Although strong, the (aryl)C−SO bond can be broken by nucleophilic reagents. Of historic and continuing significance is the α-sulfonation of anthroquinone followed by displacement of the sulfonate group by other nucleophiles, which cannot be installed directly. An early method for producing phenol involved the base hydrolysis of sodium benzenesulfonate, which can be generated readily from benzene.
:CHSONa + NaOH → CHOH + NaSO
The conditions for this reaction are harsh, however, requiring fused alkali or molten sodium hydroxide at 350 °C for benzenesulfonic acid itself.  Unlike the mechanism for the fused alkali hydrolysis of chlorobenzene, which proceeds through elimination-addition (benzyne mechanism), benzenesulfonic acid undergoes the analogous conversion by an SAr mechanism, as revealed by a C labeling, despite the lack of stabilizing substituents.  Sulfonic acids with electron-withdrawing groups (e.g., with NO or CN substituents) undergo this transformation much more readily.