Sulphonation of Aniline (Zwitterion Formation)

$$\begin{aligned}\text{C}_6\text{H}_5\text{NH}_2 + \text{Conc. H}_2\text{SO}_4 \to \text{C}_6\text{H}_5\text{NH}_3^+\text{HSO}_4^- \xrightarrow{453\text{--}473\text{ K}} p\text{-Aminobenzenesulphonic acid (Sulphanilic Acid)}\end{aligned}$$

$$\begin{aligned}\text{Sulphanilic Acid Structure: } \text{H}_2\text{N--C}_6\text{H}_4\text{--SO}_3\text{H} \rightleftharpoons \text{H}_3\text{N}^+\text{--C}_6\text{H}_4\text{--SO}_3^- \quad (\text{Zwitterion})\end{aligned}$$