sulphonate

Sulphonate is a term used for salts or esters derived from sulfonic acids. The core feature is the sulfonate group, −SO3−, attached to an organic moiety (RSO3−) or forming the sulfonate ester RSO2OR'. Sulfonic acids (R-SO3H) are strong acids; in water they are almost completely dissociated, and sulphonates exist as their conjugate bases or as sulfonate esters.

In organic synthesis, sulfonate esters serve as versatile leaving groups. They are formed by reaction of sulfonyl chlorides (RSO2Cl) with alcohols, producing esters such as RSO2OR'. Common examples include tosylate (p-toluenesulfonate, TsO−), mesylate (MsO−), and triflate (trifluoromethanesulfonate, TfO−). These groups are excellent leaving groups, enabling substitutions and eliminations under mild conditions.

Sulphonates are widely used in industry and biology. Salts of sulfonates, such as alkyl or aryl sulfonates, serve as surfactants (for example, alkylbenzene sulfonates) and water-soluble dyes. In biochemistry, sulfonate groups occur in many molecules, including sulfonated polysaccharides and proteins, contributing negative charge and hydrophilicity. The term is often encountered in naming sulfonate esters, such as tosylates and mesylates, which are common reagents for protecting or activating alcohols in synthesis. See also sulfonic acid, sulfonate group, sulfonation.