Sulfonate

A sulfonate is a salt or ester of a sulfonic acid. It contains the functional group R-SO₃⁻.

Anions with the general formula RSO₃⁻ are called sulfonates. They are the conjugate bases of sulfonic acids with formula RSO₂OH. 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:

Iodide is used as a catalyst.

Esters with the general formula R¹SO₂OR² are called sulfonic esters. Individual members of the category are named analogously to how ordinary carboxyl esters are named. For example, if the R² group is a methyl group and the R¹ group is a trifluoromethyl group, the resulting compound is methyl trifluoromethanesulfonate.

Sulfonic esters are used as reagents in organic synthesis, chiefly because the RSO₃⁻ group is a good leaving group, especially when R is electron-withdrawing. Methyl triflate, for example, is a strong methylating reagent.

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