Hydrogen cyanide « Netica Solution

Hydrogen cyanide

September 4th, 2008

Hydrogen cyanide

IUPAC name
hydrogen cyanide
methanenitrile
hydridonitridocarbon

Other names
Hydrocyanic acid
prussic acid
formonitrile
formic anammonide
carbon hydride nitride
cyanane
cyclon

Identifiers

CAS number

RTECS number
MW6825000

SMILES

C#N

Properties

Molecular formula
HCN

Molar mass
27.03 g/mol

Appearance
Colorless gas or pale blue
highly volatile liquid

Density
0.687 g/cm³, liquid.

Melting point

-13.4°C (259.75 K, 7.88°F)

Boiling point

26°C (299.15 K, 78.8°F)

Solubility in water
Completely miscible.

Acidity (pKa)
9.2 - 9.3

Hazards

Main hazards
Highly toxic, highly flammable.

NFPA 704

4
4
2

R-phrases
R12, R26, R27, R28, R32.

S-phrases
(S1), (S2), S7, S9, S13, S16,
S28, S29, S45.

Flash point
−17.78 °C (−64.004 °F)

Related compounds

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 references

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.

Contents

1 Production and synthesis
- 1.1 History
2 Reactions
3 Occurrence and applications
4 HCN and the origin of life
5 Hydrogen cyanide as a poison and chemical weapon
6 Footnotes
7 References
8 See also
9 External links

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.

2CH4 + 2NH3 + 3O2 → 2HCN + 6H2O

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:

CH4 + NH3 → HCN + 3H2

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)NH2 → HCN + H2O

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 (C4H8O2) has now largely replaced the use of cyanide in insect killing jars. Hydrogen Cyanide is also being used for capital punishment in gas chambers in six states, all of which have other options available..

Fruits that have a pit, such as cherries, apricots, apples, and bitter almonds 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. 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.

Hydrogen cyanide can also be used to purify water. This is so because it affects the respiration of the bacteria and other germs in the water.

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.

Hydrogen cyanide as a poison and chemical weapon

See also: cyanide poisoning

An HCN concentration of 300 mg/m3 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 the 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

^ Online Mendelian Inheritance in Man, Cyanide, inability to smell
^ L. Andrussow (1935). “The catalytic oxydation of ammonia-methane-mixtures to hydrogen cyanide.”. Angewandte Chemie 48: 593–595.
^ F. Endter (1958). “Die technische Synthese von Cyanwasserstoff aus Methan und Ammoniak ohne Zusatz von Sauerstoff”. Chemie Ingenieur Technik 30 (5): 281–376. doi:10.1002/cite.330300506.
^ J. Vetter (2000). “Plant cyanogenic glycosides”. Toxicon. 38: 11–36. doi:10.1016/S0041-0101(99)00128-2.
^ D. A. Jones (1998). “Why are so many food plants cyanogenic?”. Phytochemistry 47: 155–162. doi:10.1016/S0031-9422(97)00425-1.
^ 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. PMID 17753947.
^ Matthews, C. N. “The HCN World: Establishing Protein-Nucleic Augucid Life via Hydrogen Cyanide Polymers” Cellular Origin and Life in Extreme Habitats and Astrobiology (2004), 6 (Origins : Genesis, Evoluation and Diversity of Life), 121-135.
^ Al-Azmi, A.; Elassar, A.-Z. A.; Booth, B. L. “The Chemistry of Diaminomaleonitrile and its Utility in Heterocyclic Synthesis” Tetrahedron (2003), 59, 2749-2763. CODEN: TETRAB ISSN:0040-4020
^ Hydrogen Cyanide
^ “Hydrogen Cyanide”. Organisation for the Prohibition of Chemical Weapons. Retrieved on 2006-10-07.
^ Documentation for Immediately Dangerous to Life or Health Concentrations (IDLHs) - 74908

References

Institut national de recherche et de sécurité (1997). “Cyanure d’hydrogène et solutions aqueuses”. Fiche toxicologique n° 4, Paris:INRS, 5pp. (PDF file, in French)

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