Potassium ferrocyanide: Difference between revisions

Potassium hexacyanidoferrate(II)
Names
	IUPAC name Potassium hexacyanidoferrate(II)
	Other names (Yellow) Prussiate of Potash; Potassium hexacyanoferrate (II) trihydrate; Tetrapotassium ferrocyanide trihydrate; Ferrate hexacyano tetrapotassium trihydrate;
Identifiers
CAS Number	13943-58-3 (anhydrous) ; 14459-95-1 (trihydrate) ;
3D model (JSmol)	Interactive image;
ChemSpider	20162028;
ECHA InfoCard	100.034.279
EC Number	237-722-2;
E number	E536 (acidity regulators, ...)
PubChem CID	161067;
UNII	GTP1P30292 (anhydrous) ; 961WP42S65 (trihydrate) ;
CompTox Dashboard (EPA)	DTXSID60892423 ;
	InChI InChI=1S/6CN.Fe.4K.3H2O/c61-2;;;;;;;;/h;;;;;;;;;;;31H2/q6-1;+2;4+1;;; Key: UTYXJYFJPBYDKY-UHFFFAOYSA-N;
	SMILES [K+].[K+].N#C[Fe-4](C#N)(C#N)(C#N)(C#N)C#N.[K+].[K+];
Properties
Chemical formula	K4[Fe(CN)6]
Molar mass	368.35 g/mol (anhydrous); 422.388 g/mol (trihydrate)
Appearance	Light yellow, crystalline granules
Density	1.85 g/cm3 (trihydrate)
Boiling point	(decomposes)
Solubility in water	trihydrate ; 28.9 g/100 mL (20 °C)
Solubility	insoluble in ethanol, ether
Magnetic susceptibility (χ)	−130.0·10−6 cm3/mol
Hazards
	GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H411
NFPA 704 (fire diamond)	1 0 0
Flash point	Non-flammable
	Lethal dose or concentration (LD, LC):
LD50 (median dose)	6400 mg/kg (oral, rat)
Related compounds
Other anions	Potassium ferricyanide
Other cations	Sodium ferrocyanide; Prussian blue
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

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Potassium hexacyanidoferrate(II) is the inorganic compound with formula K₄[Fe(CN)₆]·3H₂O. It is the potassium salt of the coordination complex [Fe(CN)₆]⁴⁻. This salt forms lemon-yellow monoclinic crystals.

Synthesis

In 1752, the French chemist Pierre Joseph Macquer (1718–1784) first reported the preparation of Potassium hexacyanidoferrate(II), which he achieved by reacting Prussian blue (iron(III) ferrocyanide) with potassium hydroxide.^[4]^[5]

Modern production

Potassium hexacyanidoferrate(II) is produced industrially from hydrogen cyanide, iron(II) 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.^[6]

Historical production

Historically, the compound was manufactured from nitrogenous organic material, iron filings, and potassium carbonate.^[7] Common nitrogen and carbon sources were torrified horn, leather scrap, offal, or dried blood. It was also obtained commercially from gasworks spent oxide (purification of city gas from hydrogen cyanide).

Chemical reactions

Treatment of potassium hexacyanidoferrate(II) 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.^[8]

Upon treatment with chlorine gas, potassium hexacyanidoferrate(II) converts to potassium hexacyanidoferrate(III):

2 K₄[Fe(CN)₆] + Cl₂ → 2 K₃[Fe(CN)₆] + 2 KCl

This reaction can be used to remove potassium hexacyanidoferrate(II) from a solution.^{[citation needed]}

A famous reaction involves treatment with ferric salts, most commonly Iron(III) chloride, to give Prussian blue. In the reaction with Iron(III) chloride, producing Potassium chloride as a side-product:

3 K₄[Fe(CN)₆] + 4 FeCl₃ → Fe₄[Fe(CN)₆]₃ + 12 KCl

With the composition Fe^III
₄[Fe^II
(CN)
₆]
₃, this insoluble but deeply coloured material is the blue of blueprinting, as well as on many famous paintings such as The Great Wave off Kanagawa and The Starry Night.

