Dimethyl tetrasulfide, thermal

The mechanisms (a)-(c) can also be discussed in connection with the thermal decomposition and rearrangement reactions of organic polysulfides. For example, dimethyl tetrasulfide when heated to 80 °G for several hours disproportionates to the corresponding tri-, penta- and hexasulfides. On prolonged heating small amounts of disulfide are formed in addition... 

The abstraction of the internally linked sulfur from the higher polysulfides by copper is the basis of the "active" sulfur determination. It is usually postulated as a heterogeneous reaction at the surface of the metal however Kende, Pickering and Tobolsky [19] showed that homogeneous thermal decomposition of dimethyl tetrasulfide occurred at temperatures as low as 325 K (52 C). Trivette and Coran [23] studied the exchange reaction... 

The thermal decomposition of dimethyl trisulfide at 80 °C also results in the formation of di- and tetrasulfides . It was further established that the decomposition proceeds via a radical mechanism, probably homolytic S-S cleavage, since in a weakly polar medium such as benzoyl peroxide and triethylamine, the rate of decomposition is greatly accelerated. 

In general, the thermal stability of polysulfides decreases as the length of the polysulfide linkage increases. The bond dissociation energies of dimethyl di-, tri-and tetrasulfides follow the same trend, being 69, 46 and 37 kcaLmole", respectively this has been rationalized in terms of resonance interaction of the free electron with the sulfur chain... 

Recently, sulfur transfer to dienes using 6,6-dimethyl-1,4-diseleno-3,7-tetrasulfide and other diselenotetrasulfides was reinvestigated. It is not even necessary to use diselenotetrasulfides as actual reagents. Indeed, they form in the reaction medium from the corresponding diselenides with an excess of elemental sulfur (eq 4). Under the thermal conditions required for efficient sulfur transfers, a homolytic cleavage of the Se-S bond results in generation of active sulfur species delivering sulfur to dienes. 

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