Potassium pyrosulfate

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Potassium pyrosulfate (potassium disulfate) is a chemical compound, K₂S₂O₇ with CAS number of 7790-62-7. It contains the pyrosulfate anion S₂O₇²⁻ which has a dichromate like structure and can be visualised as two corner sharing SO₄ tetrahedra, with a bridging oxygen atom. ["The crystal structure determination and refinements of K₂S₂O₇, KNaS₂O₇ and Na₂S₂O₇ from X-ray powder and single crystal diffraction data" Ståhl K , Balic-Zunic T, da Silva F, Eriksen K M , Berg R W Fehrmann R Journal of Solid State Chemistry 178, 1697-1704, (2005) doi|10.1016/j.jssc.2005.03.022 ] A semi-structural formula for pyrosulfate ion is O₃SOSO₃²⁻. In this compound sulfur has an oxidation state of +6.

Potassium pyrosulfate is most commonly found as a preservative in consumer foods. The European Union approved food additive E-code for potassium disulfate is E224. As a food additive or preservative K₂S₂O₇ is also known as Potassium metabisulphite. [E-numbers database, Wageningen University food safety information -site, Food Technology Department http://www.food-info.net/uk/e/e224.htm]

Potassium pyrosulfate is used in analytical chemistry; samples are fused with potassium pyrosulfate,(or a mixture of potassium pyrosulfate and potassium fluoride, KF) to ensure complete dissolution prior to a quantitative analysis. ["Determination of quartz (free silica) in refractory clays" Trostbl L.J., Wynne D.J. Journal of the American Ceramic Society 23 1 18, (1940) doi|10.1111/j.1151-2916.1940.tb14187.x] ["Determination of gross alpha, plutonium, neptunium, and/or uranium by gross alpha counting on barium sulphate" C. W. Sill Analytical Chemistry, (1980) 52, 1452]

It is also used as a catalyst in conjunction with vanadium(V) oxide, for example. ["Sulfur trioxide production" BurkhardtD.B. US patent no.3362786 issued Jan 1968,]

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