Carbonylation

Carbonylation refers to the process by which a reaction introduces carbon monoxide into organic substrates. Several chemicals used significantly in industry are prepared by carbonylation because carbon monoxide is inexpensive, and its reactivity can be highly selective. Carbonylations produce organic carbonyls, i.e., compounds that contain the C=O functional group.^[1][2] Carbonylations are the basis of two main types of reactions, hydroformylation and Reppe Chemistry.

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Hydroformylation

Hydroformylation entails the addition of both carbon monoxide and hydrogen to unsaturated organic compounds, usually alkenes. The usual products are aldehydes:

RCH=CH₂ + H₂ + CO → RCH₂CH₂CHO

The reaction requires metal catalysts that activate the CO via formation of metal carbonyls.

Reppe Chemistry

Reppe Chemistry, named after Walter Reppe, entails addition of carbon monoxide and an acidic hydrogen donor to the organic substrate. The largest-scale application of this type of carbonylation is the Monsanto acetic acid process, which produces acetic acid from methanol. In the related hydrocarboxylation and hydroesterification, alkenes and alkynes are the substrates. This method is used in industry to produce propionic acid from ethylene:

RCH=CH₂ + H₂O + CO → CH₃CH₂CO₂H

These reactions require metal catalysts, which bind and activate the CO. In the industrial synthesis of Ibuprofin, a benzylic alcohol is converted to the corresponding carboxylic acid via a Pd-catalyzed carbonylation:^[1]

ArCH(CH₃)OH + CO → ArCH(CH₃)CO₂H

Acrylic acid was once prepared by the hydrocarboxylation of acetylene, but is now produced by the oxidation of propene.

Other reactions

The Koch reaction (also the related Koch-Haaf reactions) entail the addition of CO to unsaturated compounds in the presence of strong acids such as sulfuric acid. This method is not as frequently used in industry as are the metal-catalyzed reactions, described above. The conversion of isobutene to pivalic acid is illustrative of the process:

(CH₃)₂C=CH₂ + H₂O + CO → (CH₃)₃CCO₂H

Unrelated to the Koch reaction, dimethylcarbonate and dimethyloxalate are also produced in industry from carbon monoxide.^[1] These reactions require oxidants:

2 CH₃OH + 1/2 O₂ + CO → (CH₃O)₂CO + H₂O

References

1. ^ ^{a b c} W. Bertleff, M. Roeper, X. Sava, “Carbonylation” in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH: Weinheim, 2003. DOI: 10.1002/14356007.a05 217.
2. ^ Arpe, .J.: Industrielle organische Chemie: Bedeutende vor- und Zwischenprodukte, 2007, Wiley-VCH-Verlag, ISBN 3527315403