Acetonitrile

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Acetonitrile
Skeletal formula of acetonitrile
Skeletal formula of acetonitrile with all explicit hydrogens added
Ball and stick model of acetonitrile
Spacefill model of acetonitrile
Names
IUPAC name
Acetonitrile[2]
Other names
  • Cyanomethane[1]
  • Ethanenitrile[1]
  • Ethyl nitrile[1]
  • Methanecarbonitrile[1]
  • Methyl cyanide[1]
Identifiers
75-05-8 YesY
741857
ChEBI CHEBI:38472 YesY
ChEMBL ChEMBL45211 YesY
ChemSpider 6102 YesY
EC Number 200-835-2
895
Jmol 3D model Interactive image
MeSH acetonitrile
PubChem 6342
RTECS number AL7700000
UNII Z072SB282N YesY
UN number 1648
  • InChI=1S/C2H3N/c1-2-3/h1H3 YesY
    Key: WEVYAHXRMPXWCK-UHFFFAOYSA-N YesY
  • CC#N
Properties
C2H3N
Molar mass 41.05 g·mol−1
Appearance Colorless liquid
Density 0.786 g mL−1
Melting point −46 to −44 °C; −51 to −47 °F; 227 to 229 K
Boiling point 81.3 to 82.1 °C; 178.2 to 179.7 °F; 354.4 to 355.2 K
Miscible
log P −0.334
Vapor pressure 9.71 kPa (at 20.0 °C)
530 μmol Pa−1 kg−1
Acidity (pKa) 25
Basicity (pKb) −11
UV-vis (λmax) 195 nm
Absorbance ≤0.10
1.344
Thermochemistry
91.69 J K−1 mol−1
149.62 J K−1 mol−1
40.16–40.96 kJ mol−1
−1256.03–−1256.63 kJ mol−1
Vapor pressure {{{value}}}
Related compounds
Related alkanenitriles
Related compounds
 DBNPA
Supplementary data page
Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
 Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
YesY verify (what is YesYN ?)
Infobox references

Acetonitrile is the chemical compound with the formula CH
3CN. This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not classed as organic). It is produced mainly as a byproduct of acrylonitrile manufacture. It is used as a polar aprotic solvent in organic synthesis and in the purification of butadiene.[3]

In the laboratory, it is used as a medium-polarity solvent that is miscible with water and a range of organic solvents, but not saturated hydrocarbons. It has a convenient liquid range and a high dielectric constant of 38.8. With a dipole moment of 3.92 D,[4] acetonitrile dissolves a wide range of ionic and nonpolar compounds and is useful as a mobile phase in HPLC and LC-MS. The N-C-C skeleton is linear with a short C-N distance of 1.16 Å.[5]

Acetonitrile was first prepared in 1847 by the French chemist Jean-Baptiste Dumas.[6]

Applications

Acetonitrile is used mainly as a solvent in the purification of butadiene in refineries.

It is widely used in battery applications because of its relatively high dielectric constant and ability to dissolve electrolytes. For similar reasons it is a popular solvent in cyclic voltammetry.

Its ultraviolet transparency UV cutoff, low viscosity and low chemical reactivity make it a popular choice for high-performance liquid chromatography (HPLC).

Acetonitrile plays a significant role as the dominant solvent used in the manufacture of DNA oligonucleotides from monomers.

Industrially, it is used as a solvent for the manufacture of pharmaceuticals and photographic film.[7]

Organic synthesis

Acetonitrile is a common two-carbon building block in organic synthesis[8] of many useful chemicals, including acetamidine hydrochloride, thiamine, and α-napthaleneacetic acid.[9] Its reaction with cyanogen chloride affords malononitrile.[3]

Ligand in coordination chemistry

In inorganic chemistry, acetonitrile is employed as a solvent and often an easily displaceable ligand. For example, PdCl
2(CH
3CN)
2 is prepared by heating a suspension of (polymeric) palladium chloride in acetonitrile:[citation needed]

PdCl
2 + 2 CH
3CN → PdCl
2(CH
3CN)
2

A related complex is [Cu(MeCN)4]+. The CH
3CN groups in these complexes are rapidly displaced by many other ligands.

