Sulfonate

The structure of a typical sulfonate group.

A sulfonate ion is an ion that contains the -S(=O)₂-O⁻ functional group. The general formula is RSO₂O⁻, where R is some organic group. They are conjugate bases of sulfonic acids with formula RSO₂OH.

Sulfonates, being weak acids, are good leaving groups in Sn1, Sn2, E1 and E2 reactions.

As is common, the same term is used for compounds containing this functional group, ionic salts, or similar covalent compounds, esters.

Examples

• Mesylate (methanesulfonate) ion, CH₃SO₂O⁻
• Triflate (trifluoromethanesulfonate) ion, CF₃SO₂O⁻
• Tosylate (p-toluenesulfonate) ion, CH₃C₆H₄SO₂O⁻
• Besylate (benzenesulfonate) ion, C₆H₅SO₂O⁻

The preceding terms apply to salts and esters as well as anions.