Potassium cyanide

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Potassium cyanide
IUPAC name
Potassium cyanide
3D model (JSmol)
ECHA InfoCard 100.005.267 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 205-792-3
PubChem CID
RTECS number
  • TS8750000
UN number 1680
  • InChI=1S/CN.K/c1-2;/q-1;+1 Yes check.svgY
  • InChI=1/CN.K/c1-2;/q-1;+1
  • [K+].[C-]#N
Molar mass 65.12 g/mol
AppearanceWhite crystalline solid
Odor faint, almond-like
Density 1.52 g/cm3
Melting point 634.5 °C (1,174.1 °F; 907.6 K)
Boiling point 1,625 °C (2,957 °F; 1,898 K)
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
37.0·10−6 cm3/mol
Std molar
127.8 JK1mol1
131.5 kJ/mol
GHS labelling:
GHS-pictogram-acid.svg GHS-pictogram-skull.svg GHS-pictogram-silhouette.svg GHS-pictogram-pollu.svg
H290, H300, H310, H330, H370, H372, H410
P260, P264, P273, P280, P284, P301+P310
NFPA 704 (fire diamond)
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
5 mg/kg (oral, rabbit)
10 mg/kg (oral, rat)
5 mg/kg (oral, rat)
8.5 mg/kg (oral, mouse) [1]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 5 mg/m3 [2]
REL (Recommended)
C 5 mg/m3 (4.7 ppm) [10-minute] [2]
IDLH (Immediate danger)
25 mg/m3 [2]
Safety data sheet (SDS) ICSC 0671
Related compounds
Other anions
Potassium cyanate
Potassium thiocyanate
Other cations
Sodium cyanide
Rubidium cyanide
lithium cyanide
caesium cyanide
Related compounds
Hydrogen cyanide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Potassium cyanide is a compound with the formula KCN. This colorless crystalline salt, similar in appearance to sugar, is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller applications include jewellery for chemical gilding and buffing. [4]

Potassium cyanide is highly toxic. The moist solid emits small amounts of hydrogen cyanide due to hydrolysis, which may smell like bitter almonds. [5] Not everyone, however, can smell cyanide; the ability to do so is a genetic trait. [6]

The taste of potassium cyanide has been described as acrid and bitter, with a burning sensation [7] similar to lye. [8]


KCN is produced by treating hydrogen cyanide with an aqueous solution of potassium hydroxide, followed by evaporation of the solution in a vacuum: [9]


About 50,000 tons of potassium cyanide are produced yearly. [4]

Historical production

Before 1900 and the invention of the Castner process, potassium cyanide was the most important source of alkali metal cyanides. [4] In this historical process, potassium cyanide was produced by decomposing potassium ferrocyanide: [10]

K4[Fe(CN)6] → 4 KCN + FeC2 + N2


In aqueous solution, KCN is dissociated into hydrated potassium (K+) ions and cyanide (CN) ions. The common form of solid KCN, stable at ambient pressure and temperature, has the same cubic crystal structure as sodium chloride, with each potassium ion surrounded by six cyanide ions, and vice versa. Despite the cyanide ions being diatomic, and thus less symmetric than chloride, they rotate so rapidly, their time-averaged shape is spherical. At low temperature and high pressure, this free rotation is hindered, resulting in a less symmetric crystal structure with the cyanide ions arranged in sheets. [11] [12]


KCN and sodium cyanide (NaCN) are widely used in organic synthesis for the preparation of nitriles and carboxylic acids, particularly in the von Richter reaction. It also finds use for the synthesis of hydantoins, which can be useful synthetic intermediates, when reacted with a carbonyl compound such as an aldehyde or ketone in the presence of ammonium carbonate.

KCN is used as a photographic fixer in the wet plate collodion process. [13] The KCN dissolves silver where it has not been made insoluble by the developer. This reveals and stabilizes the image, making it no longer sensitive to light. Modern wet plate photographers may prefer less toxic fixers, often opting for sodium thiosulfate, but KCN is still used.

Potassium gold cyanide

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 NaCN to produce sodium gold cyanide (NaAu(CN2)).


Potassium cyanide is a potent inhibitor of cellular respiration, acting on mitochondrial cytochrome c oxidase, hence blocking oxidative phosphorylation. 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 and sodium cyanide are identical, and symptoms of poisoning typically occur within a few minutes of ingesting the substance: the person loses consciousness, and brain death eventually follows. During this period the victim may suffer convulsions. Death is caused by cerebral hypoxia. The expected LD100 dose (human) for potassium cyanide is 200–300 mg while the median lethal dose LD50 is estimated at 140 mg. [14]

People who died by suicide or were killed using potassium cyanide include:

It is used by professional entomologists as a killing agent in collecting jars, as insects succumb within seconds to the HCN fumes it emits, thereby minimizing damage to even highly fragile specimens.

KCN can be detoxified most efficiently with hydrogen peroxide or with a solution of sodium hypochlorite. Such solutions should be kept alkaline whenever possible so as to eliminate the possibility of generation of hydrogen cyanide: [4]

KCN + H2O2 → KOCN + H2O

Related Research Articles

<span class="mw-page-title-main">Cyanide</span> Any molecule with a cyano group (–C≡N)

In chemistry, a cyanide is a chemical compound that contains a C≡N functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom.

In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively charged sodium ions and negatively charged chloride ions.

Hydrogen cyanide, sometimes called prussic acid, is a chemical compound with the formula HCN and structure H−C≡N. It is a colorless, extremely poisonous, and flammable liquid that boils slightly above room temperature, at 25.6 °C (78.1 °F). HCN is produced on an industrial scale and is a highly valued precursor to many chemical compounds ranging from polymers to pharmaceuticals. Large-scale applications are for the production of potassium cyanide and adiponitrile, used in mining and plastics, respectively. It is more toxic than solid cyanide compounds due to its volatile nature.

