Acetonitrile

Acetonitrile
Skeletal formula of acetonitrile
Skeletal formula of acetonitrile
Skeletal formula of acetonitrile with all explicit hydrogens added
Skeletal formula of acetonitrile with all explicit hydrogens added
Ball and stick model of acetonitrile
Ball and stick model of acetonitrile
Spacefill model of acetonitrile
Spacefill model of acetonitrile
Names
Preferred IUPAC name
Acetonitrile
Systematic IUPAC name
Ethanenitrile
Other names
  • Cyanomethane
  • Ethyl nitrile
  • Methanecarbonitrile
  • Methyl cyanide
  • MeCN
  • ACN
Identifiers
3D model (JSmol)
741857
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.760 Edit this at Wikidata
EC Number
  • 200-835-2
895
MeSH acetonitrile
RTECS number
  • AL7700000
UNII
UN number 1648
  • InChI=1S/C2H3N/c1-2-3/h1H3 checkY
    Key: WEVYAHXRMPXWCK-UHFFFAOYSA-N checkY
  • CC#N
Properties
C2H3N
Molar mass 41.053 g·mol−1
Appearance Colorless liquid
Odor Faint, distinct, fruity
Density 0.786 g/cm3 at 25°C
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·kg)
Acidity (pKa) 25
UV-vismax) 195 nm
Absorbance ≤0.10
−28.0×10−6 cm3/mol
1.344
3.92 D
Thermochemistry
91.69 J/(K·mol)
149.62 J/(K·mol)
40.16–40.96 kJ/mol
−1256.03 – −1256.63 kJ/mol
Hazards
GHS labelling:
GHS02: Flammable GHS07: Exclamation mark
Danger
H225, H302, H312, H319, H332
P210, P280, P305+P351+P338
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
2
3
0
Flash point 2.0 °C (35.6 °F; 275.1 K)
523.0 °C (973.4 °F; 796.1 K)
Explosive limits 4.4–16.0%
Lethal dose or concentration (LD, LC):
  • 2 g/kg (dermal, rabbit)
  • 2.46 g/kg (oral, rat)
5655 ppm (guinea pig, 4 hr)
2828 ppm (rabbit, 4 hr)
53,000 ppm (rat, 30 min)
7500 ppm (rat, 8 hr)
2693 ppm (mouse, 1 hr)
16,000 ppm (dog, 4 hr)
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 40 ppm (70 mg/m3)
REL (Recommended)
TWA 20 ppm (34 mg/m3)
IDLH (Immediate danger)
500 ppm
Related compounds
Related alkanenitriles
Related compounds
DBNPA
Supplementary data page
Acetonitrile (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)
Infobox references

Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula CH3CN and structure H3C−C≡N. 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. The N≡C−C skeleton is linear with a short C≡N distance of 1.16 Å.

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

Applications

Acetonitrile is used mainly as a solvent in the purification of butadiene in refineries. Specifically, acetonitrile is fed into the top of a distillation column filled with hydrocarbons including butadiene, and as the acetonitrile falls down through the column, it absorbs the butadiene which is then sent from the bottom of the tower to a second separating tower. Heat is then employed in the separating tower to separate the butadiene.

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, acetonitrile dissolves a wide range of ionic and nonpolar compounds and is useful as a mobile phase in HPLC and LC–MS.

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 oligonucleotide synthesis from nucleoside phosphoramidites.

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

Organic synthesis

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

As an electron pair donor

Acetonitrile has a free electron pair at the nitrogen atom, which can form many transition metal nitrile complexes. Being weakly basic, it is an easily displaceable ligand. For example, bis(acetonitrile)palladium dichloride is prepared by heating a suspension of palladium chloride in acetonitrile:

PdCl2 + 2 CH3CN → PdCl2(CH3CN)2

A related complex is tetrakis(acetonitrile)copper(I) hexafluorophosphate [Cu(CH3CN)4]+. The CH3CN groups in these complexes are rapidly displaced by many other ligands.

It also forms Lewis adducts with group 13 Lewis acids like boron trifluoride. In superacids, it is possible to protonate acetonitrile.

Production

Acetonitrile is a byproduct 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. 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. In 1992, 14,700 tonnes (16,200 short tons) 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. Due to the global economic slowdown, the production of acrylonitrile used in acrylic fibers and acrylonitrile butadiene styrene (ABS) resins decreased. Acetonitrile is a byproduct in the production of acrylonitrile and its production also decreased, further compounding the acetonitrile shortage. The global shortage of acetonitrile continued through early 2009.[needs update]

Safety

Toxicity

Acetonitrile has only modest toxicity in small doses. It can be metabolised to produce hydrogen cyanide, which is the source of the observed toxic effects. 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).

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. 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.

It has been used in formulations for nail polish remover, despite its toxicity. At least two cases have been reported of accidental poisoning of young children by acetonitrile-based nail polish remover, one of which was fatal. 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.

Metabolism and excretion

Compound Cyanide, concentration in brain (μg/kg) Oral LD50 (mg/kg)
Potassium cyanide 700 ± 200 10
Propionitrile 510 ± 80 40
Butyronitrile 400 ± 100 50
Malononitrile 600 ± 200 60
Acrylonitrile 400 ± 100 90
Acetonitrile 28 ± 5 2460
Table salt (NaCl) 3000
Ionic cyanide concentrations measured in the brains of Sprague-Dawley rats one hour after oral administration of an LD50 of various nitriles.

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 glycolonitrile by an NADPH-dependent cytochrome P450 monooxygenase. The glycolonitrile then undergoes a spontaneous decomposition to give hydrogen cyanide and formaldehyde. 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 120 that for a propionitrile dose 60 times lower (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.

See also


This page was last updated at 2023-10-31 08:58 UTC. Update now. View original page.

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