Sulfonates

Sulfonates are a class of chemical entities derived from sulfonic acids. They include both salts of sulfonic acids, with the general formula R-SO3− balanced by a counterion such as Na+, K+, or an ammonium group, and sulfonate esters, which form when the sulfonyl group is bound to an alkoxy or aryloxy moiety (commonly written as RO-SO2-R'). The R group can be alkyl or aryl, and the sulfonate group bears three oxygens arranged around sulfur.

Common sulfonate esters arise from alcohols reacting with sulfonylating agents. Notable examples are tosylates (p-toluenesulfonates), mesylates (methanesulfonates), and triflates (trifluoromethanesulfonates). In practice, alcohols are converted to these derivatives to improve leaving-group ability in organic reactions. Commercially used sulfonate chlorides or anhydrides (such as TsCl, MsCl, or Tf2O) enable synthesis of the corresponding alkyl sulfonates under basic conditions.

Properties and applications vary with the substituents. Sulfonate esters are typically stable to neutral conditions but can be cleaved by nucleophiles under appropriate conditions, making them excellent leaving groups for substitutions and eliminations in organic synthesis. Triflate esters, in particular, are among the best leaving groups known. Sulfonates also occur as detergents and surfactants in the form of alkyl sulfonates and aryl sulfonates.

Safety and handling depend on the specific compound. Sulfonyl chlorides used to prepare sulfonates are typically corrosive and lachrymatory; appropriate precautions are advised.