Potassium ferricyanide

Potassium ferricyanide is the chemical compound with the formula K3[Fe(CN)6]. This bright red salt contains the octahedrally coordinated [Fe(CN)6]3− ion.[2] It is soluble in water and its solution shows some green-yellow fluorescence. It was discovered in 1822 by Leopold Gmelin.[3][4]

Not to be confused with potassium ferrocyanide.
"Prussian red" redirects here. For pigment based on ferric oxide, see Venetian red.
Potassium ferricyanide
Names
IUPAC name
Potassium hexacyanoferrate(III)
Other names
Red prussiate of Potash,
Prussian red,
Potassium ferricyanide
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.033.916
EC Number
  • 237-323-3
21683
RTECS number
  • LJ8225000
UNII
  • InChI=1S/6CN.Fe.3K/c6*1-2;;;;/q6*-1;+3;3*+1 ☒N
    Key: BYGOPQKDHGXNCD-UHFFFAOYSA-N ☒N
  • InChI=1S/6CN.Fe.3K/c6*1-2;;;;/q6*-1;+3;3*+1
    Key: BYGOPQKDHGXNCD-UHFFFAOYAG
  • [K+].[K+].N#C[Fe-3](C#N)(C#N)(C#N)(C#N)C#N.[K+]
Properties
K3[Fe(CN)6]
Molar mass 329.24 g/mol
Appearance deep red crystals, sometimes small pellets, orange to dark red powder
Density 1.89 g/cm3, solid
Melting point 300 °C (572 °F; 573 K)
Boiling point decomposes
330 g/L ("cold water")
464 g/L (20 °C)
775 g/L ("hot water")[1]
Solubility slightly soluble in alcohol
soluble in acid
soluble in water
+2290.0·10−6 cm3/mol
Structure
monoclinic
octahedral at Fe
Hazards
GHS labelling:
GHS07: Exclamation mark
Warning
H302, H315, H319, H332, H335
P261, P264, P270, P271, P280, P301+P312, P302+P352, P304+P312, P304+P340, P305+P351+P338, P312, P321, P330, P332+P313, P337+P313, P362, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
1
0
0
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
2970 mg/kg (mouse, oral)
Safety data sheet (SDS) MSDS
Related compounds
Other anions
 Potassium ferrocyanide
Other cations
 Prussian blue
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)
Infobox references
Potassium ferricyanide milled
Potassium ferricyanide when milled has lighter color

Preparation

Potassium ferricyanide is manufactured by passing chlorine through a solution of potassium ferrocyanide. Potassium ferricyanide separates from the solution:

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

Structure

Like other metal cyanides, solid potassium ferricyanide has a complicated polymeric structure. The polymer consists of octahedral [Fe(CN)6]3− centers crosslinked with K+ ions that are bound to the CN ligands.[5] The K+---NCFe linkages break when the solid is dissolved in water.

Applications

The compound is also used to harden iron and steel, in electroplating, dyeing wool, as a laboratory reagent, and as a mild oxidizing agent in organic chemistry.

Blueprint, cyanotype, toner

The compound has widespread use in blueprint drawing and in photography (Cyanotype process). Several photographic print toning processes involve the use of potassium ferricyanide.It is often used as a mild bleach in a concentration of 10g/L to reduce film or print density.

Bleaching

Potassium ferricyanide was used as an oxidizing agent to remove silver from color negatives and positives during processing, a process called bleaching. Because potassium ferricyanide bleaches are environmentally unfriendly, short-lived, and capable of releasing hydrogen cyanide gas if mixed with high concentrations and volumes of acid, bleaches using ferric EDTA have been used in color processing since the 1972 introduction of the Kodak C-41 process. In color lithography, potassium ferricyanide is used to reduce the size of color dots without reducing their number, as a kind of manual color correction called dot etching.

Farmers Reducer

Ferricyanide is also used in black-and-white photography with sodium thiosulfate (hypo) to reduce the density of a negative or gelatin silver print where the mixture is known as Farmer's reducer; this can help offset problems from overexposure of the negative, or brighten the highlights in the print.[6]

Reagent in organic synthesis

Potassium ferricyanide is a used as an oxidant in organic chemistry.[7][8] It is an oxidant for catalyst regeneration in Sharpless dihydroxylations.[9][10]

Sensors and indicators

Potassium ferricyanide is also one of two compounds present in ferroxyl indicator solution (along with phenolphthalein) that turns blue (Prussian blue) in the presence of Fe2+ ions, and which can therefore be used to detect metal oxidation that will lead to rust. It is possible to calculate the number of moles of Fe2+ ions by using a colorimeter, because of the very intense color of Prussian blue.

In physiology experiments potassium ferricyanide provides a means increasing a solution's redox potential (E°' ~ 436 mV at pH 7). As such, it can oxidize reduced cytochrome c (E°' ~ 247 mV at pH 7) in isolated mitochondria. Sodium dithionite is usually used as a reducing chemical in such experiments (E°' ~ −420 mV at pH 7).

Potassium ferricyanide is used to determine the ferric reducing power potential of a sample (extract, chemical compound, etc.).[11] Such a measurement is used to determine of the antioxidant property of a sample.

