Dialkyl disulfide ions

Modena and et al. concluded, on the basis of experimental evidence, that nucleophilic substitution at thiiranium and thiirenium sulfur is sensitive to substituents, and that dialkyl disulfides approach the sulfur in a perpendicular sense, not in the collinear sense shown as the a -direction in 219 see also Section 1.05.8.3 <1999JA3944, 2000CEJ589>. Their rationale for the apparent difference between experimental and theoretical substitution mechanisms focused on bicentric versus monocentric nucleophiles. The former attack thiiranium ions in the 3c-direction and the latter in the y-direction. Radom s group disagrees on the basis of theory <1998JA7063, 2000CEJ590>. 

Mixed disulfides can be synthesized by the reaction of alkyldithioformic esters with thiols (95) through a soft-soft interaction. However, attempts to extend the reaction to prepare sulfenate esters using alkoxides as nucleophiles led to dialkyl trisulfides (96) instead. If a H8AB analysis was performed prior to experiments, the authors would not have been surprised by the results. The hard alkoxide ions would of course elect to attack the ester carbonyl. 

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