Octasulfur is an
inorganic
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemist ...
substance with the chemical formula . It is an odourless and tasteless yellow solid, and is a major industrial chemical. It is the most common
allotrope
Allotropy or allotropism () is the property of some chemical elements to exist in two or more different forms, in the same physical State of matter, state, known as allotropes of the elements. Allotropes are different structural modifications o ...
of
sulfur
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...
and occurs widely in nature.
[Steudel, R., "Homocyclic Sulfur Molecules", Topics Curr. Chem. 1982, 102, 149.]
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
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
In chemistry, the standard state of a material (pure substance, mixture or solution) is a reference point used to calculate its properties under different conditions. A superscript circle ° (degree symbol) or a Plimsoll (⦵) character is use ...
. 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
Octasulfur is not typically produced as 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
The Claus process is the most significant gas desulfurizing process, recovering elemental sulfur from gaseous hydrogen sulfide. First patented in 1883 by the chemist Carl Friedrich Claus, the Claus process has become the industry standard.
Th ...
, associated with petroleum refineries.
See also
*
Sulfur (pharmacy)
References
External links
*
{{Periodic table (navbox)
Agricultural chemicals
Biology and pharmacology of chemical elements
Dietary minerals
Native element minerals
Eight-membered rings
Allotropes of sulfur