Potassium cyanide
Encyclopedia
Potassium cyanide is an inorganic compound
with the formula
K
CN
. 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.
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.
It is used by entomologists as a killing agent in collecting jars, as most insect
s succumb within seconds, minimizing damage of even highly fragile specimens.
, followed by evaporation
of the solution in a vacuum:
or by treating formamide
with potassium hydroxide:
Approximately 50,000 tons of potassium cyanide are produced yearly.
. 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.
(NaCN) are widely used in organic synthesis
for the preparation of nitrile
s and carboxylic acid
s, particularly in the von Richter reaction
.
, 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:
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.
:
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, convulsion
s may occur. Death occurs not by cardiac arrest
, but by hypoxia of neural tissue.
The lethal dose for potassium cyanide is 200-300 mg. 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
survived a potassium cyanide poisoning because his stomach acidity was unusually low.
A number of prominent persons were killed or committed suicide
using potassium cyanide, including members of the Black Hand Gang and members of the Nazi Party, such as Hermann Göring
and Heinrich Himmler
, World War II
era British agents
(using purpose-made suicide pill
s), and various religious cult suicides such as by the Peoples Temple
and Heaven's Gate
. Potassium cyanide (and other forms of cyanide) is a popular method of murder in fiction, especially in the books written by Agatha Christie
.
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
K
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
CN
Cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....
. This colorless crystalline compound, similar in appearance to sugar
Sugar
Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...
, is highly soluble in water. Most KCN is used in gold mining
Gold mining
Gold mining is the removal of gold from the ground. There are several techniques and processes by which gold may be extracted from the earth.-History:...
, organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
, and electroplating. Smaller applications include jewelry for chemical gilding
Gilding
The term gilding covers a number of decorative techniques for applying fine gold leaf or powder to solid surfaces such as wood, stone, or metal to give a thin coating of gold. A gilded object is described as "gilt"...
and buffing.
KCN is highly toxic. The moist solid emits small amounts of hydrogen cyanide due to hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
, which smells like bitter almonds. Not everyone, however, can smell this odor: the ability to do so is a genetic trait.
It is used by entomologists as a killing agent in collecting jars, as most insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s succumb within seconds, minimizing damage of even highly fragile specimens.
Production
KCN is produced by treating hydrogen cyanide with a 50% aqueous solution of potassium hydroxidePotassium hydroxide
Potassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...
, followed by evaporation
of the solution in a vacuum:
- HCN + KOH → KCN + H2O
or by treating formamide
Formamide
Formamide, also known as methanamide, is an amide derived from formic acid. It is a clear liquid which is miscible with water and has an ammonia-like odor. It is used primarily for manufacturing sulfa drugs and synthesizing vitamins and as a softener for paper and fiber...
with potassium hydroxide:
- HCONH2 + KOH → KCN + 2H2O
Approximately 50,000 tons of potassium cyanide are produced yearly.
Structure
In aqueous solution, KCN is dissociated into hydrated K+ ions and CN−Cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....
. 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.
Applications
KCN and its close relative sodium cyanideSodium cyanide
Sodium cyanide is an inorganic compound with the formula NaCN. This highly toxic colorless salt is used mainly in gold mining but has other niche applications...
(NaCN) are widely used in organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
for the preparation of nitrile
Nitrile
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, one example being super glue .Inorganic compounds containing the -C≡N group are not called...
s and carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...
s, particularly in the von Richter reaction
Von Richter reaction
The von Richter reaction is the chemical reaction of aromatic nitro compounds with potassium cyanide giving carboxylation ortho to the position of the former nitro group. The reaction is named after Victor von Richter.-Reaction mechanism:...
.
Potassium gold cyanide
In gold miningGold mining
Gold mining is the removal of gold from the ground. There are several techniques and processes by which gold may be extracted from the earth.-History:...
, 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
Sodium cyanide
Sodium cyanide is an inorganic compound with the formula NaCN. This highly toxic colorless salt is used mainly in gold mining but has other niche applications...
(NaCN, a close relative of potassium cyanide) to produce sodium gold cyanide (NaAu(CN2)).
Very few other methods exist for this extraction process.
Toxicity
KCN can be detoxified most efficiently with hydrogen peroxideHydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
:
- KCN + H2O2 → KOCNCyanateThe cyanate ion is an anion with the chemical formula written as [OCN]− or [NCO]−. In aqueous solution it acts as a base, forming isocyanic acid, HNCO. The cyanate ion is an ambidentate ligand, forming complexes with a metal ion in which either the nitrogen or oxygen atom may be the electron-pair...
