The tosyl group with a generic 'O-R' group attached

Ball-and-stick model of the tosylate anion

A tosyl group (abbreviated Ts or Tos) is CH₃C₆H₄SO₂. This group is usually derived from the compound 4-toluenesulfonyl chloride, CH₃C₆H₄SO₂Cl, which forms esters and amides of toluenesulfonic acid. The para orientation illustrated (p-toluenesulfonyl) is most common, and by convention tosyl refers to the p-toluenesulfonyl group. Tosylate refers to the anion of p-toluenesulfonic acid (CH₃C₆H₄SO₃^-).

A tosylate ester has a limited shelf life in air due to its ready hydrolysis in the presence of light. The tosyl group is electron-withdrawing which makes tosylates excellent leaving groups. The tosyl group is also a protecting group for alcohols and amines, prepared by combining the alcohol with 4-toluenesulfonyl chloride, usually in an aprotic solvent, often pyridine, the basicity of which activates the reaction^[1]. Toluenesulfonate esters undergo nucleophilic attack or elimination.

A similar group is brosyl, "Bs" or brosylate (p-bromobenzenesulfonyl) group wherein the methyl group of toluene is replaced by a bromide. Nosyl groups in nosylates, "Ns", are 4-nitrobenzenesulfonyl groups with a nitro group in the para position, "Nps" stands for 2-nitrobenzenesulfonyl.

[edit] Applications

The use of these functional groups is exemplified in organic synthesis of the drug tolterodine, wherein one of the steps a phenol group is protected as its tosylate and the primary alcohol as its nosylate. The latter is a leaving group for displacement by diisopropylamine ^[2][3]:

[edit] References