Cyanide poisoning occurs when a living organism is exposed to a compound that produces cyanide ions (CN −) when dissolved in water. Common poisonous cyanide ...
Hydrogen cyanide
From Wikipedia, the free encyclopedia
Hydrogen cyanide
 |
|
|
| Names |
IUPAC name
- Formonitrile[1] (substitutive)
- Hydridonitridocarbon[2] (additive)
|
Other names
- Formic anammonide
- Hydrocyanic acid
- Prussic acid
- Methanenitrile
|
| Identifiers |
|
|
74-90-8  |
| 3DMet |
B00275 |
| ChEBI |
CHEBI:18407  |
| ChemSpider |
748 |
| EC number |
200-821-6 |
|
|
| Jmol-3D images |
Image |
| KEGG |
C01326 |
| MeSH |
Hydrogen+Cyanide |
| PubChem |
768 |
| RTECS number |
MW6825000 |
|
|
| UNII |
2WTB3V159F |
| UN number |
1051 |
| Properties |
|
|
CHN |
| Molar mass |
27.03 g·mol−1 |
| Appearance |
Very pale, blue, transparent liquid or colorless gas |
| Odor |
Oil of bitter almond |
| Density |
0.687 g mL−1 |
| Melting point |
−14 to −12 °C; 7 to 10 °F; 259 to 261 K |
| Boiling point |
25.6 to 26.6 °C; 78.0 to 79.8 °F; 298.7 to 299.7 K |
|
|
Miscible |
| Solubility in ethanol |
Miscible |
| Vapor pressure |
630 mmHg (20°C)[3] |
|
|
75 μmol Pa−1 kg−1 |
| Acidity (pKa) |
9.21[4] |
| Basicity (pKb) |
4.79 |
|
|
1.2675 [5] |
| Viscosity |
201 μPa s |
| Structure |
|
|
Linear |
|
|
2.98 D |
| Thermochemistry |
|
|
71.00 kJ K−1 mol−1 (at 27 °C)[6] |
|
|
113.01 J K−1 mol−1 |
|
|
109.9 kJ mol−1 |
|
|
-426.5 kJ mol−1 |
| Hazards |
| EU classification |
 F+  T+  N |
| R-phrases |
R12, R26/27/28, R50/53 |
| S-phrases |
(S1/2), S16, S36/37, S38, S45, S53, S59, S61 |
| NFPA 704 |
|
| Flash point |
−17.8 °C (0.0 °F; 255.3 K) |
|
|
538 °C (1,000 °F; 811 K) |
| Explosive limits |
5.6% - 40.0%[3] |
| Lethal dose or concentration (LD, LC): |
|
|
501 ppm (rat, 5 min)
323 ppm (mouse, 5 min)
275 ppm (rat, 15 min)
170 ppm (rat, 30 min)
160 ppm (rat, 30 min)
323 ppm (rat, 5 min)[7] |
|
|
200 ppm (mammal, 5 min)
36 ppm (mammal, 2 hr)
107 ppm (human, 10 min)
759 ppm (rabbit, 1 min)
759 ppm (cat, 1 min)
357 ppm (human, 2 min)
179 ppm (human, 1 hr)[7] |
| US health exposure limits (NIOSH): |
|
|
TWA 10 ppm (11 mg/m3) [skin][3] |
|
|
ST 4.7 ppm (5 mg/m3) [skin][3] |
|
|
50 ppm[3] |
| Related compounds |
Related alkanenitriles
|
|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|
 verify (what is:  / ?) |
| Infobox references |
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Hydrogen cyanide (
HCN), sometimes called
prussic acid, is an
organic compound[8] with the
chemical formula HCN. It is a
colorless, extremely
poisonous liquid that
boils slightly above
room temperature, at 25.6 °C (78.1 °F).
[9] HCN is produced on an industrial scale and is a highly valuable precursor to many chemical compounds ranging from
polymers to pharmaceuticals.
Structure and general properties
Hydrogen cyanide is a linear molecule, with a
triple bond between carbon and nitrogen. A minor
tautomer of HCN is HNC,
hydrogen isocyanide.
Hydrogen cyanide is weakly
acidic with a
pKa of 9.2. It partially
ionizes in water solution to give the
cyanide anion, CN
−. A
solution of hydrogen cyanide in
water, represented as HCN, is called
hydrocyanic acid. The
salts of the cyanide anion are known as cyanides.
HCN has a faint
bitter almond-like
odor that some people are unable to
detect owing to a
genetic trait.
[10] The
volatile compound has been used as inhalation
rodenticide and human poison, as well as for killing whales.
[11] Cyanide ions interfere with iron-containing respiratory enzymes.