+ H2O
Cyanide
Cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....
is a potent inhibitor of cellular respiration
Cellular respiration
Cellular respiration is the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products. The reactions involved in respiration are catabolic reactions that involve...
, acting on mitochondrial cytochrome c oxidase
Cytochrome c oxidase
The enzyme cytochrome c oxidase or Complex IV is a large transmembrane protein complex found in bacteria and the mitochondrion.It is the last enzyme in the respiratory electron transport chain of mitochondria located in the mitochondrial membrane...
and hence blocking oxidative phosphorylation
Oxidative phosphorylation
Oxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate . Although the many forms of life on earth use a range of different nutrients, almost all aerobic organisms carry out oxidative phosphorylation to produce ATP,...
. This prevents the body from oxidizing food to produce useful energy. Lactic acidosis
Lactic acidosis
Lactic acidosis is a physiological condition characterized by low pH in body tissues and blood accompanied by the buildup of lactate especially D-lactate, and is considered a distinct form of metabolic acidosis. The condition typically occurs when cells receive too little oxygen , for example...
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
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
in the blood. The effects of potassium and sodium cyanide
Sodium cyanide
Sodium cyanide is an inorganic compound with the formula NaCN. This highly toxic colorless salt is used mainly in gold mining but has other niche applications...
are identical. The person loses consciousness, and death eventually follows over a period of time. During this period, convulsion
Convulsion
A convulsion is a medical condition where body muscles contract and relax rapidly and repeatedly, resulting in an uncontrolled shaking of the body. Because a convulsion is often a symptom of an epileptic seizure, the term convulsion is sometimes used as a synonym for seizure...
s may occur. Death occurs not by cardiac arrest
Cardiac arrest
Cardiac arrest, is the cessation of normal circulation of the blood due to failure of the heart to contract effectively...
, but by hypoxia of neural tissue.
The lethal dose for potassium cyanide is 200-300 mg. 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
Grigori Rasputin
Grigori Yefimovich Rasputin was a Russian Orthodox Christian and mystic who is perceived as having influenced the latter days of the Russian Emperor Nicholas II, his wife Alexandra, and their only son Alexei...
survived a potassium cyanide poisoning because his stomach acidity was unusually low.
A number of prominent persons were killed or committed suicide
Suicide
Suicide is the act of intentionally causing one's own death. Suicide is often committed out of despair or attributed to some underlying mental disorder, such as depression, bipolar disorder, schizophrenia, alcoholism, or drug abuse...
using potassium cyanide, including members of the Black Hand Gang and members of the Nazi Party, such as Hermann Göring
Hermann Göring
Hermann Wilhelm Göring, was a German politician, military leader, and a leading member of the Nazi Party. He was a veteran of World War I as an ace fighter pilot, and a recipient of the coveted Pour le Mérite, also known as "The Blue Max"...
and Heinrich Himmler
Heinrich Himmler
Heinrich Luitpold Himmler was Reichsführer of the SS, a military commander, and a leading member of the Nazi Party. As Chief of the German Police and the Minister of the Interior from 1943, Himmler oversaw all internal and external police and security forces, including the Gestapo...
, World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
era British agents
Special Air Service
Special Air Service or SAS is a corps of the British Army constituted on 31 May 1950. They are part of the United Kingdom Special Forces and have served as a model for the special forces of many other countries all over the world...
(using purpose-made suicide pill
Suicide pill
A Cyanide pill is a pill, capsule, ampoule or tablet containing a fatally poisonous substance that a person ingests deliberately in order to quickly cause his/her own life to end...
s), and various religious cult suicides such as by the Peoples Temple
Peoples Temple
Peoples Temple was a religious organization founded in 1955 by Jim Jones that, by the mid-1970s, included over a dozen locations in California including its headquarters in San Francisco...
and Heaven's Gate
Heaven's Gate
Heaven's Gate may refer to:* Heaven's Gate , a religious group mostly known for a mass suicide in 1997* Heaven's Gate , a 1980 American movie* Heavens Gate , a German heavy metal band...
. Potassium cyanide (and other forms of cyanide) is a popular method of murder in fiction, especially in the books written by Agatha Christie
Agatha Christie
Dame Agatha Christie DBE was a British crime writer of novels, short stories, and plays. She also wrote romances under the name Mary Westmacott, but she is best remembered for her 66 detective novels and 14 short story collections , and her successful West End plays.According to...
.
External links
- International Chemical Safety Card 0671
- Hydrogen cyanide and cyanides (CICAD 61)
- National Pollutant Inventory - Cyanide compounds fact sheet
- NIOSH Pocket Guide to Chemical Hazards
- European Chemicals Bureau
- 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)