<span class="mw-page-title-main">Potassium ferrocyanide</span> Chemical compound

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.

<span class="mw-page-title-main">Sodium cyanide</span> Chemical compound

Sodium cyanide is a poisonous compound with the formula NaCN. It is a white, water-soluble solid. Cyanide has a high affinity for metals, which leads to the high toxicity of this salt. Its main application, in gold mining, also exploits its high reactivity toward metals. It is a moderately strong base.

Acetonitrile, often abbreviated MeCN, is the chemical compound with the formula CH3CN and structure H3C−C≡N. This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture. It is used as a polar aprotic solvent in organic synthesis and in the purification of butadiene. The N≡C−C skeleton is linear with a short C≡N distance of 1.16 Å.

<span class="mw-page-title-main">Potassium ferricyanide</span> Chemical compound

Potassium ferricyanide is the chemical compound with the formula K3[Fe(CN)6]. This bright red salt contains the octahedrally coordinated [Fe(CN)6]3− ion. It is soluble in water and its solution shows some green-yellow fluorescence. It was discovered in 1822 by Leopold Gmelin.

Cyanogen is the chemical compound with the formula (CN)2. The simplest carbon nitride, it is a colorless and highly toxic gas with a pungent odor. The molecule is a pseudohalogen. Cyanogen molecules consist of two CN groups – analogous to diatomic halogen molecules, such as Cl2, but far less oxidizing. The two cyano groups are bonded together at their carbon atoms: N≡C‒C≡N, although other isomers have been detected. The name is also used for the CN radical, and hence is used for compounds such as cyanogen bromide (NCBr) (but see also Cyano radical.)

<span class="mw-page-title-main">Cyanohydrin</span> Functional group in organic chemistry

In organic chemistry, a cyanohydrin or hydroxynitrile is a functional group found in organic compounds in which a cyano and a hydroxy group are attached to the same carbon atom. The general formula is R2C(OH)CN, where R is H, alkyl, or aryl. Cyanohydrins are industrially important precursors to carboxylic acids and some amino acids. Cyanohydrins can be formed by the cyanohydrin reaction, which involves treating a ketone or an aldehyde with hydrogen cyanide (HCN) in the presence of excess amounts of sodium cyanide (NaCN) as a catalyst:

In organic chemistry, a nitrile is any organic compound that has a −C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, including methyl cyanoacrylate, used in super glue, and nitrile rubber, a nitrile-containing polymer used in latex-free laboratory and medical gloves. Nitrile rubber is also widely used as automotive and other seals since it is resistant to fuels and oils. Organic compounds containing multiple nitrile groups are known as cyanocarbons.

Cyanogen chloride is a highly toxic chemical compound with the formula CNCl. This linear, triatomic pseudohalogen is an easily condensed colorless gas. More commonly encountered in the laboratory is the related compound cyanogen bromide, a room-temperature solid that is widely used in biochemical analysis and preparation.

<span class="mw-page-title-main">Mercury(II) cyanide</span> Chemical compound

Mercury(II) cyanide, also known as mercuric cyanide, is a poisonous compound of mercury and cyanide. It is an odorless, toxic white powder. It is highly soluble in polar solvents such as water, alcohol, and ammonia; slightly soluble in ether; and insoluble in benzene and other hydrophobic solvents.

The Gattermann reaction, (also known as the Gattermann formylation and the Gattermann salicylaldehyde synthesis) is a chemical reaction in which aromatic compounds are formylated by a mixture of hydrogen cyanide (HCN) and hydrogen chloride (HCl) in the presence of a Lewis acid catalyst such as AlCl3. It is named for the German chemist Ludwig Gattermann and is similar to the Friedel–Crafts reaction.

<span class="mw-page-title-main">Zinc cyanide</span> Chemical compound

Zinc cyanide is the inorganic compound with the formula Zn(CN)2. It is a white solid that is used mainly for electroplating zinc but also has more specialized applications for the synthesis of organic compounds.

Acetone cyanohydrin (ACH) is an organic compound used in the production of methyl methacrylate, the monomer of the transparent plastic polymethyl methacrylate (PMMA), also known as acrylic. It liberates hydrogen cyanide easily, so it is used as a source of such. For this reason, this cyanohydrin is also highly toxic.

<span class="mw-page-title-main">Cadmium cyanide</span> Chemical compound

Cadmium cyanide is an inorganic compound with the formula Cd(CN)2. It is a white crystalline compound that is used in electroplating. It is very toxic, along with other cadmium and cyanide compounds.

Cobalt(II) cyanide is the inorganic compound with the formula Co(CN)2. It is coordination polymer that has attracted intermittent attention over many years in the area of inorganic synthesis and homogeneous catalysis.

<span class="mw-page-title-main">Ammonium cyanide</span> Chemical compound

Ammonium cyanide is an unstable inorganic compound with the formula NH4CN.

Potassium dicyanoaurate is an inorganic compound with formula K[Au(CN)2]. It is a colorless to white solid that is soluble in water and slightly soluble in alcohol. The salt itself is often not isolated, but solutions of the dicyanoaurate ion ([Au(CN)2]) are generated on a large scale in the extraction of gold from its ores.

Nickel dicyanide is the inorganic compound with a chemical formula Ni(CN)2. It is a gray-green solid that is insoluble in most solvents.


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  6. Online Mendelian Inheritance in Man (OMIM): 304300
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