Sulfonic acid
Sulfonic acids contain R–SO₃H. Learn their structure, nomenclature, acidity, sulfonates, and applications.
Functional group
How to name it with IUPAC
Use “sulfonic acid” after the parent chain or aryl group. C₆H₅SO₃H is benzenesulfonic acid; CH₃SO₃H is methanesulfonic acid.
Properties and applications
The sulfonic group has three oxygens and is strongly polar. Most sulfonic acids are strong acids in water; their salts, sulfonates, are important surfactants.
Characteristic reaction
Neutralization forms sulfonates. Aromatic sulfonation introduces –SO₃H into a ring and can be reversible depending on conditions; sulfonate derivatives can also be excellent leaving groups.
Examples
Methanesulfonic acid (CH₃SO₃H) · Benzenesulfonic acid (C₆H₅SO₃H) · p-Toluenesulfonic acid
A sulfonic acid R–SO₃H is not sulfuric acid H₂SO₄ or a sulfate R–OSO₃H. In R–SO₃H, sulfur is directly bonded to carbon.