Ammoxidation

In chemistry, ammoxidation is an industrial process for the production of nitriles using ammonia and oxygen. The usual substrates are alkenes. It is sometimes called the Sohio process, acknowledging that ammoxidation was commercialized by Standard Oil of Ohio. An important application of this process is the production of acrylonitrile:^[1]

CH₃CH=CH₂ + 3/2 O₂ + NH₃ → NCCH=CH₂ + 3 H₂O

Several million tons of acrylonitrile are produced in this way annually. The world's supply of the solvent acetonitrile is a byproduct of this particular process.

Scope

Ammoxidation of alkenes exploits the weak C-H bonds that are located in the allylic position of unsaturated hydrocarbons. Benzylic C-H bonds are also susceptible to ammoxidation, reflecting the weakness of their C-H bonds. For this reason, cyanopyridines (e.g. the precursor to niacin) and benzonitriles are produced from methylpyridines and toluene, respectively. Dinitriles are produced by double ammoxidation, examples being phthalonitriles (precursor to phthalocyanines) and terephthalonitriles, both from xylenes.

Typical catalysts are the oxides of vanadium and molybdenum. π-Allyl complexes are assumed as intermediates.^[2]

Related processes

Instead of alkenes, alcohols and aldehydes are competent substrates:

O=CHCH=CH₂ + 1/2 O₂ + NH₃ → NCCH=CH₂ + 2 H₂O

HOCH₂CH=CH₂ + O₂ + NH₃ → NCCH=CH₂ + 3 H₂O

These substrates are usually more expensive than the alkenes, so they are less common.

Hydrogen cyanide is prepared by an ammoxidation-like reaction of methane, the Andrussov oxidation:

CH₄ + NH₃ + 3/2 O₂ → HCN + 3 H₂O

References

1. ^ Peter Pollak, Gérard Romeder, Ferdinand Hagedorn, Heinz-Peter Gelbke "Nitriles" Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a17_363
2. ^ Nugent, W. A.; Mayer, J. M., Metal-Ligand Multiple Bonds. J. Wiley: New York, 1988.