Sodium polysulfide
 Sodium pentasulfide, a representative component of sodium polysulfide
| |
| |
| Names | |
|---|---|
| Other names
Sodium sulfane; Viradon
| |
| Identifiers | |
| |
3D model (JSmol)
|
|
| ChemSpider |
|
| ECHA InfoCard | 100.014.261 |
| EC Number |
|
PubChem CID
|
|
| UN number | UN3266 |
CompTox Dashboard (EPA)
|
|
| |
| Properties | |
| Na2Sx | |
| Hazards | |
| GHS labelling: | |
   
| |
| Danger | |
| H228, H301, H311, H314, H400 | |
| P210, P240, P241, P260, P264, P270, P273, P280, P301+P310, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P312, P321, P322, P330, P361, P363, P370+P378, P391, P405, P501 | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-combustible |
| Safety data sheet (SDS) | AGFA |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Sodium polysulfide is a general term for salts with the formula Na2Sx, where x = 2 to 5. The species Sx2−, called polysulfide anions, include disulfide (S22−), trisulfide (S32−), tetrasulfide (S42−), and pentasulfide (S52−). In principle, but not in practice, the chain lengths could be longer.[1][2] The salts are dark red solids that dissolve in water to give highly alkaline and corrosive solutions. In air, these salts oxidize, and they evolve hydrogen sulfide by hydrolysis.
Structure
[edit]The polysulfide anions form chains with S---S bond distances around 2 Å in length. The chains adopt skewed conformations. In the solid state, these salts are dense solids with strong association of the sodium cations with the anionic termini of the chains.[3]
Production and occurrence
[edit]Sodium polysulfide can be produced by dissolving sulfur in a solution of sodium sulfide.[4] Alternatively they are produced by the redox reaction of aqueous sodium hydroxide with sulfur at elevated temperatures.[5] Finally they arise by the reduction of elemental sulfur with sodium, a reaction often conducted in anhydrous ammonia.
These salts are used in the production of polysulfide polymers, as a chemical fungicide, as a blackening agent on copper jewellery, as a component in a polysulfide bromide battery, as a toner in a photochemical solution, and in the tanning industry to remove hair from hides.
Reactions
[edit]As exploited in the sodium-sulfur battery, the polysulfides absorb and release reducing equivalents by breaking and making S-S bonds, respectively. An idealized reaction for sodium tetrasulfide is shown:
- Na2S4 + 2 Na ⇌ 2 Na2S2
Alkylation gives organic polysulfides according to the following idealized equation:
- Na2S4 + 2 RX → 2 NaX + R2S4
Alkylation with an organic dihalide gives polymers called thiokols.
Protonation of these salts gives hydrogen sulfide and elemental sulfur, as illustrated by the reaction of sodium pentasulfide:
- Na2S5 + 2 HCl → H2S + 4 S + 2 NaCl
References
[edit]- ^ Steudel, Ralf (2003-10-23). Elemental Sulfur and Sulfur-Rich Compounds I. Berlin Heidelberg: Springer Science & Business Media. ISBN 978-3-540-40191-9.
- ^ Steudel, Ralf (2003-11-17). Elemental Sulfur and Sulfur-Rich Compounds II. Berlin Heidelberg: Springer Science & Business Media. ISBN 978-3-540-40378-4.
- ^ Rosén, E.; Tegman, R. (1988). "Preparative and X - ray powder diffraction study of the polysulfides Na2S2, Na2S4 and Na2S5". Acta Chemica Scandinavica. 25: 3329–3336. doi:10.3891/acta.chem.scand.25-3329.
- ^ F. Fehér" Sodium Disulfide", "Sodium Tetrasulfide" "Sodium Pentasulfide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 361-367.
- ^ Lee, T.C.P. (1999). Properties and applications of elastomeric polysulfides. Rapra Technology. p. 4. ISBN 978-1859571583.