Acetonitrile - High Dielectric Constant 38.8, Polar Aprotic Solvent For Organic Synthesis And Purification

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.[5]

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,[6] acetonitrile dissolves a wide range of ionic and nonpolar compounds and is useful as a mobile phase in HPLC and LCa MS. The Na Ca C skeleton is linear with a short Ca N distance of 1.16 A .[7]

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.

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.[9]

Organic synthesis
Acetonitrile is a common two-carbon building block in organic synthesis[10] of many useful chemicals, including acetamidine hydrochloride, thiamine, and I -napthaleneacetic acid.[11] Its reaction with cyanogen chloride affords malononitrile.[5]

Ligand in coordination chemistry
Acetonitrile is a ligand in 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:[12]

PdCl
2 + 2 CH
3CN a PdCl
2(CH
3CN)
2
A related complex is [Cu(CH3CN)4]+. The CH
3CN groups in these complexes are rapidly displaced by many other ligands.

Safety
Toxicity
Acetonitrile has only modest toxicity in small doses.[11][18] It can be metabolised to produce hydrogen cyanide, which is the source of the observed toxic effects.[9][19][20] Generally the onset of toxic effects is delayed, due to the time required for the body to metabolize acetonitrile to cyanide (generally about 2a 12 hours).[11]

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.[19] 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.[19]

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.[21] Acetone and ethyl acetate are often preferred as safer for domestic use, and acetonitrile has been banned in cosmetic products in the European Economic Ar