Potassium ferrocyanide

Potassium ferrocyanide
Names
IUPAC name
Potassium hexacyanoferrate(II)
Other names
(Yellow) Prussiate of Potash,[1]
Potassium hexacyanoferrate (II) trihydrate,
Tetrapotassium ferrocyanide trihydrate,
Ferrate hexacyano tetrapotassium trihydrate[2]
Identifiers
13943-58-3 (anhydrous) Yes
14459-95-1 (trihydrate) 
PubChem 161067
Properties
C6N6FeK4
Molar mass 368.35 g/mol (anhydrous)
422.388 g/mol (trihydrate)
Appearance Light yellow, crystalline granules
Density 1.85 g/cm3 (trihydrate)
Melting point 69 to 71 °C (156 to 160 °F; 342 to 344 K)
Boiling point 400 °C (752 °F; 673 K) (decomposes)
trihydrate
28.9 g/100 mL (20 °C)
Solubility insoluble in ethanol, ether
Hazards
EU Index Not listed
R-phrases R32, R52, R53
S-phrases S50(B), S61
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
0
1
0
Flash point Non-flammable
6400 mg/kg (oral, rat)[3]
Related compounds
Other anions
 Potassium ferricyanide
Other cations
 Sodium ferrocyanide
Prussian blue
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Potassium ferrocyanide 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

Modern production

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.[4]

Historical production

Historically, the compound was manufactured from organically derived nitrogenous carbon sources, iron filings, and potassium carbonate.[5] Common nitrogen and carbon sources were torrified horn, leather scrap, offal, or dried blood.

Chemical reactions

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.[6]

Upon treatment with chlorine gas, potassium ferrocyanide converts to potassium ferricyanide:

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.

A famous reaction involves treatment with ferric salts to give Prussian blue. With the approximate composition KFe2(CN)6, this insoluble but deeply coloured material is the blue of blueprinting.

Applications

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.[4]

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.

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.[4] In this historical process, potassium cyanide was produced by decomposing potassium ferrocyanide:[5]

K4[Fe(CN)6] → 4 KCN + FeC2 + N2

Toxicity

Potassium ferrocyanide is nontoxic, although upon contact with strong acid it can release extremely toxic hydrogen cyanide gas. It is not decomposed to cyanide in the body. The toxicity in rats is low, with lethal dose (LD50) at 6400 mg/kg.[2]

See also

References

  1. ↑ https://play.google.com/books/reader?printsec=frontcover&output=reader&id=gXwPAAAAYAAJ&pg=GBS.PA8
  2. ↑ 2.0 2.1 "POTASSIUM FERROCYANIDE MSDS Number: P5763 - Effective Date: 12/08/96". J. T. Baker Inc. Retrieved 2012-04-08.
  3. ↑ http://chem.sis.nlm.nih.gov/chemidplus/rn/13943-58-3
  4. ↑ 4.0 4.1 4.2 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.
  5. ↑ 5.0 5.1 Von Wagner, Rudolf (1897). Manual of chemical technology. New York: D. Appleton & Co. p. 474 & 477.
  6. ↑ Seel, F. (1965). "Sodium Nitrosyl Cyanoferrate". In Brauer, G. Handbook of Preparative Inorganic Chemistry 2 (2nd ed.). New York: Academic Press. p. 1768. LCCN 63-14307.

External links