Carbonylation

Carbonylation

[kahr-bon-l-eyt]
Carbonylation refers to reactions that introduce carbon monoxide into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry.

Organic chemistry

Several chemicals used significantly in industry are prepared by carbonylation, which can be highly selective reactions. Carbonylations produce organic carbonyls, i.e., compounds that contain the C=O functional group. Carbonylations are the basis of two main types of reactions, hydroformylation and Reppe Chemistry.

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 binds the CO, the H2, and the alkene, allowing these substrates to combine within its coordination sphere.

Reppe Chemistry

Reppe Chemistry, named after Walter Reppe, entails addition of carbon monoxide and an acidic hydrogen donor to the organic substrate. Large-scale applications of this type of carbonylation are the Monsanto and Cativa processes, which convert methanol to acetic acid. Acetic anhydride is prepared by a related carbonylation of methyl acetate.. 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:
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 less frequently used in industry as are the metal-catalyzed reactions, described above. The industrial synthesis of glycolic acid is achieved in this way:
CH2O + CO + H2O → HOCH2CO2H
The conversion of isobutene to pivalic acid is also illustrative:
(CH3)2C=CH2 + H2O + CO → (CH3)3CCO2H

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

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

Inorganic chemistry

Metal carbonyls, compounds with the formula M(CO)xLy (M = metal; L = other ligands) are prepared by carbonylation of transition metals. Iron and nickel powder react directly with CO to give Fe(CO)5 and Ni(CO)4, respectively. Most other metals form carbonyls less directly, such as from their oxides or halides. Metal carbonyls wildly employed as catalysts in the hydroformylation and Reppe processes discussed above.

References

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