Potassium cyanide
| Potassium cyanide | |
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Potassium cyanide |
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| Identifiers | |
| CAS number | 151-50-8  |
| PubChem | 9032 |
| ChemSpider | 8681 |
| UNII | MQD255M2ZO |
| EC number | 205-792-3 |
| UN number | 1680 |
| RTECS number | TS8750000 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | KCN |
| Molar mass | 65.12 g/mol |
| Appearance | White crystalline solid deliquescent |
| Odor | faint, almond-like |
| Density | 1.52 g/cm3 |
| Melting point |
634.5 °C, 908 K, 1174 °F |
| Boiling point |
1625 °C, 1898 K, 2957 °F |
| Solubility in water | 71.6 g/100 ml (25 °C) 100 g/100 mL (100 °C) |
| Solubility in methanol | 4.91 g/100 mL (20 °C) |
| Solubility in glycerol | soluble |
| Solubility in formamide | 14.6 g/100 mL |
| Solubility in ethanol | 0.57 g/100mL |
| Solubility in hydroxylamine | 41 g/100 mL |
| Acidity (pKa) | 11.0 |
| Refractive index (nD) | 1.410 |
| Thermochemistry | |
| Std enthalpy of formation ΔfH |
−131.5 kJ/mol |
| Standard molar entropy S |
127.8 J K−1 mol−1 |
| Hazards | |
| MSDS | ICSC 0671 |
| EU Index | 006-007-00-5 |
| EU classification |  T+  N |
| R-phrases | R26/27/28, R32, R50/53 |
| S-phrases | (S1/2), S7, S28, S29, S45, S60, S61 |
| NFPA 704 |
 0
4
0
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| Flash point | Non-flammable |
| LD50 | 5–10 mg/kg (oral in rats, mice, rabbits)[1] |
| Related compounds | |
| Other anions | Potassium cyanate Potassium thiocyanate |
| Other cations | Sodium cyanide |
| Related compounds | Hydrogen cyanide |
 (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 cyanide is an inorganic compound with the formula KCN. This colorless crystalline compound, similar in appearance to sugar, is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller applications include jewelry for chemical gilding and buffing.[2]
KCN is highly toxic. The moist solid emits small amounts of hydrogen cyanide due to hydrolysis, which smells like bitter almonds. Not everyone, however, can smell this odor: the ability to do so is a genetic trait.[3]
It is used by entomologists as a killing agent in collecting jars, as most insects succumb within seconds, minimizing damage of even highly fragile specimens.
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Production [edit]
KCN is produced by treating hydrogen cyanide with a 50% aqueous solution of potassium hydroxide, followed by evaporation of the solution in a vacuum:[4]
- HCN + KOH → KCN + H2O
or by treating formamide with potassium hydroxide:
- HCONH2 + KOH → KCN + 2H2O
Approximately 50,000 tons of potassium cyanide are produced yearly.[2]
Structure [edit]
In aqueous solution, KCN is dissociated into hydrated K+ ions and CN−. As a solid, the salt crystallizes such that the cations and anions organize like Na+ and Cl− in NaCl. The cations and anions six-coordinate. Each K+ is linked to two pi-bonds of the CN− as well as two links each to C and N each. Since CN− is diatomic, the symmetry of the solid is lower than that in NaCl. The cyanide anions form sheets. The CN− ions rapidly rotate in the solid at ambient temperature such that the time averaged shape of the CN− ions is spherical.[5]
Applications [edit]
KCN and its close relative sodium cyanide (NaCN) are widely used in organic synthesis for the preparation of nitriles and carboxylic acids, particularly in the von Richter reaction.
Potassium gold cyanide [edit]
In gold mining, KCN forms the water-soluble salt potassium gold cyanide (or gold potassium cyanide) and potassium hydroxide from gold metal in the presence of oxygen (usually from the surrounding air) and water:
- 4 Au + 8 KCN + O2 + 2 H2O → 4 K[Au(CN)2] + 4 KOH
A similar process uses sodium cyanide (NaCN, a close relative of potassium cyanide) to produce sodium gold cyanide (NaAu(CN2)).
Very few other methods exist for this extraction process.[citation needed]
Toxicity [edit]
KCN can be detoxified most efficiently with hydrogen peroxide:[2]
- KCN + H2O2 → KOCN + H2O
Cyanide is a potent inhibitor of cellular respiration, acting on mitochondrial cytochrome c oxidase and hence blocking oxidative phosphorylation. This prevents the body from oxidizing food to produce useful energy. Lactic acidosis then occurs as a consequence of anaerobic metabolism. Initially, acute cyanide poisoning causes a red or ruddy complexion in the victim because the tissues are not able to use the oxygen in the blood. The effects of potassium and sodium cyanide are identical. The person loses consciousness, and death eventually follows over a period of time. During this period, convulsions may occur. Death occurs not by cardiac arrest, but by hypoxia of neural tissue.
The lethal dose for potassium cyanide is 200-300 mg.[6] The toxicity of potassium cyanide when ingested depends on the acidity of the stomach, because it must react with an acid to become hydrogen cyanide, the deadly form of cyanide. Grigori Rasputin may have survived a potassium cyanide poisoning because his stomach acidity was unusually low.[7]
A number of prominent persons were killed or committed suicide using potassium cyanide, including members of the Black Hand and members of the Nazi Party, such as Hermann Göring and Heinrich Himmler, World War II era British agents (using purpose-made suicide pills), computer scientist Alan Turing, and various religious cult suicides such as by the Peoples Temple and Heaven's Gate. Also members of the LTTE involved in the assassination of Indian prime minister Rajiv Gandhi committed suicide using potassium cyanide.
References [edit]
- ^ Bernard Martel. Chemical Risk Analysis: A Practical Handbook. Kogan, 2004, page 361. ISBN 1-903996-65-1.
- ^ a b c Andreas Rubo, Raf Kellens, Jay Reddy, Joshua Wooten, Wolfgang Hasenpusch "Alkali Metal Cyanides" in Ullmann's Encyclopedia of Industrial Chemistry 2006 Wiley-VCH, Weinheim, Germany. doi:10.1002/14356007.i01_i01
- ^ Online 'Mendelian Inheritance in Man' (OMIM) 304300
- ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
- ^ H. T. Stokes, D. L. Decker, H. M. Nelson, J. D. Jorgensen (1993). "Structure of potassium cyanide at low temperature and high pressure determined by neutron diffraction". Physical Review B 47 (17): 11082–11092. doi:10.1103/PhysRevB.47.11082..
- ^ John Harris Trestrail III. Criminal Poisoning - Investigational Guide for Law Enforcement, Toxicologists, Forensic Scientists, and Attorneys (2nd edition). pg 119
- ^ John Emsley. The Elements of Murder: A History of Poison. pg 73
External links [edit]
- International Chemical Safety Card 0671
- Hydrogen cyanide and cyanides (CICAD 61)
- National Pollutant Inventory - Cyanide compounds fact sheet
- NIOSH Pocket Guide to Chemical Hazards
- CSST (Canada)
- NIST Standard Reference Database
- Institut national de recherche et de sécurité (1997). "Cyanure de sodium. Cyanure de potassium". Fiche toxicologique n° 111, Paris:INRS, 6pp. (PDF file, in French)
