The structure of a typical sulfonate ion.
A sulfonate is a salt or ester of a sulfonic acid. It contains the functional group R-SO 2 O-.
Anions with the general formula RSO 2 O −
are called sulfonates. They are the conjugate bases of sulfonic acids with formula RSO 2 OH. As sulfonic acids tend to be strong acids, the corresponding sulfonates are weak bases. Due to the stability of sulfonate anions, the cations of sulfonate salts such as scandium triflate have application as Lewis acids.
A classic organic reaction for the preparation of sulfonates is that of alkyl halides with sulfites such as sodium sulfite, first described by Adolph Strecker in 1868 (Strecker sulfite alkylation).  The general reaction is:
RX + M 2 SO 3 → RSO 3 M + MX
Iodide is used as a catalyst.
Esters with the general formula R 1 SO 2 OR 2 are as a category called sulfonic esters. Individual members of the category are named analogously to how ordinary carboxyl esters are named. For example, if the R 2 group is a methyl group and the R 1 group is a trifluoromethyl group, the resulting compound is methyl trifluoromethanesulfonate.
Sulfonic esters are used as reagents in organic synthesis, chiefly because the RSO 2 O- group is a good leaving group in Sn1, Sn2, E1 and E2 reactions. Methyl triflate, for example, is a strong methylating reagent. They are commonly used to lend water solubility to protein crosslinkers such as N-hydroxysulfosuccinimide (Sulfo-NHS), BS3, Sulfo-SMCC, etc.
Cyclic sulfonic esters are called sultones.  One example is 1,3-propane sultone. Some sultones are short-lived intermediates, used as strong alkylating agents to introduce a negatively charged sulfonate group. In the presence of water, they slowly hydrolyze to the hydroxy sulfonic acids. Sultone oximes are key intermediates in the synthesis of the anti-convulsant drug zonisamide. 
Mesylate (methanesulfonate), CH 3 SO 2 O-Triflate (trifluoromethanesulfonate), CF 3 SO 2 O-Esylate (ethanesulfonate), C 2 H 5 SO 2 O-
Besylate (benzenesulfonate), C 6 H 5 SO 2 O-Tosylate (p-toluenesulfonate), CH 3 C 6 H 4 SO 2 O-