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Acetonitrile
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Acetonitrile (ACN) is the chemical compound with formula CH3CN. This colourless liquid is the simplest organic nitrile and is widely used as a solvent.
onitrile is a by-product from the manufacture of acrylonitrile. Production trends for acetonitrile thus generally follow those of acrylonitrile. Acetonitrile can also be produced by many other methods, but these are of no commercial importance as of 2002.
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Acetonitrile (ACN) is the chemical compound with formula CH3CN. This colourless liquid is the simplest organic nitrile and is widely used as a solvent.
Production
Acetonitrile is a by-product from the manufacture of acrylonitrile. Production trends for acetonitrile thus generally follow those of acrylonitrile. Acetonitrile can also be produced by many other methods, but these are of no commercial importance as of 2002. Illustrative routes are by dehydration of acetamide or by hydrogenation of mixtures of carbon monoxide and ammonia. The four main producers of acetonitrile in the United States are: INEOS, DuPont, J.T. Baker Chemical, and Sterling Chemicals. In , 32.3 million pounds (14,700 t) of acetonitrile were produced in the US.
As of October 2008, there is a world wide shortage of acetonitrile. The shortage results from an attenuated output from China as production was shut down for the Olympics as well as damage to a U.S. factory in Texas during Hurricane Ike. Due to the global economic slowdown, the production of acrylonitrile which is used in acrylic fibers and acrylonitrile-butadiene (ABS) resins has also decreased (used to make plastic moldings from car parts to Lego bricks). Because acetonitrile is a byproduct in the production of acrylonitrile, its production has also decreased.
Applications
Solvent
Acetonitrile is a polar solvent, with a dipole moment of 3.84 D, miscible with water and with a convenient liquid range. It has been used in formulations for nail polish remover, despite its low but significant toxicity. Acetone and ethyl acetate are often preferred as safer for domestic use, and acetonitrile has been banned in cosmetic products in the European Economic Area since March 2000.
Acetonitrile dissolves a wide range of compounds without complications, due to its low acidity. Its low viscosity and low chemical reactivity make it a popular choice for liquid chromatography. Similarly, it is a popular solvent in cyclic voltammetry because of its relatively high dielectric constant. Industrially, it is used as a solvent in the purification of butadiene and in the manufacture of pharmaceuticals and photographic film.
Organic synthesis
Acetonitrile is a two-carbon building block in organic synthesis as in the production of pesticides to perfumes. Its reaction with cyanogen chloride affords malononitrile.
Ligand in inorganic chemistry
In inorganic chemistry, acetonitrile is employed as a displaceable ligand. For example, PdCl2(CH3CN)2 is prepared by heating a suspension of (polymeric) palladium chloride in acetonitrile:
- PdCl2 + 2 CH3CN ? PdCl2(CH3CN)2
Safety
Toxicity
Acetonitrile itself has only a modest toxicity, but it can be metabolised to produce hydrogen cyanide (see below), which is the source of the observed toxic effects. Cases of acetonitrile poisoning in humans (or, more strictly, of cyanide poisoning after exposure to acetonitrile) are rare but not unknown, by inhalation, ingestion and (possibly) by skin absorption. The symptoms, which do not usually appear for several hours after the exposure, include breathing difficulties, slow pulse rate, nausea and vomiting: convulsions and coma can occur in serious cases, followed by death from respiratory failure. The treatment is as for cyanide poisoning, with oxygen, sodium nitrite and sodium thiosulfate among the most commonly used remedies.
Metabolism and excretion
In common with other nitriles, acetonitrile can be metabolised in microsomes, especially in the liver, to produce hydrogen cyanide, as was first shown by Pozzani et al. in 1959. The first step in this pathway is the oxidation of acetonitrile to glyconitrile by an NADPH-dependent cytochrome P450 monooxygenase. The glyconitrile then undergoes a spontaneous decondensation to give hydrogen cyanide and formaldehyde.
The metabolism of acetonitrile is much slower than that of other nitriles, which accounts for its relatively low toxicity. Hence, one hour after receiving a potentially lethal dose, the concentration of cyanide in the brain is 20-times lower for acetonitrile poisoning than for propionitrile poisoning, despite the fact that the administered dose was 60-times higher (see table).
The relatively slow metabolism of acetonitrile to hydrogen cyanide allows more of the cyanide produced to be detoxified within the body to thiocyanate (the rhodanese pathway). It also allows more of the acetonitrile to be excreted unchanged before it is metabolised. The main pathways of excretion are by exhalation and in the urine.
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