Applications

Potassium hexacyanidoferrate(II) 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 hexacyanidoferrates(II) are also used in the purification of tin and the separation of copper from molybdenum ores. Potassium hexacyanidoferrate(II) is used in the production of wine and citric acid.^[6]

In the EU, hexacyanidoferrates(II) (E 535–538) were, as of 2017, solely authorised in two food categories as salt additives.

It can also be used in animal feed.^[9]

In the laboratory, potassium hexacyanidoferrate(II) is used to determine the concentration of potassium permanganate, a compound often used in titrations based on redox reactions. Potassium hexacyanidoferrate(II) 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 hexacyanidoferrate(II) can be used as a fertilizer for plants.^{[citation needed]}

Prior to 1900, before the invention of the Castner process, potassium hexacyanidoferrate(II) was the most important source of alkali metal cyanides.^[6] In this historical process, potassium cyanide was produced by decomposing potassium hexacyanidoferrate(II):^[7]

K₄[Fe(CN)₆] → 4 KCN + FeC₂ + N₂

Structure

Like other metal cyanides, solid potassium hexacyanidoferrate(II), 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.^[10] The K⁺---NC linkages break when the solid is dissolved in water.^{[clarification needed]}^{[citation needed]}

Toxicity

The toxicity in rats is low, with lethal dose (LD₅₀) at 6400 mg/kg.^[2]^{[better source needed]} The kidneys are the organ for ferrocyanide toxicity.^[11]

References

^ Five Hundred Useful and Amusing Experiments in Chemistry, and in the Arts and Manufactures: With Observations on the Properties Employed, and Their Application to Useful Purposes. Thomas Tegg. 1825.
^ ^a ^b "POTASSIUM FERROCYANIDE MSDS Number: P5763 - Effective Date: 12/08/96". J. T. Baker Inc. Archived from the original on 2015-11-21. Retrieved 2012-04-08.
^ https://chem.nlm.nih.gov/chemidplus/rn/13943-58-3 ^{[dead link‍]}
^ Macquer (1752). "Éxamen chymique de bleu de Prusse" [Chemical examination of Prussian blue]. Histoire de l'Académie Royale des Sciences …, § Mémoires de l'Académie royale des Sciences (in French): 60–77. From pp. 63-64: "Après avoir essayé ainsi inutilement de décomposer le bleu de Prusse par les acides, … n'avoit plus qu'une couleur jaune un peu rousse." (After having tried so vainly to decompose Prussian blue by acids, I made recourse to alkalies. I put a half ounce of this [Prussian] blue in a flask, and I poured on it ten ounces of a solution of nitre fixed by tartar [i.e., potassium nitrate (nitre) which is mixed with crude cream of tartar and then ignited, producing potassium carbonate]. As soon as these two substances had been mixed together, I saw with astonishment that, without the aid of heat, the blue color had entirely disappeared; the powder [i.e., precipitate] at the bottom of the flask had only a rather gray color: having put this vessel on a sand bath in order to heat the solution until it simmered, this gray color also disappeared entirely, and all that was contained in the flask, both the powder [i.e., precipitate] and the solution, had only a yellow color [that was] a little red.)
^ Munroe, Charles E.; Chatard, Thomas M. (1902). "Manufactures: Chemicals and Allied Products". Twelfth Census of the United States: Bulletins (210): 1–306.; see p. 31.
^ ^a ^b ^c 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. ISBN 978-3527306732.
^ ^a ^b 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. Vol. 2 (2nd ed.). New York: Academic Press. p. 1768. LCCN 63-14307. Archived from the original on 2010-03-07. Retrieved 2017-09-10.
^ "EuSalt Expert Meeting on E 535 and E 536 as Feed Additives". EUSalt. Archived from the original on 2019-05-12. Retrieved 2018-12-06.
^ Willans, Mathew J.; Wasylishen, Roderick E.; McDonald, Robert (2009-05-18). "Polymorphism of Potassium Ferrocyanide Trihydrate as Studied by Solid-State Multinuclear NMR Spectroscopy and X-ray Diffraction". Inorganic Chemistry. 48 (10): 4342–4353. doi:10.1021/ic802134j. ISSN 0020-1669. PMID 19425611.
^ 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. PMC 7009536. PMID 32626000.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Kosugi, Nobuhiro; Yokoyama, Toshihiko; Kuroda, Haruo (May 1986). "Polarization dependence of XANES of square-planar Ni(CN)2−4 ion. A comparison with octahedral Fe(CN)4−6 and Fe(CN)3−6 ions". Chemical Physics. 104 (3): 449–453. doi:10.1016/0301-0104(86)85034-0. ISSN 0301-0104.

