Physical and thermodynamic properties of NCW

In addition, the dielectric constant of NCW is vastly reduced when compared to water at ambient conditions, as shown in Fig. 9.2. Uematsu and Franck correlated the dielectric constant of water as a function of both temperature and density. For example, at 300°C and saturation pressure, the dielectric constant of water is approximately 20, a nearly 75% reduction from the value of 78 at ambient conditions. This dielectric constant most closely corresponds to a moderately polar solvent, such as acetone (dielectric constant = 21.4 at 2 5° C). This reduction in dielectric constant, resulting from a major decrease of the hydrogen bonding relative to ambient water, enables a greatly enhanced solubility of nonpolar organic species in NCW. Increasing the density can increase the dielectric properties of NCW, but kilobar pressures are required. For example, increasing the density at 300°C from saturation conditions p 0.75 g/cm ) to the density of ambient water p = g/cm ) nearly doubles the dielectric constant to approximately 35. 

The reduced dielectric constant of NCW, while increasing the solubility of nonpolar organics, reduces the solubility of inorganic salts. Therefore, for some applications of NCW as a reaction medium, a careful balance must be struck for the desired solubility of ionic and nonionic species to be achieved. Although pressure is a possible variable, normally this will 

To perform chemical transformations on organic substrates in NCW, the medium must be able to dissolve those substrates in sufficient quantities for homogeneous reaction to 

Some example solubility curves for organics in water as a function of temperature are provided in Figs. 9.4-9.6. We choose to discuss four examples of solubility behavior for low 

This closed-loop behavior is typical of hydrogen-bond acceptor molecules (nicotine is an example), as the balance between effects of enthalpy and entropy leads to higher solubility at lower temperatures, then a drop as hydrogen bonding begins to break down, then a second increase as the entropic forces take control. The use of this type of behavior makes certain functional groups (ethers, esters) most useful for separations in NCW systems. 

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