Octasulfur

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.[4]

Octasulfur
Stereo, skeletal formula of octathiocane
Spacefill model of octathiocane
Names
Systematic IUPAC name
cyclo-Octasulfur[1]
Octathiocane[2]
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
2973
MeSH Cyclooctasulfur
UNII
Properties
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 444.6 °C; 832.4 °F; 717.8 K
log P 6.117
Thermochemistry
32 J·mol−1·K−1[3]
Std enthalpy of
formation (ΔfH⦵298)
 0 kJ·mol−1[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; the preferred IUPAC name is cyclo-octasulfur. The substance 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
Main article: Allotropes of sulfur

The substance adopts a crown conformation with D4d 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. 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, 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

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 0-618-94690-X.
  4. Steudel, R., "Homocyclic Sulfur Molecules", Topics Curr. Chem. 1982, 102, 149.
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