External links

"Cyanide (inorganic) compounds fact sheet". National Pollutant Inventory Australia.
"Potassium Ferrocyanide in Salt Is Entirely Safe To Consume". rediff.com.^{[permanent dead link‍]}

[1] Five Hundred Useful and Amusing Experiments in Chemistry, and in the Arts and Manufactures: With Observations on the Properties Employed, and Their Application to Useful Purposes. Thomas Tegg. 1825.

[JTBaker-2] "POTASSIUM FERROCYANIDE MSDS Number: P5763 - Effective Date: 12/08/96". J. T. Baker Inc. Archived from the original on 2015-11-21. Retrieved 2012-04-08.

[3] ttps://chem.nlm.nih.gov/chemidplus/rn/13943-58-3 ^{[dead link‍]}

[4] Macquer (1752). "Éxamen chymique de bleu de Prusse" [Chemical examination of Prussian blue]. Histoire de l'Académie Royale des Sciences …, § Mémoires de l'Académie royale des Sciences (in French): 60–77. From pp. 63-64: "Après avoir essayé ainsi inutilement de décomposer le bleu de Prusse par les acides, … n'avoit plus qu'une couleur jaune un peu rousse." (After having tried so vainly to decompose Prussian blue by acids, I made recourse to alkalies. I put a half ounce of this [Prussian] blue in a flask, and I poured on it ten ounces of a solution of nitre fixed by tartar [i.e., potassium nitrate (nitre) which is mixed with crude cream of tartar and then ignited, producing potassium carbonate]. As soon as these two substances had been mixed together, I saw with astonishment that, without the aid of heat, the blue color had entirely disappeared; the powder [i.e., precipitate] at the bottom of the flask had only a rather gray color: having put this vessel on a sand bath in order to heat the solution until it simmered, this gray color also disappeared entirely, and all that was contained in the flask, both the powder [i.e., precipitate] and the solution, had only a yellow color [that was] a little red.)

[5] Munroe, Charles E.; Chatard, Thomas M. (1902). "Manufactures: Chemicals and Allied Products". Twelfth Census of the United States: Bulletins (210): 1–306.; see p. 31.

[Ullmann-6] 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. ISBN 978-3527306732.

[Wagner-7] Von Wagner, Rudolf (1897). Manual of chemical technology. New York: D. Appleton & Co. p. 474 & 477.

[8] Seel, F. (1965). "Sodium nitrosyl cyanoferrate". In Brauer, G. (ed.). Handbook of Preparative Inorganic Chemistry. Vol. 2 (2nd ed.). New York: Academic Press. p. 1768. LCCN 63-14307. Archived from the original on 2010-03-07. Retrieved 2017-09-10.

[9] "EuSalt Expert Meeting on E 535 and E 536 as Feed Additives". EUSalt. Archived from the original on 2019-05-12. Retrieved 2018-12-06.

[10] Willans, Mathew J.; Wasylishen, Roderick E.; McDonald, Robert (2009-05-18). "Polymorphism of Potassium Ferrocyanide Trihydrate as Studied by Solid-State Multinuclear NMR Spectroscopy and X-ray Diffraction". Inorganic Chemistry. 48 (10): 4342–4353. doi:10.1021/ic802134j. ISSN 0020-1669. PMID 19425611.

[11] 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. PMC 7009536. PMID 32626000.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[12] Kosugi, Nobuhiro; Yokoyama, Toshihiko; Kuroda, Haruo (May 1986). "Polarization dependence of XANES of square-planar Ni(CN)2−4 ion. A comparison with octahedral Fe(CN)4−6 and Fe(CN)3−6 ions". Chemical Physics. 104 (3): 449–453. doi:10.1016/0301-0104(86)85034-0. ISSN 0301-0104.

