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 first discovered by Standard Oil of Ohio in 1957.[1][2] An important application of this process is the production of acrylonitrile:[3]

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

Several million tons of acrylonitrile are produced in this way annually. The solvent acetonitrile is a byproduct of this process.[4]

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. 3-cyanopyridine, 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.[5]

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

See also

References
  1. Callahan, James L.; Grasselli, Robert K.; Milberger, Ernest C.; Strecker, H. Arthur (1 June 1970). "Oxidation and Ammoxidation of Propylene over Bismuth Molybdate Catalyst". Industrial & Engineering Chemistry Product Research and Development. 9 (2): 134–142. doi:10.1021/i360034a003.
  2. "Sohio Acrylonitrile Process - American Chemical Society". American Chemical Society. Retrieved 11 July 2017.
  3. 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
  4. "The Sohio Acrylonitrile Process". National Historic Chemical Landmarks. American Chemical Society. Archived from the original on February 23, 2013. Retrieved March 25, 2013.
  5. Nugent, W. A.; Mayer, J. M., Metal-Ligand Multiple Bonds. J. Wiley: New York, 1988.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.