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Acetonitrile, often abbreviated MeCN (methyl cyanide), is the
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with the formula and
structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such a ...
. This colourless liquid is the simplest organic nitrile ( hydrogen cyanide is a simpler nitrile, but the
cyanide Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms. In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...
anion is not classed as
organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...
). It is produced mainly as a byproduct of
acrylonitrile Acrylonitrile is an organic compound with the formula and the structure . It is a colorless, volatile liquid although commercial samples can be yellow due to impurities. It has a pungent odor of garlic or onions. In terms of its molecula ...
manufacture. It is used as a polar aprotic solvent in organic synthesis and in the purification of
butadiene 1,3-Butadiene () is the organic compound with the formula (CH2=CH)2. It is a colorless gas that is easily condensed to a liquid. It is important industrially as a precursor to synthetic rubber. The molecule can be viewed as the union of two v ...
. The skeleton is
linear Linearity is the property of a mathematical relationship ('' function'') that can be graphically represented as a straight line. Linearity is closely related to '' proportionality''. Examples in physics include rectilinear motion, the linear ...
with a short
distance Distance is a numerical or occasionally qualitative measurement of how far apart objects or points are. In physics or everyday usage, distance may refer to a physical length or an estimation based on other criteria (e.g. "two counties over"). ...
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 1,3-Butadiene () is the organic compound with the formula (CH2=CH)2. It is a colorless gas that is easily condensed to a liquid. It is important industrially as a precursor to synthetic rubber. The molecule can be viewed as the union of two v ...
in refineries. Specifically, acetonitrile is fed into the top of a
distillation column A fractionating column or fractional column is an essential item used in the distillation of liquid mixtures to separate the mixture into its component parts, or fractions, based on the differences in volatilities. Fractionating columns are used in ...
filled with
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
s 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 The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insula ...
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 Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...
applications because of its relatively high
dielectric constant The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insula ...
and ability to dissolve electrolytes. For similar reasons it is a popular solvent in
cyclic voltammetry Cyclic voltammetry (CV) is a type of potentiodynamic electrochemical measurement. In a cyclic voltammetry experiment, the working electrode potential is ramped linearly versus time. Unlike in linear sweep voltammetry, after the set potential is r ...
. Its ultraviolet transparency UV cutoff, low
viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the int ...
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
monomer In chemistry, a monomer ( ; '' mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization. Classification ...
s. Industrially, it is used as a solvent for the manufacture of
pharmaceutical A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the medical field and ...
s 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 In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elect ...
. For example,
bis(acetonitrile)palladium dichloride Bis(acetonitrile)palladium dichloride is the coordination complex with the formula PdCl2(NCCH3)2. It is the adduct of two acetonitrile ligands with palladium(II) chloride. It is a yellow-brown solid that is soluble in organic solvents. The com ...
is prepared by heating a suspension of
palladium chloride Palladium(II) chloride, also known as palladium dichloride and palladous chloride, are the chemical compounds with the formula PdCl2. PdCl2 is a common starting material in palladium chemistry – palladium-based catalysts are of particular value ...
in acetonitrile: :PdCl2 + 2 CH3CN -> PdCl2(CH3CN)2 A related complex is
tetrakis(acetonitrile)copper(I) hexafluorophosphate Tetrakis(acetonitrile)copper(I) hexafluorophosphate is a salt with the formula u(CH3CN)4F6. It is a colourless solid that is used in the synthesis of other copper complexes. The cation u(CH3CN)4sup>+ is a well-known example of a transition meta ...
. The 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 Acrylonitrile is an organic compound with the formula and the structure . It is a colorless, volatile liquid although commercial samples can be yellow due to impurities. It has a pungent odor of garlic or onions. In terms of its molecula ...
. 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 Acrylonitrile is an organic compound with the formula and the structure . It is a colorless, volatile liquid although commercial samples can be yellow due to impurities. It has a pungent odor of garlic or onions. In terms of its molecula ...
. 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 Acetamide (systematic name: ethanamide) is an organic compound with the formula CH3CONH2. It is the simplest amide derived from acetic acid. It finds some use as a plasticizer and as an industrial solvent. The related compound ''N'',''N''-dime ...
or by
hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic ...
of mixtures of
carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...
and
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
. In , of acetonitrile were produced in the US. Catalytic ammoxidation of
ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene ...
was also researched.


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 The modern Olympic Games or Olympics (french: link=no, Jeux olympiques) are the leading international sporting events featuring summer and winter sports competitions in which thousands of athletes from around the world participate in a vari ...
. Furthermore, an U.S. factory was damaged in Texas during
Hurricane Ike Hurricane Ike () was a powerful tropical cyclone that swept through portions of the Greater Antilles and Northern America in September 2008, wreaking havoc on infrastructure and agriculture, particularly in Cuba and Texas. Ike took a sim ...
. 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 Acrylonitrile is an organic compound with the formula and the structure . It is a colorless, volatile liquid although commercial samples can be yellow due to impurities. It has a pungent odor of garlic or onions. In terms of its molecula ...
and its production also decreased, further compounding the acetonitrile shortage. The global shortage of acetonitrile continued through early 2009.


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 Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of th ...
, and vomiting. Convulsions and coma can occur in serious cases, followed by death from respiratory failure. The treatment is as for
cyanide poisoning Cyanide poisoning is poisoning that results from exposure to any of a number of forms of cyanide. Early symptoms include headache, dizziness, fast heart rate, shortness of breath, and vomiting. This phase may then be followed by seizures, ...
, with
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
,
sodium nitrite Sodium nitrite is an inorganic compound with the chemical formula NaNO2. It is a white to slightly yellowish crystalline powder that is very soluble in water and is hygroscopic. From an industrial perspective, it is the most important nitrite ...
, and
sodium thiosulfate Sodium thiosulfate (sodium thiosulphate) is an inorganic compound with the formula . Typically it is available as the white or colorless pentahydrate, . The solid is an efflorescent (loses water readily) crystalline substance that dissolves well ...
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 Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscibl ...
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

In common with other nitriles, acetonitrile can be metabolised in
microsome In cell biology, microsomes are heterogeneous vesicle-like artifacts (~20-200 nm diameter) re-formed from pieces of the endoplasmic reticulum (ER) when eukaryotic cells are broken-up in the laboratory; microsomes are not present in healthy, li ...
s, 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 Cytochromes P450 (CYPs) are a superfamily of enzymes containing heme as a cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are important for the clearance of various co ...
monooxygenase Monooxygenases are enzymes that incorporate one hydroxyl group (−OH) into substrates in many metabolic pathways. In this reaction, the two atoms of dioxygen are reduced to one hydroxyl group and one H2O molecule by the concomitant oxidation o ...
. The glycolonitrile then undergoes a spontaneous decomposition to give hydrogen cyanide and
formaldehyde Formaldehyde ( , ) ( systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section ...
. 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 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

* Trichloroacetonitrile – a derivative of acetonitrile used to protect alcohol groups, and also used as a reagent in the Overman rearrangement


References


External links


WebBook page for C2H3N







Chemical Summary for Acetonitrile (CAS No. 75-05-8)
Office of Pollution Prevention and Toxics, U.S. Environmental Protection Agency
Simulation of acetonitrile

How Did Organic Matter Reach Earth? Cosmic Detectives Trace Origin of Complex Organic Molecules
on: SciTechDaily. September 10, 2020. Source: Tokyo University of Science: Acetonitrile found in molecular cloud Sgr B2(M) at the center of our galaxy. {{Authority control Hazardous air pollutants 2 Solvents Ligands Organic compounds with 2 carbon atoms