Tosyl
Encyclopedia : T : TO : TOS : Tosyl
A tosyl group (abbreviated Ts) combines the toluene and sulfonyl functional groups. A sulfonyl group consists of a hexavalent sulfur atom double bonded to two oxygen atoms and an aromatic ring; an alkyl substitutent on the R group forms a sulfonate ester. Thus, the tosylate group is the ester of toluenesulfonic acid. The para orientation illustrated (p-toluenesulfonyl) is most common, and by convention tosyl refers to the p-toluenesulfonate ester.
A tosylate ester has only a limited shelf life if it is stored outside of a desicator as the free tosyl is readily broken by light and water. The tosyl group is electron-withdrawing.
The tosyl group is a protecting group for alcohols, prepared by combining the alcohol with toluenesulfonyl chloride in an aprotic solvent. Toluenesulfonyl chlorides activate alcohols for nucleophilic attack or elimination (dehydration).
Similarly, the brosyl (Bs) group or brosylate is a p-bromobenzenesulfonyl group with the methyl group of toluene replaced by a bromine atom. Nosyl groups in Nosylates (Ns) are 2-nitrobenzenesulfonyl groups with a nitro group in the ortho position.
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