Oxidative carbonylation

Oxidative carbonylation is a class of reactions that use carbon monoxide in combination with an oxidant to generate esters and carbonate esters. These transformations utilize transition metal complexes as homogeneous catalysts.[1] Many of these reactions employ palladium catalysts. Mechanistically, these reactions resemble the Wacker process.

Illustrative oxidative carbonylations

Oxidative carbonylation, using palladium-based catalysts, allows certain alkenes to be converted into homologated esters:

2 RCH=CH2 + 2 CO + O2 + 2 MeOH → 2 RCH=CHCO2Me + 2 H2O

Such reactions are assumed to proceed by the insertion of the alkene into the Pd(II)-CO2Me bond of a metallacarboxylic ester followed by beta-hydride elimination (Me = CH3).

Arylboronic acids react with Pd(II) compounds to give Pd(II)-aryl species, which undergo carbonylation to give Pd(II)-C(O)aryl. These benzyl-Pd intermediates are intercepted by alkenes, which insert. Subsequent beta-hydride elimination gives the arylketone.[1]

The conversion of methanol to dimethylcarbonate by oxidative carbonylation is economically competitive with phosgenation. This reaction is practiced commercially using Cu(I) catalysts:[2]

2 CO + O2 + 4 MeOH → 2 (MeO)2CO + 2 H2O

The preparation of dimethyl oxalate by oxidative carbonylation has also attracted commercial interest. It requires only C1 precursors:[3]

4 CO + O2 + 4 MeOH → 2 (MeO2C)2 + 2 H2O

References
  1. Beller, M.; Wu, X.-F. (2013). M. Beller; X.-F. Wu (eds.). Transition Metal Catalyzed Carbonylation Reactions: Carbonylative Activation of C-X Bonds. Berlin, Heidelberg: Springer. doi:10.1007/978-3-642-39016-6_8.
  2. Hans-Josef Buysch. "Carbonic Esters". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a05_197.
  3. Hans-Jürgen Arpe: Industrielle Organische Chemie: Bedeutende Vor- und Zwischenprodukte, S. 168; ISBN 978-3-527-31540-6.
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