Detection of Reactive Sulfur Molecules (S6, S7, S9, S∞) in Commercial Sulfur, in Sulfur Minerals, and in Sulfur Melts Slowly Cooled to 20 °C [1].

Quantitative analysis by high-pressure liquid chromatography shows that all commercial samples of elemental sulfur besides S8 contain traces of S7 (up to 0.56%) and in some cases also S6, S9 , and polymeric sulfur (S∞). Pure S8 can be obtained by recrystallization from CS2 . Elemental sulfur minerals also quite often contain traces of S7 (up to 0.3%). Since neither irradiation by daylight at 20 °C nor heating to 90 °C for 41 days did convert α-S8 into S7 , the reactive sulfur molecules Sn (n≠8) are believed to origin from liquid or gaseous sulfur which are known to be complex equilibrium mixtures of many Sn species. Sulfur melts slowly cooled (within 0.6 to 145 h) from 122 to 20 °C in fact contain S7 (minimum 0.2%) and at cooling rates of <24 h also other non-S8 molecules. Solid solutions of S7 in α-S8 have also been prepared by cocrystallization of the compounds from CS2. In contrast to pure α-S8, these solid solutions are pale-yellow at 77 K, and the implications of these findings for the surface composition of Jupiter’s satellite Io and for the mechanical properties of “formed sulfur” (Prills, Rotoform, Slates, etc.) are discussed.