Benzoic acid reacts with conc. $HNO_3$ and conc. $H_2SO_4$ to form $m$-nitrobenzoic acid.
(ii) Bromination of benzoic acid: Benzoic acid reacts with $Br_2$ in the presence of $FeBr_3$ to form $m$-bromobenzoic acid.
(iii) Sulphonation of benzoic acid: Benzoic acid reacts with $H_2SO_4$ (containing $SO_3$) to form $m$-sulphobenzoic acid.