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 | |
| Names | |
|---|---|
| IUPAC name Potassium hexacyanoferrate(III) | |
| Other names Prussian red Potassium ferricyanide | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider |
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| ECHA InfoCard | 100.033.916 |
| EC Number |
|
| 21683 | |
| RTECS number |
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| UNII | |
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| |
| 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 inalcohol soluble inacid soluble in water |
| +2290.0·10−6 cm3/mol | |
| Structure | |
| monoclinic | |
| octahedral at Fe | |
| Hazards | |
| GHS labelling: | |
 | |
| 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) | |
| Flash point | Non-flammable |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 2970 mg/kg (mouse, oral) |
| Safety data sheet (SDS) | MSDS |
| Related compounds | |
Otheranions | Potassium ferrocyanide |
Othercations | Prussian blue |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Potassium ferricyanide is thechemical compound with the formula K3[Fe(CN)6]. This bright red salt contains theoctahedrallycoordinated[Fe(CN)6]3− ion.[2] It is soluble in water and its solution shows some green-yellowfluorescence. It was discovered in 1822 byLeopold Gmelin.[3][4]
Potassium ferricyanide is manufactured by passingchlorine through asolution ofpotassium ferrocyanide. Potassium ferricyanide separates from the solution:
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 CNligands.[5] The K+---NCFe linkages break when the solid is dissolved in water.
The compound is also used tohardeniron andsteel, inelectroplating,dyeingwool, as alaboratoryreagent, and as a mildoxidizing agent inorganic chemistry.
The compound has widespread use inblueprint drawing and inphotography (Cyanotype process). Severalphotographic 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.
Potassium ferricyanide was used as anoxidizing agent to removesilver 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 ferricEDTA have been used in color processing since the 1972 introduction of the KodakC-41 process. Incolor 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.
Ferricyanide is also used in black-and-white photography withsodium thiosulfate (hypo) to minimize the density of anegative orgelatin silver print where the mixture is known as Farmer's reducer. This reagent can help offset problems fromoverexposure of the negative, or brighten the highlights in the print.[6]
Potassium ferricyanide is a used as an oxidant in organic chemistry.[7][8] It is an oxidant for catalyst regeneration inSharpless dihydroxylations.[9][10]
Potassium ferricyanide is also one of two compounds present inferroxyl indicator solution (along withphenolphthalein) 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 acolorimeter, because of the very intense color ofPrussian blue.
In physiology experiments potassium ferricyanide provides a means increasing a solution'sredox 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 theantioxidant property of a sample.
Potassium ferricyanide is a component of amperometricbiosensors as anelectron transfer agent replacing an enzyme's natural electron transfer agent such asoxygen as with theenzymeglucose oxidase. It is an ingredient in commercially available bloodglucose meters for use bydiabetics.
Potassium ferricyanide is combined withpotassium hydroxide (orsodium 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, 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]
Inhistology, 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 orPrussian blue. To detect ferric (Fe3+) iron, potassiumferrocyanide is used instead in thePerls' 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]
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 toxichydrogen cyanide gas is evolved, according to the equation:
For example, it will react with diluted sulfuric acid under heating formingpotassium sulfate,ferric sulfate and hydrogen cyanide.
This will not occur with concentrated sulfuric acid as hydrolysis toformic acid and dehydration tocarbon monoxide will take place instead.[17]
