Acetonitrile

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Acetonitrile
Acetonitrile bottle and sample.jpg
Acetonitrile sample and its original bottle.
Names
IUPAC name
Acetonitrile
Systematic IUPAC name
Acetonitrile
Other names
Cyanomethane
Ethanenitrile
Ethyl nitrile
Methanecarbonitrile
Methyl cyanide
Identifiers
Jmol-3D images Image
Properties
C2H3N
CH3CN
Molar mass 41.05 g/mol
Appearance Colorless liquid
Odor Faint, ethereal
Density 0.786 g/mL
Melting point −46 to −44 °C (−51 to −47 °F; 227 to 229 K)
Boiling point 81.3 to 82.1 °C (178.3 to 179.8 °F; 354.4 to 355.2 K)
Miscible
Solubility Miscible with acetone, ethanol, methyl ethyl ketone, toluene, xylene
Vapor pressure 9.71 kPa (at 20.0 °C)
Thermochemistry
149.62 J·K−1·mol−1
40.16–40.96 kJ·mol−1
Hazards
Safety data sheet ScienceLab
Flash point 2.0 °C
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)
Related compounds
Related compounds
Hydrogen cyanide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

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)[1]

Palladium chloride will form a complex with acetonitrile:

PdCl2 + 2 CH3CN → PdCl2[CH3CN]2

Pyrolysis of acetonitrile yields primarily methane and hydrogen cyanide.

Acetonitrile burns in air with a gray-pinkish flame.

Physical

Acetonitrile is a colorless liquid, with a faint ether-like or sweet-burnt smell. It is miscible with a variety of organic solvents, but immiscible with saturated hydrocarbons. 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

Phosphorus pentoxide is is widely used as catalyst. Other dehydrating agents include titanium(IV) chloride, thionyl chloride and trifluoroacetic anhydride. Dehydration is know to produce lots of side products, which form a hard to remove goo.

The book Catalysis in organic chemistry by P. Sabatier (see Library below) mentions several authors which claim that it's possible to obtain acetonitrile by dehydrating acetamide, via refluxing at 250-260 °C, for 4 hours, using readily available materials as catalyst.[2]

Catalyst Alumina Lamp black Pumice Powdered glass Sand Horse teeth
Yield (%) 68 68 65 65 52 35

By carrying the amide in a current of air over the catalyst heated to 420 °C, the yields are improved:[3]

Catalyst Pumice Sand Alumina Graphite
Yield (%) 91.5 86.5 82 75.5

Aqueous palladium(II) chloride can convert primary amides into nitriles, in a water-acetonitrile 1:1 mixture, the conversion takes place at room temperature over the course of several hours.[4]

Heating methylurea with ammonium sulfamate will yield acetonitrile.[5]

Projects

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 2,460 mg/kg, while the next primary nitriles (propionitrile, butyronitrile, malononitrile, acrylonitrile) have LD50 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.[6]

References

  1. http://onlinelibrary.wiley.com/doi/10.1002/anie.201302613/abstract
  2. http://pubs.acs.org/doi/10.1021/ja02268a025
  3. http://pubs.acs.org/doi/10.1021/ja02268a026
  4. http://pubs.acs.org/doi/abs/10.1021/ol052100l
  5. http://www.nrcresearchpress.com/doi/pdf/10.1139/v56-214
  6. http://link.springer.com/article/10.1007%2FBF02318626

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