The completely unexpected and unpredictable experimental fact of the formation of diatomic gaseous sulfur in the reaction of low-temperature catalytic decomposition of hydrogen sulfide made us very carefully and comprehensively analyze the very extensive experimental material on the study of the properties of elemental sulfur in all three aggregate states. As a result, a review was prepared with the same name, which was submitted for publication to the Russian Journal of General Chemistry, Vestnik of the Russian Academy of Sciences, the Russian Journal of Structural Chemistry, but publication refusals were received. Finally, the English version of the review was submitted to a specialized Journal of Sulfur Chemistry where it was published JSulfChem-2019-40-4-435-450-Startsev .
It was shown that the diatomic gaseous sulfur obtained by us for the first time is in the ground triplet state, as is its isoelectronic analog, oxygen. In the thermal processes of the dissociation of elemental sulfur and decomposition of hydrogen sulfide, diatomic sulfur is formed in a metastable singlet state, the thermodynamic parameters of which are given in the handbooks. Therefore, based on the analogy with molecular oxygen, we have to conclude that the standard enthalpy of formation of triplet sulfur should also be equal to zero
ΔfHо298 (S2 X 3S–g ) = 0.
The gaseous diatomic sulfur S2 is stable at temperatures up to 200 ° C and higher, has a sharp nauseating smell, crystallizes at the temperature of liquid nitrogen in the form of delicate white snowflakes, and sublimates after heating to room temperature. It is well dissolved in water (over 5 g / liter). The aqueous sulfur solution is colorless, has a neutral pH like that of the original water, has no absorption bands in the IR and Raman spectra, and the refractive index corresponds to the refractive index of water. This is characteristic of many dissolved diatomic gases that do not interact with water.
From saturated aqueous solutions of diatomic sulfur, a previously unknown white globular modification of solid sulfur was obtained. The size of white globules of almost regular spherical shape reaches 5 – 10 microns, while the smallest particles are transparent and colorless. Electron diffraction on an individual sulfur globule indicates its hexagonal structure with interplanar spacings of 0.45, 0.29 and 0.15 nm.
When dissolved in polar solvents or when adsorbed onto carriers, the colorless triplet sulfur acquires a yellow color, while maintaining a diatomic state.
