Octasulfur

Octasulfur is an inorganic substance with the chemical formula S₈. It is an odourless and tasteless yellow solid, and is a major industrial chemical. It is the most common allotrope of sulfur and occurs widely in nature.^[4]

Octasulfur

Stereo, skeletal formula of octathiocane Spacefill model of octathiocane
Names
Systematic IUPAC name cyclo-Octasulfur[1] Octathiocane[2] Cyclooctasulfane
Other names Octasulfur
Identifiers
CAS Number	10544-50-0 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:29385
ChEMBL	ChEMBL1235452 Y
ChemSpider	59726 Y
Gmelin Reference	2973
MeSH	Cyclooctasulfur
PubChem CID	66348
UNII	70FD1KFU70 Y
CompTox Dashboard (EPA)	DTXSID80872924
InChI InChI=1S/S8/c1-2-4-6-8-7-5-3-1 Y Key: JLQNHALFVCURHW-UHFFFAOYSA-N Y
SMILES S1SSSSSSS1
Properties
Chemical formula	S8
Molar mass	256.48 g·mol−1
Appearance	Vivid, yellow, translucent crystals
Density	2.07 g/cm3
Melting point	119 °C; 246 °F; 392 K
Boiling point	444.6 °C; 832.4 °F; 717.8 K
log P	6.117
Thermochemistry
Std molar entropy (S⦵298)	32 J·mol−1·K−1[3]
Std enthalpy of formation (ΔfH⦵298)	0 kJ/mol[3]
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

Nomenclature

The name octasulfur is the most commonly used for this chemical. It is systematically named cyclo-octasulfur (which is the preferred IUPAC name) and cyclooctasulfane. It is also the final member of the thiocane heterocylic series, where every carbon atom is substituted with a sulfur atom, thus this sulfur allotrope is systematically named octathiocane as well.

Structure

Main article: Allotropes of sulfur

The chemical consists of rings of 8 sulfur atoms. It 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 which only two are stable at standard conditions. The rhombohedral crystal form is the accepted standard state. The remaining polymorph is only stable between 96 and 115 °C at 100 kPa. Octasulfur forms several allotropes: α-sulfur, β-sulfur, γ-sulfur, and 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, which are typically yellow and are somewhat translucent.

Production and reactions

Main article: Sulfur

Octasulfur is not typically 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. International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSC–IUPAC. ISBN 0-85404-438-8. p. 49. Electronic version.
2. "cyclooctasulfur (CHEBI:29385)". Chemical Entities of Biological Interest. UK: European Bioinformatics Institute. Main.
3. Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 978-0-618-94690-7.
4. Steudel, R., "Homocyclic Sulfur Molecules", Topics Curr. Chem. 1982, 102, 149.

External links

• Media related to Octasulfur at Wikimedia Commons