The sulfonic acid group is a strongly water-soluble strong acidic group. The sulfonic acid is a water-soluble strongly acidic compound. For example, naphthalene is soluble in ether and insoluble in water, while β-naphthalenesulfonic acid is soluble in water and insoluble in ether. The sulfonic acid group in the aromatic sulfonic acid molecule can be substituted by a hydroxyl group or a cyano group, and is an intermediate for preparing a phenol or a nitrile.
Used as analytical reagents, preservatives, bleaches and reducing agents.