3D model (JSmol)
|E number||E536 (acidity regulators, ...)|
|Molar mass||368.35 g/mol (anhydrous)|
422.388 g/mol (trihydrate)
|Appearance||Light yellow, crystalline granules|
|Density||1.85 g/cm3 (trihydrate)|
28.9 g/100 mL (20 °C)
|Solubility||insoluble in ethanol, ether|
|R-phrases (outdated)||R32, R52, R53|
|S-phrases (outdated)||S50(B), S61|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|6400 mg/kg (oral, rat)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Potassium ferrocyanide is produced industrially from hydrogen cyanide, ferrous chloride, and calcium hydroxide, the combination of which affords Ca2[Fe(CN)6]·11H2O. This solution is then treated with potassium salts to precipitate the mixed calcium-potassium salt CaK2[Fe(CN)6], which in turn is treated with potassium carbonate to give the tetrapotassium salt.
Historically, the compound was manufactured from organic compounds containing nitrogen, iron filings, and potassium carbonate. Common nitrogen and carbon sources were torrified horn, leather scrap, offal, or dried blood.
Treatment of potassium ferrocyanide with nitric acid gives H2[Fe(NO)(CN)5]. After neutralization of this intermediate with sodium carbonate, red crystals of sodium nitroprusside can be selectively crystallized.
- 2 K4[Fe(CN)6] + Cl2 → 2 K3[Fe(CN)6] + 2 KCl
This reaction can be used to remove potassium ferrocyanide from a solution.
Potassium ferrocyanide finds many niche applications in industry. It and the related sodium salt are widely used as anticaking agents for both road salt and table salt. The potassium and sodium ferrocyanides are also used in the purification of tin and the separation of copper from molybdenum ores. Potassium ferrocyanide is used in the production of wine and citric acid.
In the EU, ferrocyanides (E 535–538) were, as of 2018, solely authorised in two food categories as salt substitutes. Kidneys are the organ for ferrocyanide toxicity.
It can also be used in animal feed.
In the laboratory, potassium ferrocyanide is used to determine the concentration of potassium permanganate, a compound often used in titrations based on redox reactions. Potassium ferrocyanide is used in a mixture with potassium ferricyanide and phosphate buffered solution to provide a buffer for beta-galactosidase, which is used to cleave X-Gal, giving a bright blue visualization where an antibody (or other molecule), conjugated to Beta-gal, has bonded to its target. On reacting with Fe(3) it gives a Prussian blue colour. Thus it is used as an identifying reagent for iron in labs.
Potassium ferrocyanide can be used as a fertilizer for plants.
Prior to 1900 AD, before the invention of the Castner process, potassium ferrocyanide was the most important source of alkali metal cyanides. In this historical process, potassium cyanide was produced by decomposing potassium ferrocyanide:
K4[Fe(CN)6] → 4 KCN + FeC2 + N2
Like other metal cyanides, solid potassium ferrocyanide, both as the hydrate and anhydrous salts, has a complicated polymeric structure. The polymer consists of octahedral [Fe(CN)6]4− centers crosslinked with K+ ions that are bound to the CN ligands. The K+---NC linkages break when the solid is dissolved in water.
- "POTASSIUM FERROCYANIDE MSDS Number: P5763 - Effective Date: 12/08/96". J. T. Baker Inc. Retrieved 2012-04-08.
- Gail, E.; Gos, S.; Kulzer, R.; Lorösch, J.; Rubo, A.; Sauer, M.; Kellens, R.; Reddy, J.; Steier, N.; Hasenpusch, W. (October 2011). "Cyano Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a08_159.pub3.
- Von Wagner, Rudolf (1897). Manual of chemical technology. New York: D. Appleton & Co. p. 474 & 477.
- Seel, F. (1965). "Sodium Nitrosyl Cyanoferrate". In Brauer, G. (ed.). Handbook of Preparative Inorganic Chemistry. 2 (2nd ed.). New York: Academic Press. p. 1768. LCCN 63-14307.
- Peter Aggett, Fernando Aguilar, Riccardo Crebelli, Birgit Dusemund, Metka Filipič, Maria Jose Frutos, Pierre Galtier, David Gott, Ursula Gundert‐Remy, Gunter Georg Kuhnle, Claude Lambré, Jean‐Charles Leblanc, Inger Therese Lillegaard, Peter Moldeus, Alicja Mortensen, Agneta Oskarsson, Ivan Stankovic, Ine Waalkens‐Berendsen, Rudolf Antonius Woutersen, Matthew Wright and Maged Younes. (2018). "Re‐evaluation of sodium ferrocyanide (E 535), potassium ferrocyanide (E 536) and calcium ferrocyanide (E 538) as food additives". EFSA Journal. 16 (7): 5374. doi:10.2903/j.efsa.2018.5374.CS1 maint: multiple names: authors list (link)
- "EuSalt Expert Meeting on E 535 and E 536 as Feed Additives". EUSalt.
- Willans, M.J.; Wasylishen, R.E.; McDonald, R. "Polymorphism of potassium ferrocyanide trihydrate as studied by solid-state multinuclear NMR spectroscopy and X-ray diffraction" Inorganic Chemistry 2009, volume 48, p4342-4353
- "Cyanide (inorganic) compounds fact sheet". National Pollutant Inventory Australia.