Polysulfane
Template:Short description A polysulfane is a chemical compound of formula Template:Chem2, where n > 1 (although disulfane (Template:Chem2) is sometimes excluded).[1][2][3] Compounds containing 2 – 8 sulfur atoms have been isolated, longer chain compounds have been detected, but only in solution.[4] Template:Chem2 is colourless, higher members are yellow with the colour increasing with the sulfur content. In the chemical literature the term polysulfanes is sometimes used for compounds containing Template:Chem2, e.g. organic polysulfanes Template:Chem2.
Structures
Polysulfanes consist of unbranched chains of sulfur atoms terminated with hydrogen atoms. The branched isomer of tetrasulfane Template:Chem2, in which the fourth sulfur is bonded to the central sulfur, would be described as trithiosulfurous acid, Template:Chem2. Computations suggests that it is less stable than the linear isomer Template:Chem2.[5] The S-S-S angles approach 90° in trisulfane Template:Chem2 and higher polysulfanes.[4]
Reactions and properties
Polysulfanes can easily be oxidised, and are thermodynamically unstable with respect to decomposition (disproportionation) readily to Template:Chem2 and sulfur:
- Template:Chem2 (in this chemical reaction, Template:Chem2 is cyclo-octasulfur, one of the allotropes of sulfur)
This decomposition reaction is catalyzed by alkali. To suppress this behavior, containers for polysulfanes are often pretreated with acid to remove traces of alkali.[6]
In contrast to the thermodynamic instability of polysulfates, polysulfide anions form spontaneously by treatment of Template:Chem2 with elemental sulfur:
Beyond Template:Chem2 and Template:Chem2, many higher polysulfanes Template:Chem2 (n = 3 – 8) are known.[7] They have unbranched sulfur chains. Starting with disulfane Template:Chem2, all known polysulfanes are liquids at room temperature. The density, boiling point and viscosity correlate with chain length. Physical properties of polysulfanes are given in the table below.[6]
| Chemical formula | Name | Density at 20 °C (g/cm3) | Vapour pressure | Extrapolated boiling point |
|---|---|---|---|---|
| [[Hydrogen sulfide|Template:Chem2]] | Sulfane | 1.363 g/dm3 (gas) | 1740 (kPa, 21 °C) (gas) | Template:Cvt |
| [[Disulfane|Template:Chem2]] | Disulfane | 1.334 | Template:Cvt | Template:Cvt |
| [[Trisulfane|Template:Chem2]] | Trisulfane | 1.491 | Template:Cvt | Template:Cvt |
| Template:Chem2 | Tetrasulfane | 1.582 | Template:Cvt | Template:Cvt |
| Template:Chem2 | Pentasulfane | 1.644 | Template:Cvt | Template:Cvt |
| Template:Chem2 | Hexasulfane | 1.688 | ? | ? |
| Template:Chem2 | Heptasulfane | 1.721 | ? | ? |
| Template:Chem2 | Octasulfane | 1.747 | ? | ? |
They also react with sulfite and cyanide producing thiosulfate and thiocyanate respectively.[6]
Polysulfanes can be made from polysulfides by pouring a solution of a polysulfide salt into cooled concentrated hydrochloric acid. A mixture of metastable polysulfanes separates as a yellow oil, from which individual compounds may be separated by fractional distillation. Other more selective syntheses are:
- Template:Chem2 (n = 4, 5, 6)
- Template:Chem2
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
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- ↑ IUPAC, Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (2006–) "polysulfanes". Script error: No such module "CS1 identifiers".Script error: No such module "TemplatePar".
- ↑ Script error: No such module "citation/CS1".
- ↑ Script error: No such module "citation/CS1".
- ↑ a b R. Steudel "Inorganic Polysulfanes H2Sn with n > 1" in Elemental Sulfur and Sulfur-Rich Compounds II (Topics in Current Chemistry) 2003, Volume 231, pp 99–125. Script error: No such module "CS1 identifiers".
- ↑ Script error: No such module "Citation/CS1".
- ↑ a b c Greenwood and Earnshaw, p. 683
- ↑ R. Steudel "Inorganic Polysulfanes H2S2 with n > 1" in Elemental Sulfur and Sulfur-Rich Compounds II (Topics in Current Chemistry) 2003, Volume 231, pp 99-125. Script error: No such module "CS1 identifiers".
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