Sulfenamide

Sulfenamides (also spelled sulphenamides) are a class of organosulfur compounds characterized by the general formula RSNR'₂, where R and R' are H, alkyl, or aryl. Sulfenamides have been used extensively in the vulcanization of rubber using sulfur. They are related to the oxidized compounds sulfinamides (RS(O)NR'₂) and sulfonamides (RS(O)₂NR'₂).

Sulfenamides are usually prepared by the reaction of sulfenyl chlorides and amines:

The S-N bond formation generally obeys standard bimolecular nucleophilic substitution rules, with the basic nitrogen centre being the nucleophile. Primary sulfenamide formation as shown above occurs with the reaction of the sulfenyl halide with ammonia. Additionally primary as well as secondary and tertiary amines form sulfenamides through reaction with, thiols, disulfides, and sulfenyl thiocyanates. In one illustrative synthesis, triphenylmethanesulphenyl chloride and butylamine react in benzene at 25 C:

Many other routes to sulfenamides are known, starting from thiols and disulfides.

Sulfenamides have been characterized by X-ray crystallography. The S-N bond in sulfenamides is a chiral axis that leads to formation of diastereomeric compounds. The existence of these distinct stereoisomers is due to the formation of a partial double bond between either sulfur or nitrogen’s lone pair and the other atom’s antibonding orbitals. Additionally bulky substituent groups and lone pair repulsion can contribute resistance to interconversion. The resulting torsional barriers can be quite large and vary from 12-20 kcal/mol. The interactions are thought to be dependent on the torsional preferences (also known as the gauche effect). The nitrogen atom is usually pyramidal, but cyclic and strongly steric hindered acyclic sulfenamides can display a planar arrangement of bonds around the nitrogen atom.

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