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@@ Line 1: / Line 1: @@
+{{Short description|Chemical compound}}
-[[Image:800px-Kaliumhexacyanoferrat II.jpg|200px|thumb|Small yellow crystals]]
+{{Distinguish|potassium ferricyanide}}
+{{chembox
+| Verifiedfields = changed
+| Watchedfields  = changed
+| verifiedrevid  = 444997361
+| Name           = Potassium hexacyanidoferrate(II)
+| ImageFile1     = Structure of potassium ferrocyanide.png
+| ImageFile2     = Potassium Ferrocyanide.png
+| ImageFile3     = Potassium hexacyanidoferrate(II).jpg
+| ImageSize3     = 150px
+| ImageName3     = Potassium ferrocyanide trihydrate
+| IUPACName      = Potassium hexacyanidoferrate(II)
+| OtherNames     = {{Unbulleted list
+ | (Yellow) Prussiate of Potash<ref>{{Cite book|url=https://play.google.com/books/reader?printsec=frontcover&output=reader&id=gXwPAAAAYAAJ&pg=GBS.PA8|title = Five Hundred Useful and Amusing Experiments in Chemistry, and in the Arts and Manufactures: With Observations on the Properties Employed, and Their Application to Useful Purposes|year = 1825|publisher = Thomas Tegg}}</ref>
+ | Potassium&nbsp;hexacyanoferrate&nbsp;(II) trihydrate
+ | Tetrapotassium&nbsp;ferrocyanide trihydrate
+ | Ferrate&nbsp;hexacyano tetrapotassium trihydrate<ref name=JTBaker/>
+ }}
+| Section1       = {{Chembox Identifiers
+| CASNo = 13943-58-3
+| CASNo_Ref = {{cascite|correct|CAS}}
+| CASNo_Comment = (anhydrous)
+| CASNo2_Ref = {{cascite|correct|CAS}}
+| CASNo2 = 14459-95-1
+| CASNo2_Comment = (trihydrate)
+| ChemSpiderID = 20162028
+| EINECS = 237-722-2
+| UNII_Ref = {{fdacite|correct|FDA}}
+| UNII = GTP1P30292
+| UNII_Comment = (anhydrous)
+| UNII2 = 961WP42S65
+| UNII2_Comment = (trihydrate)
+| UNII2_Ref = {{fdacite|correct|FDA}}
+| PubChem = 161067
+| SMILES = [K+].[K+].N#C[Fe-4](C#N)(C#N)(C#N)(C#N)C#N.[K+].[K+]
+| StdInChI=1S/6CN.Fe.4K.3H2O/c6*1-2;;;;;;;;/h;;;;;;;;;;;3*1H2/q6*-1;+2;4*+1;;;
+| StdInChIKey = UTYXJYFJPBYDKY-UHFFFAOYSA-N
+  }}
+| Section2       = {{Chembox Properties
+| Formula = K<sub>4</sub>[Fe(CN)<sub>6</sub>]
+| MolarMass = 368.35 g/mol (anhydrous)<br />422.388 g/mol (trihydrate)
+| Appearance = Light yellow, crystalline granules
+| Density = 1.85 g/cm<sup>3</sup> (trihydrate)
+| Solubility = ''trihydrate'' <br /> 28.9 g/100 mL (20&nbsp;°C)
+| SolubleOther = insoluble in [[ethanol]], [[diethyl ether|ether]]
+| MeltingPtC =
+| BoilingPtC =
+| BoilingPt_notes = (decomposes)
+| MagSus = &minus;130.0·10<sup>−6</sup> cm<sup>3</sup>/mol
+  }}
+| Section7       = {{Chembox Hazards
+| ExternalSDS =
+| MainHazards =
+| FlashPt = Non-flammable
+| GHSPictograms = {{GHS09}}
+| GHSSignalWord = Warning
+| HPhrases = {{H-phrases|411}}
+| PPhrases = {{P-phrases|}}
+| NFPA-H = 1
+| NFPA-F = 0
+| NFPA-R = 0
+| NFPA-S =
+| LD50 = 6400 mg/kg (oral, rat)<ref>https://chem.nlm.nih.gov/chemidplus/rn/13943-58-3 {{Dead link|date=March 2022}}</ref>
+  }}
+| Section8       = {{Chembox Related
+| OtherAnions = [[Potassium ferricyanide]]
+| OtherCations = [[Sodium ferrocyanide]]<br />[[Prussian blue]]
+  }}
+}}
+'''Potassium hexacyanidoferrate(II)''' is the [[inorganic compound]] with formula K<sub>4</sub>[Fe(CN)<sub>6</sub>]·3H<sub>2</sub>O. It is the potassium salt of the [[complex (chemistry)|coordination complex]] [Fe(CN)<sub>6</sub>]<sup>4−</sup>. This salt forms lemon-yellow [[monoclinic]] [[crystal]]s.
-'''Potassium ferrocyanide''' (K<sub>4</sub>Fe(CN)<sub>6</sub>&middot;3H<sub>2</sub>O), also known as yellow prussiate of potash or potassium hexacyanoferrate(II), is a [[complex (chemistry)|coordination compound]] forming lemon-yellow [[monoclinic]] [[crystal]]s at [[room temperature]] and decomposing at its boiling point. It is insoluble in [[ethanol|alcohol]] but a litre of water can dissolve just under three hundred [[gram]]s of the crystals, and the solution can react with acid to release [[hydrogen cyanide]] gas. The resulting hydrogen cyanide (HCN) boils at 26 &deg;[[Celsius|C]] and, being slightly [[lighter than air]], quickly [[evaporation|evaporates]] clear of the release point.
