Phenol From Benzene Sulfonic Acid:

$$\text{C}_6\text{H}_5\text{SO}_3\text{H} \xrightarrow{\text{1) NaOH, } \Delta \quad \text{2) H}^+} \text{Phenol}$$

Concept

Benzene sulfonic acid is neutralized with base to yield sodium benzenesulfonate, which undergoes alkali fusion with molten sodium hydroxide at high temperatures ($$\sim 573\text{ K}$$) to displace the sulfonate group. Acidification of the resulting sodium phenoxide salt yields phenol.