Everything about Hydrogen Cyanide totally explained
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Hydrogen cyanide is a
chemical compound with
chemical formula HCN. A
solution of hydrogen cyanide in
water is called hydrocyanic acid. Hydrogen cyanide is a
colorless, very
poisonous, and highly
volatile liquid that
boils slightly above
room temperature at 26
°C (78.8
°F). HCN has a faint, bitter,
almond-like
odor that some people are unable to
detect due to a
genetic
trait. Hydrogen cyanide is weakly
acidic and partly
ionizes in solution to give the
cyanide anion, CN
–. The
salts of hydrogen cyanide are known as
cyanides. HCN is a highly valuable precursor to many chemical compounds ranging from polymers to pharmaceuticals.
Production and synthesis
Hydrogen cyanide is currently produced in large quantities by three processes. In the year 2000, 1.615 billion pounds (732,552 tons) were produced in the US.
(External Link
) The most important process for the production of hydrogen cyanide is the
Andrussov oxidation invented by
Leonid Andrussow in which
methane and
ammonia react in the presence of
oxygen at about 1200 °C over a
platinum catalyst:
» :2CH
4 + 2NH
3 + 3O
2 → 2HCN + 6H
2O
The energy needed for the reaction is provided by the part oxidation of methane and ammonia.
Of lesser importance is the
Degussa process (BMA process) in which no oxygen is added and the energy must be transferred indirectly through the reactor wall:
» :CH
4 + NH
3 → HCN + 3H
2
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:
» :CH(O)NH
2 → HCN + H
2O
In the laboratory, small amounts of HCN are produced by the addition of acids to cyanide salts of alkali metals:
» :H
+ + NaCN → HCN + Na
+
This reaction is sometimes the basis of accidental poisonings because the acid converts a nonvolatile cyanide salt into the gaseous HCN.
History
The first source for hydrogen cyanide was the reaction of acid on
ferrocyanides. The rising demand due to the use of cyanides for mining operations in the 1890s was met by the
Bleiby process.
George Thomas Beilby patented a method to produce hydrogen cyanide by passing
ammonia over glowing
coal in 1892. This method was used until
Hamilton Castner in 1894 developed a synthesis starting from coal, ammonia and
sodium yielding sodium cyanide, which reacts with acid to form gaseous HCN.
Reactions
HCN adds to
ketones and
aldehydes to give
cyanohydrins. Amino acids are prepared by this reaction; the essential
amino acid methionine is manufactured by this route.The cyanohydrin of
acetone is a precursor to
methyl methacrylate.
In
hydrocyanation, HCN adds to
alkenes to give nitriles. This reaction is employed to manufacture
adiponitrile, the precursor to
Nylon 66.
Occurrence and applications
Cyanide is used in
tempering steel,
dyeing,
explosives,
engraving, the production of
acrylic resin plastic, and other organic chemical products (eg: historically:
formic acid). The less toxic
ethyl acetate (C
4H
8O
2) has now largely replaced the use of cyanide in
insect killing jars. Cyanide is also being used for
capital punishment.
Fruits that have a pit, such as
cherries and
apricots,
bitter almonds and
apples, from which almond oil and flavoring are made, contain small amounts of
cyanohydrins such as
mandelonitrile (CAS#532-28-5). Such molecules slowly release hydrogen cyanide. Some
millipedes release hydrogen cyanide as a defense mechanism, as do certain insects such as some
burnet moths. Hydrogen cyanide is contained in the exhaust of vehicles, in
tobacco and wood smoke, and in smoke from burning nitrogen-containing
plastics.
100 g of crushed apple seeds can yield 219 mg of
Amygdalin which can generate ~10 mg of HCN.
HCN and the origin of life
Hydrogen cyanide has been discussed as a precursor to amino acids and nucleic acids. It is possible, for example, that HCN played a part in the
origin of life.
Leslie Orgel, among many researchers, has written extensively on the condensation 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 condensation of HCN.
Hydrogen cyanide as a poison and chemical weapon
» See also: cyanide poisoning
An HCN concentration of 300 mg/m
3 in air will kill a
human within a few minutes. The toxicity is caused by the
cyanide ion, which prevents
cellular respiration. Hydrogen cyanide (under the brand name
Zyklon B) was perhaps most infamously employed by the
Nazi regime in mid-20th century.
Hydrogen cyanide is commonly listed amongst
chemical warfare agents that cause general poisoning. As a substance listed under
Schedule 3 of the
Chemical Weapons Convention as a potential weapon which has large-scale industrial uses, manufacturing plants in signatory countries which produce more than 30 tonnes per year must be declared to, and can be inspected by, the
OPCW.
Hydrogen cyanide gas in air is explosive at concentrations over 5.6%, equivalent to 56,000
ppm.
Footnotes
Further Information
Get more info on 'Hydrogen Cyanide'.
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