Octasulfur

Octasulfur

Names
Systematic IUPAC name Octathiocane[1]
Identifiers
CAS Number	10544-50-0
ChEBI	CHEBI:29385
ChEMBL	ChEMBL1235452
ChemSpider	59726
Gmelin Reference	2973
Jmol 3D model	Interactive image
MeSH	Cyclooctasulfur
PubChem	66348
InChI InChI=1S/S8/c1-2-4-6-8-7-5-3-1 Key: JLQNHALFVCURHW-UHFFFAOYSA-N
SMILES S1SSSSSSS1
Properties
Chemical formula	S8
Molar mass	256.48 g·mol^−1
Appearance	Vivid, yellow, translucent crystals
Density	2.07 g cm^−3
Melting point	119 °C; 246 °F; 392 K
Boiling point	159 °C; 318 °F; 432 K (decomposes)
log P	6.117
Thermochemistry
Std molar entropy (S^o298)	32 J·mol^−1·K^−1[2]
Std enthalpy of formation (ΔfH^o298)	0 kJ·mol^−1[2]
Related compounds
Related compounds	Hexathiane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Octasulfur is an inorganic chemical with the chemical formula S
8. It is a yellow solid, and is odourless and tasteless. It is the most common allotrope of sulfur. It is a major industrial chemical that occurs widely in nature.^[3]

Nomenclature

The name octasulfur is the most commonly used; the preferred IUPAC name is cyclo-octasulfur. The compound is systematically named octathiocane, and cyclo-octasulfur. It is also the final member of the thiocane heterocylic series, where every carbon is substituted with a sulfur atom.

Structure

The compound adopts a crown conformation with D_4d point group symmetry. The S-S bond lengths are equal, at about 2.05 Å. Octasulfur crystallizes in three distinct polymorphs: rhombohedral, and two monoclinic forms, of these only two are stable at standard conditions. The rhombohedral crystal form is the accepted standard. The remaining polymorph is only stable between 96 and 115 °C at 100 kPa. Octasulfur forms several allotropes: α-Sulfur, β-sulfur, γ-sulfur, λ-sulfur.

λ-Sulfur is the liquid form of octasulfur, from which γ-sulfur can be crystallised by quenching. If λ-sulfur is crystallised slowly, it will revert to β-sulfur. Since it must have been heated over 115 °C, neither crystallised β-sulfur, or γ-sulfur will be pure. The only known method of obtaining pure γ-sulfur, is by crystallising from solution.

Octasulfur easily forms large crystals, these crystals are typically yellow and are somewhat translucent.

Production and reactions

It is typically not produced as S₈ per se. It is the main (99%) component of elemental sulfur, which is recovered from volcanic sources and is a major product of the Claus Process, associated with petroleum refineries.

See also

• Sulfur (pharmacy)

References

1. "cyclooctasulfur (CHEBI:29385)". Chemical Entities of Biological Interest. UK: European Bioinformatics Institute. Main.
2. Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 0-618-94690-X.
3. Steudel, R., "Homocyclic Sulfur Molecules", Topics Curr. Chem. 1982, 102, 149.