Sodium polysulfide

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Sodium polysulfide
Na2S5 as chemdraw.png
Sodium pentasulfide, a representative component of sodium polysulfide
Na2S5Packing.tif
Names
Other names
Sodium sulfane; Viradon
Identifiers
1344-08-7
UN number UN3266
Properties
Na2Sx
Hazards
Safety data sheet AGFA
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-combustible
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

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] 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.[2]

S42- from the crystal structure, highlighting its skewed conformation.
S52- from the crystal structure, highlighting its skewed conformation.

Production and occurrence[edit]

Sodium polysulfide can produced by dissolving sulfur in a solution of sodium sulfide.[3] Alternatively they are produced by the redox reaction of aqueous sodium hydroxide with sulfur at elevated temperatures.[4] 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 H+ → H2S + 1/2 S8

References[edit]

  1. ^ Elemental Sulfur and Sulfur-Rich Compounds volumes I and II, Steudel, R., Ed.; Springer-Verlag: Berlin, 2003.
  2. ^ Rosén, E.; Tegman, R. "Preparative and X - ray powder diffraction study of the polysulfides Na2S2, Na2S4 and Na2S5" Acta Chemica Scandinavica 1988, volume 25, pp 3329-3336. doi:10.3891/acta.chem.scand.25-3329
  3. ^ 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.
  4. ^ Lee, T.C.P. (1999). Properties and applications of elastomeric polysulfides. Rapra Technology. p. 4. ISBN 978-1859571583.