+==Synthesis==
-Potassium ferrocyanide is also one of two compounds present in [[ferroxyl indicator solution]] (along with [[phenolphthalein]]) which turns blue in the presence of Fe<sup>3+</sup> ions, and which can therefore be used to detect rust. It is possible to calculate the number of moles of Fe<sup>3+</sup> ions by using a [[colorimeter]].
+In 1752, the French chemist [[Pierre Macquer|Pierre Joseph Macquer]] (1718–1784) first reported the preparation of Potassium hexacyanidoferrate(II), which he achieved by reacting [[Prussian blue]] (iron(III) ferrocyanide) with [[potassium hydroxide]].<ref>{{cite journal |last1=Macquer |title=Éxamen chymique de bleu de Prusse |journal=Histoire de l'Académie Royale des Sciences …, § Mémoires de l'Académie royale des Sciences |date=1752 |pages=60–77 |url=https://www.biodiversitylibrary.org/item/88112#page/250/mode/1up |trans-title=Chemical examination of Prussian blue |language=fr}}
-On [[February 20]], [[2002]] four [[Morocco|Moroccans]] were arrested while in possession of detailed maps of the [[United States]] embassy in [[Rome]], the Rome water supply network, and four kilograms of potassium ferrocyanide.
+ From pp. 63-64:  ''"Après avoir essayé ainsi inutilement de décomposer le bleu de Prusse par les acides, … n'avoit plus qu'une couleur jaune un peu rousse."''  (After having tried so vainly to decompose Prussian blue by acids, I made recourse to alkalies.  I put a half ounce of this [Prussian] blue in a flask, and I poured on it ten ounces of a solution of nitre fixed by tartar [i.e., [[potassium nitrate]] (''nitre'') which is mixed with crude [[potassium bitartrate|cream of tartar]] and then ignited, producing potassium carbonate].  As soon as these two substances had been mixed together, I saw with astonishment that, without the aid of heat, the blue color had entirely disappeared; the powder [i.e., precipitate] at the bottom of the flask had only a rather gray color:  having put this vessel on a [[sand bath]] in order to heat the solution until it simmered, this gray color also disappeared entirely, and all that was contained in the flask, both the powder [i.e., precipitate] and the solution, had only a yellow color [that was] a little red.)</ref><ref>{{cite journal |last1=Munroe |first1=Charles E. |last2=Chatard |first2=Thomas M. |title=Manufactures: Chemicals and Allied Products |journal=Twelfth Census of the United States: Bulletins |date=1902 |issue=210 |pages=1–306 |url=https://books.google.com/books?id=8UIUAQAAMAAJ&pg=RA1-PA31}}; see p. 31.</ref>
-== See also ==
+===Modern production===
+Potassium hexacyanidoferrate(II) is produced industrially from [[hydrogen cyanide]],  [[iron(II) chloride]], and [[calcium hydroxide]], the combination of which affords Ca<sub>2</sub>[Fe(CN)<sub>6</sub>]·11H<sub>2</sub>O.  This solution is then treated with potassium salts to precipitate the mixed calcium-potassium salt CaK<sub>2</sub>[Fe(CN)<sub>6</sub>], which in turn is treated with [[potassium carbonate]] to give the tetrapotassium salt.<ref name=Ullmann>{{ cite encyclopedia |author1=Gail, E. |author2=Gos, S. |author3=Kulzer, R. |author4=Lorösch, J. |author5=Rubo, A. |author6=Sauer, M. |author7=Kellens, R. |author8=Reddy, J. |author9=Steier, N. |author10=Hasenpusch, W. | title = Cyano Compounds, Inorganic | encyclopedia = Ullmann's Encyclopedia of Industrial Chemistry |date=October 2011 | publisher = Wiley-VCH | location = Weinheim | doi = 10.1002/14356007.a08_159.pub3 |isbn=978-3527306732 }}</ref>
-*[[potassium ferricyanide]]
-*[[Prussian blue]]
+===Historical production===
