|IUPAC name||Hydrogen cyanide|
|Other names||Hydrocyanic acid
carbon hydride nitride
|Molar mass||27.03 g/mol|
|Appearance||Colorless gas or pale blue
highly volatile liquid
|Density||0.687 g/cm³, liquid.|
-13.4°C (259.75 K, 7.88°F)
25.6°C (299 K, 78°F)
|Solubility in water||Completely miscible.|
|Acidity (pKa)||9.2 - 9.3|
|Dipole moment||2.98 D|
|Main hazards||Highly toxic, highly flammable.|
|R-phrases||, , , , .|
, , , , , ,|
, , .
|Flash point||−17.78 °C|
|Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Hydrogen cyanide is a chemical compound with the formula HCN. It is a colorless, very poisonous, and highly volatile liquid that boils slightly above room temperature. The gas is explosive in air, at concentrations above 5.6 percent. A solution of hydrogen cyanide in water is called hydrocyanic acid, and its salts are called cyanides.
Given its toxicity, hydrogen cyanide is listed as a chemical warfare agent. It was the active ingredient in Zyklon B, an insecticide used by the Nazi regime for the mass murder of Jews in the gas chambers of Auschwitz, Majdanek, and other extermination camps.
On the other hand, HCN is a highly valuable precursor for the synthesis of many chemical compounds, ranging from polymers to pharmaceuticals. In the year 2000, an estimated 1,615 million pounds (732,552 tons) of this substance was produced in the United States.
Some fruits that have a pit (such as cherries and apricots), bitter almonds, and apple seeds contain small amounts of cyanohydrins such as mandelonitrile (CAS#532-28-5). Such molecules slowly decompose to release hydrogen cyanide.
Some have proposed that hydrogen cyanide may have played a part in the origin of life, in terms of being a possible precursor to amino acids and nucleic acids. Leslie Orgel, among other researchers, has written extensively on the condensation reactions of HCN. Although the relationship of these chemical reactions to the origin of life remains speculative, studies in this area have led to discoveries of new pathways to organic compounds derived from the condensation of HCN.
Currently, hydrogen cyanide is produced in large quantities by three processes. The most important of these processes is called Andrussov oxidation, invented by Leonid Andrussow. In this method, methane and ammonia react in the presence of oxygen at about 1200 °C over a platinum catalyst:
The energy needed for the reaction is provided by the part oxidation of methane and ammonia.
This reaction is akin to steam reforming, the reaction of methane and water.
In another process (practiced at BASF), formamide is heated and split into hydrogen cyanide and water:
In the laboratory, small amounts of HCN are produced by the addition of acids to cyanide salts of alkali metals:
This reaction has sometimes been the basis of accidental poisonings because the acid converts a nonvolatile cyanide salt into the gaseous HCN.
HCN combines with ketones and aldehydes to give cyanohydrins. Amino acids are prepared by this reaction. For instance, the essential amino acid methionine is manufactured by this route. The cyanohydrin of acetone is a precursor to methyl methacrylate.
Hydrogen cyanide is a valuable starting material for the synthesis of various organic compounds. Its main use is in the production of adiponitrile, which is then used to manufacture nylon. A second important application is for the synthesis of methyl methacrylate, which in turn is needed for the production of polymethyl methacrylate (PMMA) resins. In addition, HCN is used in tempering steel, dyeing, explosives, and engraving.
Zyklon B was an insecticide that releases gaseous hydrogen cyanide upon exposure to air. It gained notoriety for its use by the Nazi regime in the mid-twentieth century as a method of mass murder, in the gas chambers of Auschwitz and Majdanek during the Holocaust.
Hydrogen cyanide is commonly listed amongst chemical warfare agents that cause general poisoning. It is listed under Schedule 3 of the Chemical Weapons Convention as a potential weapon with large-scale industrial uses. As such, manufacturing plants in signatory countries that produce more than 30 metric tons per year must be declared to, and can be inspected by, the Organization for the Prohibition of Chemical Weapons (OPCW).
Although there have been no verified instances of this compound being used as a weapon in warfare, it has been reported that hydrogen cyanide may have been employed by Iraq in the war against Iran and against the Kurds in northern Iraq during the 1980s.
In 1995, a device was discovered in a restroom in the Kayabacho Tokyo subway station consisting of bags of sodium cyanide and sulfuric acid with a remote controlled motor to rupture them in what was believed to be an attempt to produce toxic amounts of hydrogen cyanide gas by the Aum Shinrikyo cult. In 2003, Al Qaeda reportedly planned to attack the New York City Subway using hydrogen cyanide gas but aborted the attack for unknown reasons.
All links retrieved January 22, 2018.
|Blood agents:||Cyanogen chloride (CK) – Hydrogen cyanide (AC)|
|Blister agents:||Lewisite (L) – Sulfur mustard gas (HD, H, HT, HL, HQ) – Nitrogen mustard gas (HN1, HN2, HN3)|
|Nerve agents:||G-Agents: Tabun (GA) – Sarin (GB) – Soman (GD) – Cyclosarin (GF) | V-Agents: VE – VG – VM – VX|
|Pulmonary agents:||Chlorine – Chloropicrin (PS) – Phosgene (CG) – Diphosgene (DP)|
|Incapacitating agents:||Agent 15 (BZ) – KOLOKOL-1|
|Riot control agents:||Pepper spray (OC) – CS gas – CN gas (mace) – CR gas|
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