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Loose grip

January 28, 1999

Carbon dioxide (CO2) is contained in the air we exhale, and is also always formed when carbon-containing substances such as oil, gas, wood, and plastics are burned - it is omnipres-ent. Chemists have long been trying to convert this gas to something useful, and Koji Tanaka and coworkers from the Institute for Molecular Science in Myodaiji, Japan, have now taken an interesting step in this direction. They have developed a ruthenium compound that trans-forms the carbon dioxide into acetone, a solvent used as a paint stripper for oil and enamel paints, in the preparation of glue, and even as a starting material for further chemical synthe-ses.
The problem faced by Tanaka's colleagues in their experiments with carbon dioxide is that the carbon atom in the CO2 molecule is very tightly bound to two oxygen atoms. The carbon would have to break these bonds in order to build larger molecules containing more carbon atoms, which are used for the majority of "useful" chemicals. It does this only very reluctantly - the bonds to the oxygen are too strong.
Tanaka's trick works like this: in an electrolysis apparatus, the Japanese team forces the CO2 to give away one oxygen atom after all by transferring it to another carbon dioxide mole-cule, which is thus transformed into an electrically charged carbonic acid molecule. The re-maining CO fragment is recompensed for its loss by the addition of a ruthenium compound to the reaction mixture. The compound takes the place of the lost oxygen atom and puts a pincer grip on the CO fragment. This doesn't last long however, because the hold is so loose that the pincer can be rapidly pushed aside by the carbon atom of an additional compound mixed into the reactor by the researchers. Once the pincer is completely forced away, the carbon dioxide is transformed to a molecule with three carbon atoms: acetone.
Naturally, the Japanese CO2-cracker is only a first step on the way to explore this gas as a feedstock for the chemical industry. The reaction is not yet sufficiently efficient, and the compound used to force the ruthenium away and form the acetone is expensive. Nevertheless, this reagent contains only single, isolated carbon atoms - and should, in principle, also be derivable from carbon dioxide.


WILEY-VCH Verlag GmbH