Oxidative carbonylation is a class of reactions that use
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
in combination with an oxidant to generate
ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...
s and
carbonate ester
In organic chemistry, a carbonate ester (organic carbonate or organocarbonate) is an ester of carbonic acid. This functional group consists of a carbonyl group flanked by two alkoxy groups. The general structure of these carbonates is and they ...
s. These transformations utilize transition metal complexes as
homogeneous catalyst
In chemistry, homogeneous catalysis is catalysis by a soluble catalyst in a solution. Homogeneous catalysis refers to reactions where the catalyst is in the same phase as the reactants, principally in solution. In contrast, heterogeneous catalysis ...
s.
Many of these reactions employ palladium catalysts. Mechanistically, these reactions resemble the
Wacker process
The Wacker process or the Hoechst-Wacker process (named after the chemical companies of the same name) refers to the oxidation of ethylene to acetaldehyde in the presence of palladium(II) chloride as the catalyst. This chemical reaction was one of ...
.
Illustrative oxidative carbonylations
Oxidative carbonylation, using palladium-based catalysts, allows certain alkenes to be converted into homologated esters:
:2 RCH=CH
2 + 2 CO + O
2 + 2 MeOH → 2 RCH=CHCO
2Me + 2 H
2O
Such reactions are assumed to proceed by the insertion of the alkene into the Pd(II)-CO
2Me bond of a
metallacarboxylic ester A metallacarboxylic acid is a metal complex with the ligand CO2H. These compounds are intermediates in reactions that involve carbon monoxide and carbon dioxide, these species are intermediates in the water gas shift reaction. Metallacarboxylic acid ...
followed by
beta-hydride elimination
β-Hydride elimination is a reaction in which an alkyl group bonded to a metal centre is converted into the corresponding metal-bonded hydride and an alkene. The alkyl must have hydrogens on the β-carbon. For instance butyl groups can undergo th ...
(Me = CH
3).
Arylboronic acid
Phenylboronic acid or benzeneboronic acid, abbreviated as PhB(OH)2 where Ph is the phenyl group C6H5-, is a boronic acid containing a phenyl substituent and two hydroxyl groups attached to boron. Phenylboronic acid is a white powder and is comm ...
s 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.
[
The conversion of methanol to dimethylcarbonate by oxidative carbonylation is economically competitive with ]phosgenation
Phosgene is the organic chemical compound with the formula COCl2. It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. Phosgene is a valued and important industrial building block, espe ...
. This reaction is practiced commercially using Cu(I) catalysts:dimethyl oxalate
Dimethyl oxalate is the organic compound with the formula (CO2CH3)2. It is the dimethyl ester of oxalic acid. Dimethyl oxalate is a colorless or white solid that is soluble in water.
Production
Dimethyl oxalate can be obtained by esterification ...
by oxidative carbonylation has also attracted commercial interest. It requires only C1 precursors:[Hans-Jürgen Arpe: ''Industrielle Organische Chemie: Bedeutende Vor- und Zwischenprodukte'', S. 168; {{ISBN, 978-3-527-31540-6.]
:4 CO + O2 + 4 MeOH → 2 (MeO2C)2 + 2 H2O
References
Chemical reactions
Carbon monoxide