Axial:Equatorial Rate Ratios and the Mechanism of Formation of Sulfenes by Dehydrohalogenation of Alkanesulfonyl Chlorides

Abstract

The method of axial:equatorial rate ratios has been applied to the study of the mechanism of formation of sulfenes via the reaction of alkanesulfonyl chlorides with base. The axial trans-2-decalinsulfonyl chloride (6) and the equatorial trans-2-decalinsulfonyl chloride (8) were synthesized. The axial sulfonyl chloride 6 was found to react 71 times faster than the equatorial epimer 8 with triethylamine in the presence of aniline at −25°, a reaction which evidently proceeds via the sulfene 7. With water at 50° without added base (a reaction believed to take place by direct attack on the sulfur atom) 8 reacts about 14 times faster than 6. It is concluded that the formation of the sulfene 7 from 6 by the action of triethylamine cannot take place by a mechanism involving a slow S_N2 reaction followed by a fast bimolecular elimination, and that the most likely route for 6, and other alkanesulfonyl chlorides as well, is the E2 reaction.