Does diatomic sulfur (S2) react as a free species?

Article abstract of DOI:10.1021/ja00030a048

A detailed study into the design and synthesis of stable 1,2-dithietane derivatives for the generation of diatomic sulfur (S₂) was undertaken. Computer-aided evaluation of enthalpic differences was used to direct the synthesis of target compounds and, although all of the compounds calculated to afford S₂ that were prepared did yield diatomic sulfur, an isolable 1,2-dithietane other than dithiatopazine failed to materialize. The results of this study provide convincing evidence that the computational procedure outlined can be successfully used to predict the course of S₂ extrusion pathways from potential dithionocarbonylated derivatives. To determine if the disulfide moiety found in the Diels-Alder adduct derived from the addition of diatomic sulfur to conjugated 1,3-dienes is due to a transference mechanism involving the transient 1,2-dithietane intermediate, a chiral nonracemic binaphthyl source of S₂ was prepared. Reactions of S₂ from this source with chiral nonracemic and prochiral conjugated 1,3-dienes indicate that the added disulfide moiety would be inconsistent with a transference mechanism and that a "free" acting S₂ unit is more likely to be involved.