History of discovery
Hydrogen cyanide was first isolated from a blue pigment (
Prussian blue) which had been known since 1704 but whose structure was unknown. It is now known to be a
coordination polymer with a complex structure and an empirical formula of hydrated ferric ferrocyanide. In 1752, the French chemist
Pierre Macquer made the important step of showing that Prussian blue could be converted to
iron oxide plus a volatile component and that these could be used to reconstitute it.
[12]
The new component was what we now know as hydrogen cyanide. Following
Macquer's lead, it was first prepared from Prussian blue by the Swedish
chemist
Carl Wilhelm Scheele in 1782,
[13] and was eventually given the German name
Blausäure (
lit.
"Blue acid") because of its acidic nature in water and its derivation
from Prussian blue. In English it became known popularly as
Prussic acid.
In 1787 the French chemist
Claude Louis Berthollet showed that Prussic acid did not contain oxygen,
[14] an important contribution to acid theory, which had hitherto postulated that acids must contain oxygen
[15] (hence the name of
oxygen itself, which is derived from Greek elements that mean "acid-former" and are likewise
calqued into German as
Sauerstoff). In 1811
Joseph Louis Gay-Lussac prepared pure, liquified hydrogen cyanide.
[16] In 1815 Gay-Lussac deduced Prussic acid's chemical formula.
[17] The radical
cyanide in hydrogen cyanide was given its name from
cyan, not only an English word for a shade of blue but the Greek word for blue (
Ancient Greek:
κυανοῦς), again owing to its derivation from Prussian blue.
Production and synthesis
Hydrogen cyanide forms in at least limited amounts from many
combinations of hydrogen, carbon, and ammonia. Hydrogen cyanide is
currently produced in great quantities by several processes, as well as
being a recovered waste product from the manufacture of
acrylonitrile.
[8] In 2006 between 500 million and 1 billion pounds were produced in the US.
[18]
The most important process is the
Andrussow oxidation invented by
Leonid Andrussow at
IG Farben in which
methane and
ammonia react in the presence of
oxygen at about 1200 °C over a
platinum catalyst:
[19]
- 2 CH4 + 2 NH3 + 3 O2 → 2 HCN + 6 H2O
The energy needed for the reaction is provided by the partial 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:
[20]
- CH4 + NH3 → HCN + 3H2
This reaction is akin to
steam reforming, the reaction of
methane and water to give
carbon monoxide and
hydrogen.
In the Shawinigan Process,
hydrocarbons, e.g.
propane, are reacted with ammonia. 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.
Historical methods of production
The large demand for cyanides for mining operations in the 1890s was met by
George Thomas Beilby, who 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.
Applications
HCN is the precursor to
sodium cyanide and
potassium cyanide, which are used mainly in gold and silver mining and for the electroplating of those metals. Via the intermediacy of
cyanohydrins, a variety of useful organic compounds are prepared from HCN including the
monomer methyl methacrylate, from
acetone, the
amino acid methionine, via the
Strecker synthesis, and the chelating agents
EDTA and
NTA. Via the
hydrocyanation process, HCN is added to
butadiene to give
adiponitrile, a precursor to
Nylon 66.
[8]
Occurrence
HCN is obtainable from
fruits that have a
pit, such as
cherries,
apricots,
apples, and
bitter almonds, from which almond oil and flavoring are made. Many of these pits contain small amounts of
cyanohydrins such as
mandelonitrile and
amygdalin, which slowly release hydrogen cyanide.
[21][22] One hundred grams of crushed apple seeds can yield about 70 mg of HCN.
[23] Some
millipedes release hydrogen cyanide as a defense mechanism,
[24] 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. So-called "bitter" roots of the
cassava plant may contain up to 1 gram of HCN per kilogram.
[25][26]
HCN on the young Earth
It has been postulated that carbon from a cascade of asteroids (known as the
Late Heavy Bombardment),
resulting from interaction of Jupiter and Saturn, blasted the surface
of young Earth and reacted with nitrogen in Earth’s atmosphere to form
HCN.
[27]
HCN in mammals
Some authors have shown that
neurons can produce hydrogen cyanide upon activation of their
opioid receptors by endogenous or exogenous opioids. They have also shown that neuronal production of HCN activates
NMDA receptors and plays a role in
signal transduction between neuronal cells (
neurotransmission). Moreover, increased endogenous neuronal HCN production under opioids was seemingly needed for adequate opioid
analgesia, as analgesic action of opioids was attenuated by HCN scavengers. They considered endogenous HCN to be a neuromodulator.
[28]
It has also been shown that, while stimulating
muscarinic cholinergic receptors in cultured
pheochromocytoma cells
increases HCN production, in a living organism (
in vivo) muscarinic cholinergic stimulation actually
decreases HCN production.
[29]
Leukocytes generate HCN during
phagocytosis, and can kill
bacteria,
fungi, and other pathogens by generating several different toxic chemicals, one of which is hydrogen cyanide.
