|The reaction for carbon dioxide splitting into carbon monoxide with aromatic aldehydes as oxygen acceptors. Credit: ACS, Gu and Zhang. Click to enlarge.|
A team of researchers in Singapore have developed a process for the catalytic reduction of carbon dioxide (CO2) to carbon monoxide (CO) under mild conditions, using aromatic aldehydes as reductants and N-Heterocyclic Carbenes (NHCs) as organocatalysts.
The resulting CO can be used to convert water to hydrogen via the water gas shift reaction. The reaction also shows a new economical way to oxidize aromatic aldehydes, and could be applied in pharmaceutical synthesis. A paper on the work was published online 29 December in the Journal of the American Chemical Society.
There is increasing attention being focused on the conversion and utilization of CO2 for the production of fuels and chemicals; the 238th American Chemical Society (ACS) national meeting in August featured a day-long symposium on advances in the area. (Earlier post.)
Carbon dioxide, however, is highly stable, and splitting the O=C(O) bond to generate carbon monoxide requires large energy input. Authors Liuqun Gu and Yugen Zhang from the Institute of Bioengineering and Nanotechnology note that there are currently four basic categories of carbon dioxide splitting methods:
- Enzyme carbon monoxide dehydrogenase/ acetyl-CoA synthase (CODH/ACS);
- Electrochemical reduction; and
- Use of metal complexes or metal oxides to abstract the oxygen from carbon dioxide to form carbon monoxide in low turnover.
...reduction of carbon dioxide with organocatalysts remained widely undeveloped until our group reported the first hydrosilylation of carbon dioxide using NHC catalyst under mild conditions recently. In our efforts to look for cheaper and more accessible reductants for CO2 reduction, the new reaction for carbon dioxide splitting into carbon monoxide with aromatic aldehydes as oxygen acceptors was successfully developed. To our best knowledge, this is the first case in the reduction of carbon dioxide to form carbon monoxide using organocatalysts.
—Gu and Zhang
The calculated free energy profile showed that the overall reaction is an exothermic process with a small negative energy difference of ΔE= -7.0 kcal/mol.
Liuqun Gu and Yugen Zhang (2009) Unexpected CO2 Splitting Reactions To Form CO with N-Heterocyclic Carbenes as Organocatalysts and Aromatic Aldehydes as Oxygen Acceptors. J. Am. Chem. Soc., Article ASAP doi: 10.1021/ja909038t