Green solvents additional references

Supercritical fluids (SCFs) have long fascinated chemists and over the last 30 years this interest has accelerated. There is even a journal dedicated to the subject— the Journal of Supercritical Fluids. These fluids have many fascinating and unusual properties that make them useful media for separations and spectroscopic studies as well as for reactions and synthesis. So what is an SCF Substances enter the SCF phase above their critical pressures P and temperatures (Tc) (Figure 4.1). Some substances have readily accessible critical points, for example for carbon dioxide is 304 K (31 °C) and is 72.8 atm, whereas other substances need more extreme conditions. For example for water is 647 K (374 °C) and P is 218 atm. The most useful SCFs to green chemists are water and carbon dioxide, which are renewable and non-flammable. However, critical data for some other substances are provided for comparison in Table 4.1. In addition to reactions in the supercritical phase, water has interesting properties in the near critical region and carbon dioxide can also be a useful solvent in the liquid phase. Collectively, carbon dioxide under pressurized conditions (liquid or supercritical) is sometimes referred to as dense phase carbon dioxide. 

ILs are organic salts with unusually low melting points, well below 100 C [1, 2]. These substances have been suggested as potentially green replacements for traditional molecular solvents since some ILs are nonvolatile, nonflammable, thermally stable, and recyclable. Additionally, they open the path to novel methods that are not possible using classical solvents. Those formed by the transfer of a proton between a Brpnsted acid and a Brpnsted base form the protic subgroup now referred to as Protic Ionic Liquids (PlLs) [3,4]. 

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