Sulfur-nitrogen cyclic anions

R. P. Sharma and R. D. Vetma, Recent Developments in the Chemistry of Sulfur-Nitrogen Compounds Sulfur-Nitrogen Cyclic Anions, J. Sci. Ind. Res., 40, 34 (1981). 

Sulfur and nitrogen form a variety of binary anions with acyclic, cyclic and cage structures.69,70 The Se-N anions are only known in metal complexes. S-N anions play an important role in the formation of cyclic sulfur imides and as constituents of solutions of sulfur in liquid ammonia. 

Role of Sulfur-Nitrogen Anions in the Synthesis of Cyclic Sulfur... 

The cyclic sulfur imides S NH and 1,3-, 1,4-, and l,5-S(j(NH)2 are obtained by acid hydrolysis of the deep blue intermediate formed from the reaction of SjClj with ammonia in polar solvents, e.g. DMF or by the reaction of sodium azide with elemental sulfur in HMPA The blue chromophore formed in both these reactions is S4N and it has therefore been suggested that this anion is involved in equilibria with cyclic sulfur-nitrogen anions which are the precursors of the imides... 

Sulfur and nitrogen represent a versatile combination in the formulation of binary anions with cyclic, cage, or catenated structures, none of which have counterparts among the known N-0 anions. In addition, several S-N anions are known only in complexes with transition metals (see Section 8.5). 

Like sulfur mustard, the nitrogen mustards combine predominantly with the thiol group of molecules and are excreted as conjugated cysteinyl derivatives. Both nitrogen and sulfur mustards have structural similarities and have common chemical reactions. A key reaction is the intramolecular cyclization in a polar solvent such as water to form a cyclic onium cation and a free anion. Nitrogen mustards form the immonium cation, while the sulfur mustard forms the sulfonium cation. The cyclized form is responsible for the varied effects of mustards, which are similar. In nitrogen mustard the sulfur is replaced by nitrogen. 

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