| Potassium ferrocyanide | |
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Potassium hexacyanidoferrate(II) |
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Other names
yellow prussiate of potash, tetrapotassium ferrocyanide; potassium prussiate trihydrate; tetrapotassium hexacyanidoferrate (4-), trihydrate; potassium hexacyanidoferrate(II)[1] |
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| Identifiers | |
| CAS number | 13943-58-3 , (anhydrous) 14459-95-1 (trihydrate) |
| PubChem | 161067 |
| Properties | |
| Molecular formula | 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 |
69−71 °C |
| Boiling point |
400 °C (decomp) |
| Solubility in water | 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 |
0
1
0
|
| Flash point | Non-flammable |
| Related compounds | |
| Other anions | Potassium ferricyanide |
| Other cations | Sodium ferrocyanide Prussian blue |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 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.
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Potassium ferrocyanide is produced industrially from hydrogen cyanide, ferrous chloride, 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.[2]
The most 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.
Upon treatment with chlorine gas, it converts to potassium ferricyanide:
This reaction can be used to remove potassium ferrocyanide from a solution.[3] When the two are combined, the product is Prussian blue. Potassium ferrocyanide, potassium ferricyanide, and Prussian blue account for over 97% of cyanides in the environment.[4]
Potassium ferrocyanide finds many niche applications in industry. It and the related sodium salt are widely used as anti-caking agents for both road salt and table salt. The potassium and sodium ferrocyanides area 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.[2]
In the laboratory, potassium ferrocyanide is used to determine the concentration of potassium permanganate, a compound often used in titrations based on redoxreactions. Potassium ferrocyanide is used in a mixture with potassium ferricyanide and phosphate buffered solution (PBS) to provide a buffer for X-Gal, which is used to cleave Beta-galactosidase, 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. It is often used as a gardening technique.[5] In an experiment to test this aim, plants were either deprived of nitrogen or given a nitrogen-rich environment while all were exposed to potassium ferrocyanide and potassium ferricyanide. The plants were unable to sustain themselves solely on the cyanides, but the uptake of the cyanides did increase in the absence of nitrogen. Furthermore, the plants appeared to have different methods for the uptake of the two cyanides.[4]
Potassium ferrocyanide itself is nontoxic, although upon contact with strong acid it can release of toxic hydrogen cyanide gas. The lethal dose (LD50) in rats is low, at 6400 mg/kg.[6]
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