A polysulfane is a
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
of
formula , where ''n'' > 1 (although
disulfane () is sometimes excluded).
Polysulfanes consist of unbranched chains of sulfur atoms
terminated with hydrogen atoms. Compounds containing 2 – 8 concatenated sulfur atoms have been isolated, longer chain compounds have been detected, but only in solution. is colourless, higher members are yellow with the colour increasing with the sulfur content. Even a trace of
alkali will cause
chemical decomposition
Chemical decomposition, or chemical breakdown, is the process or effect of simplifying a single chemical entity (normal molecule, reaction intermediate, etc.) into two or more fragments. Chemical decomposition is usually regarded and defined as th ...
, and containers need to be treated with acid to remove any traces of alkali. In the chemical literature the term polysulfanes is sometimes used for compounds containing , e.g. organic polysulfanes .
Since sulfur is a
chalcogen
The chalcogens (ore forming) ( ) are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioac ...
, polysulfanes can be classed as
hydrogen chalcogenide Hydrogen chalcogenides (also chalcogen hydrides or hydrogen chalcides) are binary compounds of hydrogen with chalcogen atoms (elements of group 16: oxygen, sulfur, selenium, tellurium, and polonium). Water, the first chemical compound in this serie ...
s.
Chemistry and properties
Polysulfanes are thermodynamically unstable with respect to decomposition (disproportionation) to and sulfur:
:
where is
''cyclo''-octasulfur or cyclooctasulfane, one of the allotropes of sulfur. However, the production of
polysulfide
Polysulfides are a class of chemical compounds containing chains of sulfur atoms. There are two main classes of polysulfides: inorganic and organic. Among the inorganic polysulfides, there are ones which contain anions, which have the general formu ...
ions from and S is thermodynamically favourable:
:; ΔH = −ve
Attempting to make a polysulfane by acidifying an alkali metal polysulfide salt (e.g.
sodium disulfide) simply produces
hydrogen sulfide, , and sulfur. Polysulfanes can be made from polysulfides by pouring polysulfide into cooled concentrated hydrochloric acid to produce a mixture of metastable polysulfanes as a yellow oil, from which individual compounds may be separated by fractional distillation. Other more selective syntheses are:
: (''n'' = 4, 5, 6)
:
The reaction of polysulfanes with
sulfur dichloride or
disulfur dichloride produces long-chain dichloropolysulfanes:
:
:
The reaction with a
sulfite salt (a base) quantitatively decomposes the polysulfane to produce
thiosulfate and hydrogen sulfide:
:
References
{{Hydrides by group
Hydrogen compounds
*