+Historically, the compound was manufactured from nitrogenous organic material, iron filings, and potassium carbonate.<ref name=Wagner>{{cite book|last=Von Wagner|first=Rudolf|title=Manual of chemical technology|year=1897|publisher=D. Appleton & Co.|location=New York|page=474 & 477|url=https://archive.org/details/manualofchemical00wagnuoft}}</ref> Common [[nitrogen]] and [[carbon]] sources were [[torrefaction|torrified]] horn, leather scrap, [[offal]], or dried blood. It was also obtained commercially from gasworks spent oxide (purification of city gas from hydrogen cyanide).
+==Chemical reactions==
+Treatment of potassium hexacyanidoferrate(II) with [[nitric acid]] gives H<sub>2</sub>[Fe(NO)(CN)<sub>5</sub>].  After neutralization of this intermediate with [[sodium carbonate]], red crystals of [[sodium nitroprusside]] can be selectively crystallized.<ref>{{cite encyclopedia | author = Seel, F. | title = Sodium nitrosyl cyanoferrate | encyclopedia = Handbook of Preparative Inorganic Chemistry | edition = 2nd | editor = Brauer, G. | publisher = Academic Press | year = 1965 | location = New York | volume = 2 | page = 1768 | lccn = 63-14307 | url = https://www.scribd.com/doc/27443280/Handbook-of-Preparative-Inorganic-Chemistry-Vol-2-2d-Ed-George-Brauer | access-date = 2017-09-10 | archive-date = 2010-03-07 | archive-url = https://web.archive.org/web/20100307011411/http://www.scribd.com/doc/27443280/Handbook-of-Preparative-Inorganic-Chemistry-Vol-2-2d-Ed-George-Brauer | url-status = dead }}</ref>
+Upon treatment with [[chlorine]] gas, potassium hexacyanidoferrate(II) converts to [[potassium hexacyanidoferrate(III)]]:
+:2 K<sub>4</sub>[Fe(CN)<sub>6</sub>] + Cl<sub>2</sub> → 2 K<sub>3</sub>[Fe(CN)<sub>6</sub>] + 2 KCl
+This reaction can be used to remove potassium hexacyanidoferrate(II) from a solution.{{citation needed|date=April 2012}}
+A famous reaction involves treatment with ferric salts, most commonly [[Iron(III) chloride]], to give [[Prussian blue]]. In the reaction with Iron(III) chloride, producing [[Potassium chloride]] as a side-product:
+K<sub>4</sub>[Fe(CN)<sub>6</sub>] + 4 FeCl<sub>3</sub> → Fe<sub>4</sub>[Fe(CN)<sub>6</sub>]<sub>3</sub> + 12 KCl
+With the composition Fe{{su|p=III|b=4}}[Fe{{su|p=II}}([[Cyanide|CN]]){{su|b=6}}]{{su|b=3}}, this insoluble but deeply coloured material is the blue of [[blueprint]]ing, as well as on many famous paintings such as [[The Great Wave off Kanagawa]] and [[The Starry Night]].
+==Applications==
+Potassium hexacyanidoferrate(II) finds many niche applications in industry.  It and [[Sodium ferrocyanide|the related sodium salt]] are widely used as anticaking agents for both road salt and table salt. The potassium and sodium hexacyanidoferrates(II) are also used in the purification of tin and the separation of copper from molybdenum ores.  Potassium hexacyanidoferrate(II) is used in the production of wine and citric acid.<ref name=Ullmann/>
+In the EU, hexacyanidoferrates(II) (E 535–538) were, as of 2017, solely authorised in two food categories as salt additives.
+It can also be used in animal feed.<ref>{{cite web |title=EuSalt Expert Meeting on E 535 and E 536 as Feed Additives |url=https://eusalt.com/events/eusalt-expert-meeting-e-535-and-e-536-feed-additives |publisher=EUSalt |access-date=2018-12-06 |archive-date=2019-05-12 |archive-url=https://web.archive.org/web/20190512013808/https://eusalt.com/events/eusalt-expert-meeting-e-535-and-e-536-feed-additives |url-status=dead }}</ref>
+In the laboratory, potassium hexacyanidoferrate(II) is used to determine the concentration of [[potassium permanganate]], a compound often used in [[titration]]s based on [[redox]] reactions.  Potassium hexacyanidoferrate(II) 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 hexacyanidoferrate(II) can be used as a fertilizer for plants.{{citation needed|date=April 2012}}
