Dithietane

1,2-dithietanes, 4-membered rings where the two sulfur atoms are adjacent, are very rare. The first stable 1,2-dithietane to be reported was the dithiatopazine, formed by intramolecular photodimerization of a bis(thionolactone): Heating dithiatopazine generates eliminates the sulfur atoms as unstable disulfur, and other dithietanes are presumed to decompose similarly. A stable 1,2-dithietane derivative is trans-3,4-diethyl-1,2-dithietane 1,1-dioxide: That compound is formed by the spontaneous dimerization of syn-propanethial-S-oxide, the lachrymatory agent found in onions. Another derivative class of 1,2-dithietanes are the 1,2-dithietes, containing two adjacent sulfur atoms and two trigonal planar carbon centers. == 1,3-Dithietanes ==

In 1,3-dithietanes, the sulfur atoms are non-adjacent. The functional group is used industrially in various biocides. Examples include the antibiotic Cefotetan and the pesticide Fosthietan. 1,3-Dithietane itself, a colorless, easily sublimed, crystalline, unpleasant-smelling solid with melting point 105-106 °C, was first prepared in 1976 by reaction of bis(chloromethyl) sulfoxide with sodium sulfide followed by THF-borane reduction of the first formed 1,3-dithietane 1-oxide: Carbon-substituted 1,3-dithietanes are well known, with the first examples being described as early as 1872. Examples include 2,2,4,4-tetrachloro-1,3-dithietane, the photochemically-formed dimer of thiophosgene, and tetrakis(trifluoromethyl)-1,3-dithietane, [(CF3)2CS]2. Symmetric 1,3dithietanes are preferably synthesized from thiocarbonyl dimerization. Heating or irradiating dithietanes results in "dedimerization" to give the corresponding thiocarbonyl compounds. Oxidized forms of 1,3-dithietane are well known, although they are often not prepared from the dithietane. Examples include the so-called zwiebelanes (2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane S-oxides) from onion volatiles and 1,3-dithietane 1,1,3,3-tetraoxide, the so-called sulfene dimer: dimer, 2,2,4,4-tetrachloro-1,3-dithietane; center: a zwiebelane, found in onion volatiles; right: sulfene dimer They are more acidic than acyclic disulfones, but even so are hard to alkylate. In the desaurins, each carbon atom is attached to alkylidene substituents (i.e., a double bond). ==References==