Production

Methyl cyanide has been detected in the protoplanetary disc surrounding a young star.[10]

Acetonitrile is a by-product from the manufacture of acrylonitrile. Most is combusted to support the intended process but an estimated several thousand tons are retained for the above-mentioned applications.[11] 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.[12] In 1992, 32.3 million pounds (14,700 t) of acetonitrile were produced in the US.

Acetonitrile shortage in 2008–2009

Starting in October 2008, the worldwide supply of acetonitrile was low because Chinese production was shut down for the Olympics. Furthermore, a U.S. factory was damaged in Texas during Hurricane Ike.[13] Due to the global economic slowdown, the production of acrylonitrile that is used in acrylic fibers and acrylonitrile-butadiene-styrene (ABS) resins decreased. Because acetonitrile is a byproduct in the production of acrylonitrile, its production has also decreased.[14] The global shortage of acetonitrile continued through early 2009.

Safety

Toxicity

Acetonitrile has only a modest toxicity in small doses.[9][15] It can be metabolised to produce hydrogen cyanide, which is the source of the observed toxic effects.[7][16][17] Generally the onset of toxic effects is delayed, due to the time required for the body to metabolize acetonitrile to cyanide (generally about 2–12 hours).[9]

Cases of acetonitrile poisoning in humans (or, to be more specific, of cyanide poisoning after exposure to acetonitrile) are rare but not unknown, by inhalation, ingestion and (possibly) by skin absorption.[16] 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 emergency treatments.[16]

It has been used in formulations for nail polish remover, despite its low but significant toxicity.[18] 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.[19]

Metabolism and excretion

Compound Brain cyanide concentration (µg/kg) Oral LD50 (mg/kg)
Acetonitrile 28±5 2460
Propionitrile 508±84 40
Butyronitrile 437±106 50
Malononitrile 649±209 60
Acrylonitrile 395±106 90
Potassium cyanide 748±200 10
Ionic cyanide concentrations measured in the brains of Sprague-Dawley rats one hour after oral administration of an LD50 of various nitriles.[20]

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.[21] The first step in this pathway is the oxidation of acetonitrile to glycolonitrile by an NADPH-dependent cytochrome P450 monooxygenase. The glycolonitrile then undergoes a spontaneous decomposition to give hydrogen cyanide and formaldehyde.[15][16] Formaldehyde, a toxin and a carcinogen on its own, is further oxidized to formic acid, which is another source of toxicity.

The metabolism of acetonitrile is much slower than that of other nitriles, which accounts for its relatively low toxicity. Hence, one hour after administration of a potentially lethal dose, the concentration of cyanide in the rat brain was one-twentieth that for a propionitrile dose 60 times lower (see table).[20]

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.[15][16][17]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ 3.0 3.1 [1], Ashford's Dictionary of Industrial Chemicals, Third edition, 2011, page 76.
  4. ↑ Steiner, P. A., and Gordy, W., 1966, J. molec. Spectrosc., 21, 291.
  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ 7.0 7.1 Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ Lua error in package.lua at line 80: module 'strict' not found.; Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ 9.0 9.1 9.2 Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ US 4179462, Olive, G. & Olive, S., "Process for preparing acetonitrile", published 1979-12-18, assigned to Monsanto Company 
  13. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ 15.0 15.1 15.2 Lua error in package.lua at line 80: module 'strict' not found.
  16. ↑ 16.0 16.1 16.2 16.3 16.4 Lua error in package.lua at line 80: module 'strict' not found.
  17. ↑ 17.0 17.1 Lua error in package.lua at line 80: module 'strict' not found.
  18. ↑ At least two cases have been reported of accidental poisoning of young children by acetonitrile-based nail polish remover, one of which was fatal: Lua error in package.lua at line 80: module 'strict' not found.
  19. ↑ Twenty-Fifth Commission Directive 2000/11/EC of 10 March 2000 adapting to technical progress Annex II to Council Directive 76/768/EEC on the approximation of laws of the Member States relating to cosmetic products. OJEC L65 of 2000-03-14, pp. 22–25.
  20. ↑ 20.0 20.1 Lua error in package.lua at line 80: module 'strict' not found.
  21. ↑ Lua error in package.lua at line 80: module 'strict' not found.

External links

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