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Potassium cyanide

Potassium cyanide
CAS number 151-50-8
EINECS number 205-792-3
RTECS number TS8750000
Molecular formula KCN
Molar mass 65.12 g/mol
Melting point


Solubility in other solvents 71.6 g/100 ml (25°C)
Std enthalpy of
−131.5 kJ/mol
Standard molar
127.8 J.K–1.mol–1
EU classification Very toxic (T+)
Dangerous for the environment (N)
R-phrases R26/27/28, R32
S-phrases (S1/2), S7, S28, S29
S45, S60, S61
LD50 5–10 mg/kg (oral in rats, mice, rabbits)[1]
Related Compounds
Other cations Sodium cyanide
Related compounds Hydrogen cyanide
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Potassium cyanide is the inorganic compound with the formula KCN. This colorless crystalline compound, similar in appearance to sugar, is highly soluble in water. The vast majority of KCN is used in gold mining followed by use in organic synthesis, and electroplating. Smaller applications include jewelry for chemical gilding and buffing.

Highly toxic, KCN is odorless but due to hydrolysis, solids emit small amounts of hydrogen cyanide, which smells like bitter almonds (not everyone can smell it—the ability thereof is due to a genetic trait.[2]). It is also used by entomologists as a killing agent in collecting jars, as most insects succumb within seconds, minimizing damage of even the most fragile types.



KCN is produced by treating hydrogen cyanide with potassium hydroxide.[3] Approximately 50,000 tons are produced yearly (the production of sodium cyanide is 10x that amount). It is detoxified most efficiently with hydrogen peroxide:[3]

KCN + H2O2 → KOCN + H2O


In gold mining, KCN and NaCN form water-soluble salts from gold metal in the presence of air:

4 Au + 8 KCN + O2 + 2 H2O → [Au(CN)2]- + 4 OH-

Very few methods exist for this extraction process.

KCN and the related NaCN are widely used in organic synthesis for the preparation of nitriles and carboxylic acids. Illustrative is the Von Richter reaction.


Main article: Cyanide poisoning

Cyanide salts are among the most rapidly acting of all known poisons.[citation needed] Cyanide is a potent inhibitor of cellular respiration, acting on mitochondrial cytochrome c oxidase and hence blocking oxidative phosphorylation. This prevents the body from oxidising 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 cyanide are virtually identical to sodium cyanide. Once more than 100–200 mg of potassium cyanide is absorbed, consciousness is lost within one minute, sometimes within 10 seconds, depending on the person involved and the amount of food present in the stomach.[citation needed] After a span of about 45 minutes, the body goes into a state of coma or deep sleep and the person may die within two hours if not treated medically. During this period, convulsions may occur. Death occurs mainly by cardiac arrest.

A number of prominent Nazis, including Hermann Goering and Heinrich Himmler, committed suicide using lethal pills which contained potassium cyanide.[4] The substance was also used in the 1978 mass murder/suicide of over 900 people at Jonestown, Guyana.[5]

In fiction

Main article: Cyanide poisoning

Potassium cyanide (and other forms of cyanide) often appear in fiction. In crime fiction it is a popular choice as a murder weapon.


  • 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)
  • The Landlady by Roald Dahl
  1. ^ Bernard Martel. Chemical Risk Analysis: A Practical Handbook. Kogan, 2004, page 361. ISBN 1903996651.
  2. ^ Online 'Mendelian Inheritance in Man' (OMIM) 304300
  3. ^ a b Andreas Rubo, Raf Kellens, Jay Reddy, Norbert Steier, Wolfgang Hasenpusch "Alkali Metal Cyanides" in Ullmann's Encyclopedia of Chemical Technology 2006 Wiley-VCH Verlag GmbH, Weinheim, Germany.ISBN: 10.1002/14356007.i01 i01
  4. ^ "Anderson Cooper 360 Degrees: Police Continue Search for Child Pornographer; Hermann Goering's Suicide Solved?; Atlanta Bride-to-be Still Missing; Massachusetts Money Find a Hoax?" (Transcript),, 29 April 2005. Retrieved on 2007-11-09. 
  5. ^ Text and first-hand account audio recording #4 indicate it was cyanide and bitter, respectively.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Potassium_cyanide". A list of authors is available in Wikipedia.
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