Thermal Polymerization and Depolymerization Reactions of 10 Sulfur Allotropes Studied by HPLC and DSC [1]

Abstract

Abstract The thermal decomposition (polymerization, depolymerization, ring interconversion) of a number of sulfur allotropes (S 6 , S 7 , S 8 , S 10 , S 12 , S 13 , S 20 , polymeric sulfur) has been investigated theoretically (on the basis of Gee's theory) and experimentally by differential scanning calorimetry (DSC) and high‐pressure liquid chromatography (HPLC) in the temperature region of 30–250°C. While the polymerization of liquid S 8 is endothermic and endentropic (ΔS > 0), liquid S 7 polymerizes exothermically and endentropically, and liquid S 6 exothermically but exentropically (ΔS > 0). Therefore, a floor temperature exists for the polymerization of S 8 and a hypothetical very high ceiling temperature for the polymerization of S 6 , while S 7 is unstable with respect to polymerization over the whole temperature region. Excepting S 8 , all investigated cyclic sulfur allotropes yield polymeric sulfur on heating to 60–150°C followed by depolymerization to the equilibrium sulfur melt consisting mainly of S 8 , some S 7 , and traces of S 6 , S 9 , S 12 and other rings. Polymeric sulfur (S μ ) slowly dissolves in CS 2 at 20°C to give S 8 , S 7 and traces of other rings (mainly S 6 , S 9 , S 12 ). On heating of the S μ /CS 2 mixture in sealed ampoules to 80–100°C complete dissolution takes place within several hours or days and the rings S 8 and S 7 are the main products.