Gaseous miscibility with SCFs

Characteristic properties of SCFs include variable density, dielectric constant viscosity, and cage strength, local inhomogeneity, high diffusion rate, high miscibility with gaseous substances, and high sensitivity of all properties to added substances. All... 

In recent years there has been much interest in the use of supercritical fluids (SCFs) as replacements for conventional liquid solvents, particularly in separation science, but also as reaction media. In addition to their environmental benefits, SCFs have further advantages over conventional liquid solvents, and these are briefly outlined in Section 2. The remainder of the chapter describes the use of SCFs as a medium for NMR spectroscopic studies. First we look briefly at motives for such NMR studies and the techniques employed. We then examine in more detail chemical shifts and nuclear spin relaxation in SCFs. The lower relaxation rates associated with SCFs and consequent sharper lines obtained for quadrupolar nuclei make SCFs excellent solvents. Section 8 describes some NMR studies of organometallic reactions in SCFs. Here the miscibility of supercritical solvents with gaseous reagents proves to be a tremendously useful feature in, for example, homogeneous catalysis. Finally we comment on future possibilities for NMR studies in SCFs. 

The miscibility of SCFs widi gaseous reagents, which allows much higher concentrations of these reagents than is possible in liquid solvents, coupled with the high diffusivity, makes for enhanced rates of reactions involving gases. SCFs have also been employed in polymerizations, radical reactions. 

The total miscibility of SCFs with gases makes them excellent media for reactions involving gaseous reagents... 

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