[28]
The
vasodilatation, caused by
sodium nitroprusside,
has been shown to be mediated not only by NO generation, but also by
endogenous cyanide generation, which adds not only toxicity, but also
some additional antihypertensive efficacy compared to
nitroglycerine and other non-cyanogenic nitrates which do not cause blood cyanide levels to rise.
[30]
HCN and the origin of life
Hydrogen cyanide has been discussed as a precursor to amino acids and
nucleic acids, and is proposed to have played a part in the
origin of life.
[31]
Although the relationship of these chemical reactions to the origin of
life theory remains speculative, studies in this area have led to
discoveries of new pathways to organic compounds derived from the
condensation of HCN.
[32]
HCN in space
HCN has been detected in the
interstellar medium.
[33]
Since then, extensive studies have probed formation and destruction
pathways of HCN in various environments and examined its use as a tracer
for a variety of astronomical species and processes. HCN can be
observed from ground-based
telescopes through a number of
atmospheric windows.
[34] The J=1→0, J=3→2, J= 4→3, and J=10→9 pure
rotational transitions have all been observed.
[33][35][36]
HCN is formed in
interstellar clouds through one of two major pathways:
[37] via a neutral-neutral reaction (CH
2 + N → HCN + H) and via dissociative recombination (HCNH
+ + e
− → HCN + H). The dissociative recombination pathway is dominant by 30%; however, the
HCNH+ must be in its linear form. Dissociative recombination with its structural isomer, H
2NC
+, exclusively produces
hydrogen isocyanide (HNC).
HCN is destroyed in interstellar clouds through a number of mechanisms depending on the location in the cloud.
[37] In
photon-dominated regions (PDRs), photodissociation dominates, producing
CN
(HCN + ν → CN + H). At further depths, photodissociation by cosmic rays
dominate, producing CN (HCN + cr → CN + H). In the dark core, two
competing mechanisms destroy it, forming HCN
+ and HCNH
+ (HCN + H
+ → HCN
+ + H; HCN + HCO
+ → HCNH
+ + CO). The reaction with HCO
+
dominates by a factor of ~3.5. HCN has been used to analyze a variety
of species and processes in the interstellar medium. It has been
suggested as a tracer for dense molecular gas
[38][39] and as a tracer of stellar inflow in high-mass star-forming regions.
[40]
Further, the HNC/HCN ratio has been shown to be an excellent method for
distinguishing between PDRs and X-ray-dominated regions (XDRs).
[41]
On 11 August 2014, astronomers released studies, using the
Atacama Large Millimeter/Submillimeter Array (ALMA) for the first time, that detailed the distribution of HCN,
HNC,
H2CO, and
dust inside the
comae of
comets C/2012 F6 (Lemmon) and
C/2012 S1 (ISON).
[42][43]
As a poison and chemical weapon
A hydrogen cyanide concentration of 300 mg/m
3 in air will kill a human within 10–60 minutes.
[44] A hydrogen cyanide concentration of 3500
ppm (about 3200 mg/m
3) will kill a human in about 1 minute.
[44] The toxicity is caused by the cyanide ion, which halts
cellular respiration by acting as a
non-competitive inhibitor for an enzyme in mitochondria called
cytochrome c oxidase. Specifically CN
− binds to Fe in the
heme subunit in
cytochromes, interrupting electron transfer.
Hydrogen cyanide has been absorbed into a carrier for use as a pesticide. Under IG Farben's brand name
Zyklon B (German >
Cyclone B, with the
B standing for
Blausäure - "Prussic Acid"),
[45] it was used in the
German extermination camps mass killings during
World War II. The same product is currently made in the
Czech Republic under the trademark "Uragan D2". Hydrogen cyanide was also the agent employed in judicial
execution in some
U.S. states, where it was produced during the execution by the action of
sulfuric acid on an egg-sized mass of
potassium cyanide.
[not specific enough to verify]
Hydrogen cyanide is commonly listed amongst
chemical warfare agents known as
blood agents.
[46] 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
Organisation for the Prohibition of Chemical Weapons. During the
First World War, the
United States and
Italy used hydrogen cyanide against the
Central Powers in 1918.
France had used it in combat already in 1916, but this proved to be ineffective due to physical conditions.
[47]
Under the name
prussic acid, HCN has been used as a killing agent in
whaling harpoons.
[48] From the mid 18th century it was used in a number of poisoning murders and suicides.
[49] Cyanide has also been used in major occurrences of suicide in the 20th century, including the deaths of over 900 people at
Jonestown and the
mass suicides in 1945 Nazi Germany.
Hydrogen cyanide gas in air is explosive at concentrations over 5.6%.
[50] This is far above its toxicity level.
References
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