Potassium pentasulfide

dipotassium pentasulfide

Names
Other names dipotassium sulphide, potassium polysulfide
Identifiers
CAS Number	12136-50-4
Properties
Chemical formula	K2S5
Appearance	red-orange prisms
Structure
Crystal structure	orthorhombic
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Potassium pentasulfide is the inorganic compound with the formula K₂S₅. It is a red-orange solid that dissolves in water. The salt decomposes rapidly in air. It is one of several polysulfide salts with the general formula M₂S_n, where M = Li, Na, K and n = 2, 3, 4, 5.^[1] The polysulfide salts of potassium and sodium are similar.

Preparation and reactions

The salt is prepared by the addition of elemental sulfur to potassium sulfide. An idealized equation is shown for potassium hydrosulfide:

2 KHS + 1/2 S₈ → K₂S₅ + H₂S

The structure consists of zigzag chains of S₅^2- linked to K⁺ ions.^[2]

Occurrence

Various polysulfides K₂S₂ - K₂S₆ are components of liver of sulfur. Polysulfides, like sulfides, can induce stress corrosion cracking in carbon steel and stainless steel.

References

1. F. Fehér" Potassium Disulfide", "Potassium Tetrasulfide" "Potassium Pentasulfide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 361-367.
2. Barbara Kelly and Peter Woodward (1976). "Crystal structure of dipotassium pentasulphide". Journal of the Chemical Society, Dalton Trans.: 1314–1316. doi:10.1039/DT9760001314.