Hydrogen cyanide

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Hydrogen cyanide
Chemical structure of hydrogen cyanide
Hydrogen cyanide
General
Systematic name Hydrogen cyanide
Other names Hydrocyanic acid
prussic acid,
formonitrile
formic anammonide
carbon hydride nitride
cyclon
Molecular formula CHN
SMILES C#N
Molar mass 27.03 g/mol
Appearance Colorless gas or pale blue
highly volatile liquid
CAS number 74-90-8
Properties
Density and phase 0.687 g/cm3, liquid.
Solubility in water Completely miscible.
Melting point -13.4 °C (259.75 K, 7.88 F)
Boiling point 26 °C (299.15 K, 78.8 F)
Acidity (pKa) 9.2 to 9.3
Structure
Molecular shape Linear
Dipole moment 2.98 D
Hazards
MSDS External MSDS
Main hazards Highly toxic, highly flammable.
NFPA 704
NFPA 704
fire diamond
NFPA 704 four-colored diamondHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazards (white): no code
4
4
2
Flash point −17.78 °C
Autoignition 538 °C
R/S statement R: Template:R12, Template:R26, Template:R27, Template:R28, Template:R32.
S: Template:S1, Template:S2, Template:S7, Template:S9, Template:S13, Template:S16,
Template:S28, Template:S29, Template:S45.
RTECS number MW6825000
Supplementary data page
Structure and
properties 		n, εr, etc.
Thermodynamic
data 		Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Other anions Hydrogen fluoride
Other cations Sodium cyanide
Potassium cyanide
Related compounds Cyanogen
Cyanogen chloride
trimethylsilyl cyanide
Except where noted otherwise, data are given for
materials in their standard state (at 25°C, 100 kPa)
Infobox disclaimer and references

Hydrogen cyanide is a chemical compound with chemical formula HCN. A solution of hydrogen cyanide in water is called hydrocyanic acid or Prussic acid. Pure hydrogen cyanide is a colorless, very poisonous, and highly volatile liquid that boils slightly above room temperature at 26 °C. Hydrogen cyanide has a faint, bitter, almond-like odor that some people are unable to smell due to a genetic trait. Hydrogen cyanide is weakly acidic and partly ionizes to become the cyanide ion CN– in aqueous solution, resulting in a colorless volatile liquid with the typical hydrogen cyanide odor. The salts of hydrogen cyanide are known as cyanides.

Production and synthesis

Currently Hydrogen cyanide is produced in large quantities by two processes. In the year 2000, 1,615 million pounds were produced in the US.[1]

In the Degussa process, ammonia and methane react at 1200 °C over a platinum catalyst:

CH4 + NH3 → HCN + 3H2

This reaction is akin to steam reforming, the reaction of methane and water. In the Andrussov process, oxygen is added

CH4 + NH3 + 1.5O2 → HCN + 3H2O

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 the nonvolatile salt into the gaseous HCN.

Reactions

1. HCN + ketone or aldehyde → cyanohydrin

Occurrence and applications

HCN is used to produce many valuable products including adiponitrile, the precursor to Nylon 66, acetone cyanohydrin, a precursor to methyl methacrylate, and the essential amino acid methionine.

Cyanide is used in tempering steel, dyeing, explosives, engraving, capital punishment, the production of acrylic resin plastic, and other organic chemical products (eg: historically: Formic Acid). The less toxic ethyl acetate (C4H8O2) has now largely replaced the use of cyanide in insect killing jars.

Fruits that have a pit, such as cherries or apricots, and bitter almonds, from which almond oil and flavoring are made, contain cyanohydrins such as mandelonitrile. Such molecules slowly release small quantities of hydrogen cyanide.[1],[2] Some millipedes release hydrogen cyanide as a defense mechanism[3], 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. Cyanide may be a cause of morbidity and mortality in fires.[citation needed]

Hydrogen cyanide as a chemical weapon

An HCN concentration of 300 parts per million in air will kill a human within a few minutes. The toxicity is caused by the cyanide ion. The mechanism of this toxicity, and the uses of the poison, are described in the Cyanide article. Hydrogen cyanide (under the brand name Zyklon B) was perhaps most infamously employed by Germany's mid-20th century Nazi regime as a method of mass-execution. Hydrogen cyanide is now listed under schedule 3 of the Chemical Weapons Convention.

Hydrogen cyanide is commonly listed amongst chemical warfare agents which cause general poisoning.[4] 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.

Although there have been no verified instances of this compound being used as a weapon, 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[5]. A solid compound that released hydrogen cyanide known as Zyklon B was used during World War II in the Nazi gas chambers of Auschwitz and Majdanek.[6]

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[7] . In 2003, Al Qaeda reportedly planned to attack the New York City Subway using hydrogen cyanide gas but aborted the attack for unknown reasons. [8]

Hydrogen cyanide gas in air is explosive at concentrations over 56,000 ppm.[citation needed]

Sources

  1. ^ J. Vetter (2000). "Plant cyanogenic glycosides". Toxicon. 38: 11–36. doi:10.1016/S0041-0101(99)00128-2.
  2. ^ D. A. Jones (1998). "Why are so many food plants cyanogenic?". Phytochemistry. 47: 155–162. doi:10.1016/S0031-9422(97)00425-1.
  3. ^ M. S. Blum, J. P. Woodring (1962). "Secretion of Benzaldehyde and Hydrogen Cyanide by the Millipede Pachydesmus crassicutis (Wood)". Science. 138: 512–513. doi:10.1126/science.138.3539.512.
  4. ^ "Hydrogen Cyanide". Organisation for the Prohibition of Chemical Weapons. Retrieved 2006-10-07.
  5. ^ http://www.bt.cdc.gov/agent/cyanide/basics/facts.asp
  6. ^ http://www.time.com/time/nation/article/0,8599,1205309,00.html
  7. ^ "Chronology of Aum Shinrikyo's CBW Activities" (pdf).
  8. ^ http://www.time.com/time/magazine/article/0,9171,1205478,00.html

See also

External links

Template:ChemicalSources


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