Annex 3.2 Reaction Media for Catalysis

Another biphasic technique uses a fluorinated substance (fluorous phase), which is immiscible with water and most non-fluorinated solvents at room temperature, but which can form a single phase at higher temperatures. Products can thus be separated at room temperature and the soluble catalyst recycled. One such catalyst is made by adding two perfluorinated chains to dba, a classic palladium(0) ligand. 

Ionic liquids have also been used as reaction media (Box 9). The high polarity of quaternary ammonium salts is exploited to favour polar reaction steps. For example, with l- -butyl-3-methylimidazolium tetrafluoborate, 2,7-octadien-l-ol (Section 5.4.3) was obtained in good yield from butadiene and water and was readily separated as it was immiscible with the ionic liquid below 5°C [J. E. L. Dullius, P. A. Z. Suarez, S. Einloft, R. F. deSouza, J. Dupont, J. Fisher and A. DeCian, Organometallics 1998, 17, 815]. 

Supercritical fluids and particularly carbon dioxide can also be useful media for C C bond forming reactions. It should also be pointed out that many of the above procedures, although attractive on a laboratory scale, do involve expensive reagents, ligands, or equipment, and thus are most likely to be applied only in making products of very significantly high value. 

Heterogeneous or heterogenised catalysts (Appendix 2) are extensively used in the form of solid oxides for large industrial production (as shown in Section 5.2), but so far have not found significant uses in fine chemicals manufacture, although some attractive routes have been worked out. For 

---