Potassium ferricyanide is a component of amperometric biosensors as an electron transfer agent replacing an enzyme's natural electron transfer agent such as oxygen as with the enzyme glucose oxidase. It is an ingredient in commercially available blood glucose meters for use by diabetics.

Other

Potassium ferricyanide is combined with potassium hydroxide (or sodium hydroxide as a substitute) and water to formulate Murakami's etchant. This etchant is used by metallographers to provide contrast between binder and carbide phases in cemented carbides.

Prussian blue

Prussian blue, the deep blue pigment in blue printing, is generated by the reaction of K3[Fe(CN)6] with ferrous (Fe2+) ions as well as K4[Fe(CN)6] with ferric salts.[12]

In histology, potassium ferricyanide is used to detect ferrous iron in biological tissue. Potassium ferricyanide reacts with ferrous iron in acidic solution to produce the insoluble blue pigment, commonly referred to as Turnbull's blue or Prussian blue. To detect ferric (Fe3+) iron, potassium ferrocyanide is used instead in the Perls' Prussian blue staining method.[13] The material formed in the Turnbull's blue reaction and the compound formed in the Prussian blue reaction are the same.[14][15]

Safety

Potassium ferricyanide has low toxicity, its main hazard being that it is a mild irritant to the eyes and skin. However, under very strongly acidic conditions, highly toxic hydrogen cyanide gas is evolved, according to the equation:

6 H+ + [Fe(CN)6]3− → 6 HCN + Fe3+[16]

See also

References
  1. Kwong, H.-L. (2004). "Potassium Ferricyanide". In Paquette, L. (ed.). Encyclopedia of Reagents for Organic Synthesis. New York: J. Wiley & Sons. doi:10.1002/047084289X. hdl:10261/236866. ISBN 9780471936237.
  2. Sharpe, A. G. (1976). The Chemistry of Cyano Complexes of the Transition Metals. London: Academic Press.
  3. Gmelin, Leopold (1822). "Ueber ein besonderes Cyaneisenkalium, and über eine neue Reihe von blausauren Eisensalzen" [On a particular potassium iron cyanate, and on a new series of iron salts of cyanic acid]. Journal für Chemie und Physik (in German). 34: 325–346.
  4. Ihde, A.J. (1984). The Development of Modern Chemistry (2nd ed.). New York: Dover Publications. p. 153.
  5. Figgis, B. N.; Gerloch, M.; Mason, R. (1969). "The crystallography and paramagnetic anisotropy of potassium ferricyanide". Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences. 309 (1496): 91–118. Bibcode:1969RSPSA.309...91F. doi:10.1098/rspa.1969.0031. S2CID 96689342.
  6. Stroebel, L.; Zakia, R. D. (1993). "Farmer's Reducer". The Focal Encyclopedia of Photography. Focal Press. p. 297. ISBN 978-0-240-51417-8.
  7. Prill, E. A.; McElvain, S. M. (1935). "1-Methyl-2-Pyridone". Organic Syntheses. 15: 41. doi:10.15227/orgsyn.015.0041.
  8. Würfel, Hendryk; Jakobi, Dörthe (2018). "Syntheses of Substituted 2-Cyano-benzothiazoles". Organic Syntheses. 95: 177–191. doi:10.15227/orgsyn.095.0177.
  9. Gonzalez, Javier; Aurigemma, Christine; Truesdale, Larry (2002). "Synthesis of (+)-(1S,2R)- and (−)-(1R,2S)-trans-2-Phenylcyclohexanol via Sharpless Asymmetric Dihydroxylation (AD)". Organic Syntheses. 79: 93. doi:10.15227/orgsyn.079.0093.
  10. Oi, Ryu; Sharpless, K. Barry (1996). "3-[(1S)-1,2-Dihydroxyethyl]-1,5-Dihydro-3H-2,4-Benzodioxepine". Organic Syntheses. 73: 1. doi:10.15227/orgsyn.073.0001.
  11. Nakajima, Y., Sato, Y., & Konishi, T. (2007). Antioxidant Small Phenolic Ingredients in Inonotus obliquus (persoon) Pilat (Chaga). Chemical & Pharmaceutical Bulletin, 55(8), 1222–1276.
  12. Dunbar, K. R.; Heintz, R. A. (1997). "Chemistry of Transition Metal Cyanide Compounds: Modern Perspectives". Progress in Inorganic Chemistry. Progress in Inorganic Chemistry. Vol. 45. pp. 283–391. doi:10.1002/9780470166468.ch4. ISBN 9780470166468.
  13. Carson, F. L. (1997). Histotechnology: A Self-Instructional Text (2nd ed.). Chicago: American Society of Clinical Pathologists. pp. 209–211. ISBN 978-0-89189-411-7.
  14. Tafesse, F. (2003). "Comparative Studies on Prussian Blue or Diaquatetraamine-Cobalt(III) Promoted Hydrolysis of 4-Nitrophenylphosphate in Microemulsions" (PDF). International Journal of Molecular Sciences. 4 (6): 362–370. doi:10.3390/i4060362.
  15. Verdaguer, M.; Galvez, N.; Garde, R.; Desplanches, C. (2002). "Electrons at Work in Prussian Blue Analogues" (PDF). Electrochemical Society Interface. 11 (3): 28–32. doi:10.1002/chin.200304218.
  16. "MSDS for potassium ferricyanide" (PDF).

Further reading
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