+Prior to 1900, before the invention of the [[Castner process]], potassium hexacyanidoferrate(II) was the most important source of [[alkali metal]] [[Sodium cyanide|cyanides]].<ref name=Ullmann /> In this historical process, [[potassium cyanide]] was produced by decomposing potassium hexacyanidoferrate(II):<ref name=Wagner />
+K<sub>4</sub>[Fe(CN)<sub>6</sub>] → 4 KCN + FeC<sub>2</sub> + N<sub>2</sub>
+==Structure==
+Like other metal cyanides, solid potassium hexacyanidoferrate(II), both as the hydrate and anhydrous salts, has a complicated polymeric structure.  The polymer consists of octahedral [Fe(CN)<sub>6</sub>]<sup>4−</sup> centers crosslinked with K<sup>+</sup> ions that are bound to the CN [[ligand]]s.<ref>{{Cite journal |last1=Willans |first1=Mathew J. |last2=Wasylishen |first2=Roderick E. |last3=McDonald |first3=Robert |date=2009-05-18 |title=Polymorphism of Potassium Ferrocyanide Trihydrate as Studied by Solid-State Multinuclear NMR Spectroscopy and X-ray Diffraction |url=https://pubs.acs.org/doi/10.1021/ic802134j |journal=Inorganic Chemistry |language=en |volume=48 |issue=10 |pages=4342–4353 |doi=10.1021/ic802134j |pmid=19425611 |issn=0020-1669}}</ref>  The K<sup>+</sup>---NC linkages break when the solid is dissolved in water.{{clarify|date=May 2020}}{{citation needed|date=May 2020}}
+===Toxicity===
+The toxicity in rats is low, with [[lethal dose]] (LD<sub>50</sub>) at 6400&nbsp;mg/kg.<ref name=JTBaker>{{cite web | url = http://hazard.com/msds/mf/baker/baker/files/p5763.htm | title = POTASSIUM FERROCYANIDE MSDS Number: P5763 - Effective Date: 12/08/96 | publisher = J. T. Baker Inc. | access-date = 2012-04-08 | url-status = dead | archive-date = 2015-11-21 | archive-url = https://web.archive.org/web/20151121093949/http://hazard.com/msds/mf/baker/baker/files/p5763.htm }}</ref>{{Better source needed|date=July 2024}} The kidneys are the organ for ferrocyanide toxicity.<ref>{{cite journal |last1=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. |title=Re-evaluation of sodium ferrocyanide (E 535), potassium ferrocyanide (E 536) and calcium ferrocyanide (E 538) as food additives |journal=EFSA Journal |date=2018 |volume=16 |issue=7 |page=5374 |doi=10.2903/j.efsa.2018.5374 |pmid=32626000 |pmc=7009536 |url=https://www.efsa.europa.eu/en/efsajournal/pub/5374|doi-access=free }}</ref>
+==See also==
+*[[Ferrocyanide]]
+*[[Potassium hexacyanidoferrate(III)]]<ref>{{Cite journal |last1=Kosugi |first1=Nobuhiro |last2=Yokoyama |first2=Toshihiko |last3=Kuroda |first3=Haruo |date=May 1986 |title=Polarization dependence of XANES of square-planar Ni(CN)2−4 ion. A comparison with octahedral Fe(CN)4−6 and Fe(CN)3−6 ions |url=http://dx.doi.org/10.1016/0301-0104(86)85034-0 |journal=Chemical Physics |volume=104 |issue=3 |pages=449–453 |doi=10.1016/0301-0104(86)85034-0 |issn=0301-0104}}</ref>
+*[[Ferricyanide]]
+==References==
+{{Reflist}}
 ==External links==
-* [http://www.npi.gov.au/database/substance-info/profiles/29.html National Pollutant Inventory - Cyanide compounds fact sheet]
+* {{ cite web | url = http://www.npi.gov.au/substances/cyanide/index.html | publisher = National Pollutant Inventory Australia | title = Cyanide (inorganic) compounds fact sheet }}
+* {{cite web | url = http://blogs.rediff.com/thinko/2019/07/31/customers-can-rely-on-tata-salt-as-report-says-it-is-safe-to-consume/ | work = rediff.com | title = Potassium Ferrocyanide in Salt Is Entirely Safe To Consume }}{{Dead link|date=October 2022 |bot=InternetArchiveBot |fix-attempted=yes }}
+{{Potassium compounds}}
-{{Inorganic-compound-stub}}
+{{DEFAULTSORT:Potassium Ferrocyanide}}
 [[Category:Potassium compounds]]
-[[Category:Iron compounds]]
+[[Category:Iron(II) compounds]]
-[[Category:Cyanides]]
+[[Category:Cyano complexes]]
+[[Category:E-number additives]]
+[[Category:Nephrotoxins]]
-[[de:Kaliumhexacyanoferrat(II)]]
+[[Category:Iron complexes]]
-[[hu:Sárgavérlúgsó]]
-[[ru:Гексацианоферрат(II) калия]]

