Editing Potassium ferrocyanide

{{Short description|Chemical compound}}
{{Distinguish|potassium ferricyanide}}
{{chembox
| Verifiedfields = changed
| Watchedfields  = changed
| verifiedrevid  = 444997361
| Name           = Potassium hexacyanidoferrate(II)
| ImageFile1     = Structure of potassium ferrocyanide.png
| ImageClass1 = skin-invert-image
| ImageFile2     = Potassium Ferrocyanide.png
| ImageClass2 = bg-transparent
| 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=ejk/>
 }}
| 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 = 1.6—3.2g/kg}}
| 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.

==Synthesis==

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}} 
 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>

===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>

===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: 

3 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.<ref name="ejk" />

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>

Potassium ferrocyanide is a component of ''white gunpowder'' or ''Augendre's powder'', a [[blasting powder]] of high energy.<ref>{{cite book |last1=Fay |first1=Albert |title=A Glossary of the Mining and Mineral Industry |date=1918 |publisher=[[United States Bureau of Mines]] |location=Washington, DC |page=741 |edition=1949}}</ref> It comprises 28 parts yellow potassium ferrocyanide, 23 parts cane sugar, and 49 parts of [[potassium chlorate]], mixed under [[absolute alcohol]] to prevent premature detonation.<ref>{{cite book |last= |first= |date= |title=Chemischen Technologie |url= |trans-title=A Handbook of Chemical Technolgie|language=German |translator-last1=Crookes |translator-first1=Willliam |translator-link1=William Crookes|location=New York |publisher=[[D. Appleton & Company]] |page= 155|edition=1872}}</ref><ref>{{cite book |last1=Brannt |first1=William T. (William Theodore) |last2=Wahl |first2=William H. (William Henry) |title=The Techno-chemical receipt book |date=1919 |publisher=Henry Carey Baird & Co. |location=New York |page=30 |url=https://archive.org/details/technochemicalre00bran/page/30/mode/1up}}</ref>

==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 1.6—3.2g/kg.<ref name=ejk>{{cite book |last1=Kopras |first1=Elizabeth J. |editor1-last=Bingham |editor1-first=Eula |editor2-last=Cohrssen |editor2-first=Barbara |editor1-link=Eula Bingham |title=Patty's Toxicology |date=2012 |publisher=[[Wiley (publisher)|Wiley]] |location=Hoboken, NJ |page=990 |edition=6 |volume=1|isbn=978-0-470-41081-3}}</ref> 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==
* {{ 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 }}
* [https://labphoto.tumblr.com/post/107528318273/a-large-crystal-of-potassium-ferrocyanide Photo] of large potassium ferrocyanide crystals

{{Potassium compounds}}

{{DEFAULTSORT:Potassium Ferrocyanide}}
[[Category:Potassium compounds]]
[[Category:Iron(II) compounds]]
[[Category:Cyano complexes]]
[[Category:E-number additives]]
[[Category:Nephrotoxins]]
[[Category:Iron complexes]]