Introduction to reactions in supercritical fluids.

In general, reactions fall into two main categories as to why they have been chosen for investigation in supercritical carbon dioxide. The first class exploits the high solubility of the light gases (e.g. Hydrogen and CO) in supercritical carbon dioxide to enhance reaction rates. Hydrogenation and hydroformylation are particularly good examples of this. The second category of reactions investigated in supercritical carbon dioxide are those where enhanced selectivity is observed in the reaction, which usually originates from the unusual solvent properties of supercritical carbon dioxide, and the ability to vary its solvent properties by adjusting pressure. This is potentially the most important and intriguing aspect of synthetic chemistry in supercritical carbon dioxide, and is the area where we have made our most significant contribution. At present, it is also one of the least well investigated and least understood areas, although a number of groups around the world are active in this area.
A considerable amount of reaction chemistry in supercritical carbon dioxide has been reported, and has recently been reviewed.1 There are also two recent books published in the area, one of which describes many aspects synthetic chemistry in SCFs,2 whilst the other concentrates on more physical aspects.3

1. R.S. Oakes, A.A.Clifford and C.M. Rayner, J. Chem. Soc., Perkin Trans. 1, 2001, 917-941.
2. P.G. Jessop and W. Leitner, Chemical Synthesis using Supercritical Fluids, Wiley, VCH, 1999.
3. A.A. Clifford, Fundamentals of Supercritical Fluids, Oxford University Press, 1998.

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