Acetonitrile

Acetonitrile, also known as cyanomethane, ethanenitrile or methyl cyanide is a organic chemical compound, mainly used as a solvent in chemistry. It has the formula CH₃CN.

Properties

Chemical

Acetonitrile reacts with aldehydes to form hydroxynitriles.

R-CHO + CH₃CN → R-CH(OH)-CH₂(CN)

Palladium chloride will form a complex with acetonitrile:

PdCl₂ + 2 CH₃CN → PdCl₂[CH₃CN]₂

Pyrolysis of acetonitrile yields carbon dioxide, water and hydrogen cyanide.

Physical

Acetonitrile is a colorless liquid, with a faint ether like smell and a sweet burnt smell. Acetonitile is hygroscopic, and will readily absorb water from air if kept in open air over time. It has a melting point between −46 to −44 °C and a boiling point between 81.3 to 82.1 °C.

Availability

Acetonitrile can be purchased from chemical suppliers. ScienceStuff sells 1 liter at $76.88 + UPS hazardous material surcharge of $28.50 per shipment. In most places it's difficult to acquire due to being a cyanide compound.

Preparation

Acetonitrile can be made by dehydrating acetamide, which itself results from the thermal decomposition of ammonium acetate.

CH₃COONH₄ → CH₃C(O)NH₂ + H₂O

CH₃C(O)NH₂ → CH₃CN + H₂O

Projects

• Ethylamine synthesis

Handling

Safety

Acetonitrile has modest toxicity in small doses, but it will be metabolised by the organism to produce hydrogen cyanide, which is very toxic. This occurs several hours after the exposure. Acetonitrile can be absorbed through the skin and via inhalation, so proper protection, such as gloves and a mask should be worn. See cyanide for antidotes and methods of treatment.

Acetonitrile however, has a much lower toxicity than the other simple nitriles, with a LD₅₀ of 2460 mg/kg, while the next simple nitriles (propionitrile, butyronitrile, malononitrile, acrylonitrile) have values between 40-90 mg/kg.

Storage

Acetontrile is very hygroscopic and must be stored in closed bottles. Anhydrous calcium chloride pellets are usually added to keep the solvent dry.

Disposal

Acetonitrile can be neutralized by reacting it with sodium hydroxide, added in excess (for 1 mol MeCN, 2.5 mol NaOH should be added). The byproducts are acetic acid and ammonia.

References

Relevant Sciencemadness threads

• Acetonitrile form Ammonium acetate