v t e Potassium compounds
H, (pseudo)halogens	KF KHF₂ KH KCl KClO KClO₃ KClO₄ KBr KBrO₃ KI KIO₃ KIO₄ KAt KCN KCNO KOCN KSCN
chalcogens	K₂O KOH K₂O₂ KO₂ KO₃ K₂S KHS K₂SO₃ KHSO₃ K₂SO₄ KHSO₄ KHSO₅ K₂S₂O₃ K₂S₂O₅ K₂S₂O₇ K₂S₂O₈ K₂Se K₂SeO₃ K₂SeO₄ K₂Te K₂TeO₃ K₂TeO₄ K₂Po
pnictogens	K₃N KNH₂ KN₃ KNO₂ KNO₃ K₃P KH₂PO₃ K₃PO₄ K₂HPO₄ KH₂PO₄ KPF₆ KAsO₂ K₃AsO₄ K₂HAsO₄ KH₂AsO₄
B, C group	B₄K₂O₇ K₂CO₃ KHCO₃ K₂SiO₃ K₂SiF₆ K₂Al₂O₄ K₂Al₂B₂O₇
transition metals	K₂PtCl₄ K₂Pt(CN)₄ K₂TiF₆ K₂PtCl₆ K₂ReCl₆ K ₂ReF ₆ KAsF₆ K₂ReBr₆ K ₂ReI ₆ K₂ZrF₆ K₄Fe(CN)₆ K₃Fe(CN)₆ K₃Fe(C₂O₄)₃ K₂FeO₄ K₂MnO₄ KMnO₄ K₃CrO₄ K₂CrO₄ K₃CrO₈ KCrO₃Cl K₂Cr₂O₇ K₂Cr₃O₁₀ K₂Cr₄O₁₃ K₄Mo₂Cl₈
organic	KHCO₂ KCH₃CO₂ KCF₃CO₂ K₂C₂O₄ KHC₂O₄ KC₁₂H₂₃O₂ KC₁₈H₃₅O₂ C₃H₂K₂O₄ C₄H₆KO₄ C₅H₇KO₄