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Solvents

Molecular trees for green chemistry

Nature volume 389, pages 333–334 (1997)Cite this article

Because carbon dioxide is nontoxic, nonflammable, abundant and cheap, it ought to be every scientist's and engineer's favourite solvent for extractions, separations and reactions. Unfortunately, even at dense liquid or supercritical conditions, its ability to dissolve polymeric, ionic or highly polar species is exceedingly limited. On page 368 of this issue1, Cooper et al. show how a fluorinated dendrimer can be used to extract strongly hydrophilic compounds from water into liquid CO2, considerably expanding the applicability of CO2 as a solvent.

CO2 and ‘green chemistry’ have become inextricably intertwined in recent years (the latest example being the “1997 Green Chemistry and Engineering Conference” held in Washington DC on 23-25 June 1997). This may seem ironic in light of the bad press it has endured in connection with global warming, but using CO2 as a solvent does not result in any net production. In fact, most CO2-based processes are designed to recycle and reuse essentially all of the CO2. With this in mind, the excitement about CO2 has developed because of its potential to replace hazardous organic solvents, especially chlorinated liquids and freons. When leaked into the atmosphere these compounds contribute to stratospheric ozone depletion, and the worst of them, the chlorofluorocarbons, have already been banned. In addition, many of the chlorinated solvents are carcinogens or suspected carcinogens, posing a health risk to chemical-plant workers, and to the general public if substantial leaks or spills occur.

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Figure 1: A dendrimer in a droplet of carbon dioxide.

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  1. the Department of Chemical Engineering, University of Notre Dame, Notre Dame, 46556, Indiana, USA

    Joan F. Brennecke

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  1. Joan F. Brennecke
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Brennecke, J. Molecular trees for green chemistry. Nature 389, 333–334 (1997). https://doi.org/10.1038/38611

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