Dimeric dithiocarbonate

The first stable a-dithione, 4,4 -bis(dimethylamino)dithiobenzil, has been synthesized by photolysis of the vinylene dithiocarbonate (55 Ar = p-Me2NCeH4). The dark red, crystalline product was found to have the structure (56) in the solid state, whereas it exists in solution as an equilibrium mixture of the valence tautomers (56) and (57). The equilibrium concentration of the dithiet form (57) was found to depend on the solvent, the temperature, and on the presence or absence of light. A kinetic study showed that the tautomerization process cleanly follows reversible first-order kinetics, i.e. a reversible formation of any dimer can be excluded. The enthalpy and entropy changes for the process (57) -> (56) were determined... 

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