Sodium polysulfide is a general term for salts with the formula Na₂ S_x, where ''x'' = 2 to 5. The species S_x²⁻, called

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 ...

anions, include

disulfide In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In ...

(S₂²⁻),

trisulfide In organic and organometallic chemistry, trisulfide is the functional group R-S-S-S-R. Examples include: * Diallyl trisulfide * Dimethyl trisulfide * Trisulfane (hydrogen trisulfide) Some inorganic compounds are also named trisulfides to reflec ...

(S₃²⁻), tetrasulfide (S₄²⁻), and pentasulfide (S₅²⁻). In principle, but not in practice, the chain lengths could be longer. The salts are dark red solids that dissolve in water to give highly

alkaline In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...

and

corrosive A corrosive substance is one that will damage or destroy other substances with which it comes into contact by means of a chemical reaction. Etymology The word ''corrosive'' is derived from the Latin verb ''corrodere'', which means ''to gnaw'', ...

solutions. In air, these salts oxidize, and they evolve hydrogen sulfide by

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

Structure

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.

Production and occurrence

Sodium polysulfide can be produced by dissolving sulfur in a solution of

sodium sulfide Sodium sulfide is a chemical compound with the formula Na2 S, or more commonly its hydrate Na2S·9 H2O. Both the anhydrous and the hydrated salts in pure crystalline form are colorless solids, although technical grades of sodium sulfide are gener ...

. Alternatively they are produced by the redox reaction of aqueous

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...

with sulfur at elevated temperatures. 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 polymer ''Thiokol'' is a trade mark for various organic polysulfide polymers. Thiokol polymers are used as an elastomer in seals and sealants. The distinction between the polymers first commercialized by the Thiokol Corporation and subsequent polysulfide ...

s, as a chemical

fungicide Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...

, as a blackening agent on

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

jewellery, as a component in a

polysulfide bromide battery The polysulfide-bromine battery (PSB; sometimes ''polysulphide-polybromide'' or "bromine-sulfur"), is a type of rechargeable electric battery, which stores electric energy in liquids, such as water-based solutions of two salts: sodium bromide and ...

, as a toner in a photochemical solution, and in the

tanning Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of artificial light in place of the sun **Sunless tanning, application of a stain or dye t ...

industry to remove hair from hides.

Reactions

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

thiokol Thiokol (variously Thiokol Chemical Corporation(/Company), Morton Thiokol Inc., Cordant Technologies Inc., Thiokol Propulsion, AIC Group, ATK Thiokol, ATK Launch Systems Group; finally Orbital ATK before becoming part of Northrop Grumman) was an ...

s. 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

{{sulfur compounds Polysulfides Sodium compounds