Polysulfane
A polysulfane is a chemical compound of formula H2Sn, where n > 1 (although disulfane (H2S2) 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] H2S2 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 −(S)n−, e.g. organic polysulfanes R1−(S)n−R2.
Structures
Polysulfanes consist of unbranched chains of sulfur atoms
Reactions and properties
Polysulfanes can easily be
- 8 H2Sn → 8 H2S + (n − 1) S8 (in this chemical reaction, S8 is cyclo-octasulfur, one of the allotropes of sulfur)
This
In contrast to the
- S2− + (n − 1) S → [Sn]2−
Beyond H2S and H2S2, many higher polysulfanes H2Sn (n = 3 – 8) are known.[7] They have unbranched sulfur chains. Starting with disulfane H2S2, 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
|
---|---|---|---|---|
H2S | Sulfane | 1.363 g/dm3 (gas) | 1740 ( kPa , 21 °C) (gas)
|
−60 °C (−76 °F) |
H2S2
|
Disulfane | 1.334 | 87.7 mmHg (11,690 Pa) | 70 °C (158 °F) |
H2S3 | Trisulfane | 1.491 | 1.4 mmHg (190 Pa) | 170 °C (338 °F) |
H2S4 | Tetrasulfane | 1.582 | 0.035 mmHg (4.7 Pa) | 240 °C (464 °F) |
H2S5 | Pentasulfane | 1.644 | 0.0012 mmHg (0.16 Pa) | 285 °C (545 °F) |
H2S6 | Hexasulfane | 1.688 | ? | ? |
H2S7 | Heptasulfane | 1.721 | ? | ? |
H2S8 | 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:
- Na2Sn + 2 HCl → 2 NaCl + H2Sn (n = 4, 5, 6)
- SnCl2 + 2 H2Sm → 2 HCl + H2Sn+2m
The reaction of polysulfanes with sulfur dichloride or disulfur dichloride produces long-chain dichloropolysulfanes:
- 2 SCl2 + H2Sn → 2 HCl + S2+nCl2
- 2 S2Cl2 + H2Sn → 2 HCl + S4+nCl2
The reaction with a sulfite salt (a base) quantitatively decomposes the polysulfane to produce thiosulfate and hydrogen sulfide:
- (n − 1) SO2−3 + H2Sn → (n − 1) S2O2−3 + H2S
References
- )
- OCLC 48138330.
- ^ doi:10.1007/b13182
- .
- ^ a b c Greenwood and Earnshaw, p. 683
- doi:10.1007/b13182