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Handbook of Solvents - George Wypych - ChemTech - Ventech!

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14.21.2 Predicting cosolvency 1013<br />

f 0.1 0.2 0.4 0.6 0.8 0.9<br />

Glycerol MW = 92.1 Density = 1.2611<br />

mol/L 1.3693 2.7385 5.4771 8.2156 10.9542 12.3235<br />

x 0.0267 0.0580 0.1411 0.2699 0.4964 0.6893<br />

γ, cosolvent 1.257 1.066 0.903 0.899 0.969 0.996<br />

γ, water 1.003 1.010 1.027 1.025 0.979 0.942<br />

Ethylene glycol MW = 62.07 Density = 1.1088<br />

mol/L 1.7864 3.5727 7.1455 10.7182 14.2910 16.0773<br />

x 0.0345 0.0744 0.1765 0.3254 0.5626 0.7432<br />

γ, cosolvent 2.208 1.923 1.494 1.214 1.053 1.013<br />

γ, water 1.002 1.01 1.047 1.12 1.247 1.338<br />

Propylene glycol MW = 76.09 Density = 1.0361<br />

mol/L 1.3617 2.7234 5.4467 8.1701 10.8934 12.2551<br />

x 0.0265 0.0577 0.1405 0.2688 0.4951 0.6881<br />

γ, cosolvent 3.392 2.498 1.567 1.177 1.044 1.019<br />

γ, water 1.005 1.018 1.069 1.145 1.224 1.267<br />

Butylamine MW = 73.14 Density = 0.7414<br />

mol/L 1.0137 2.0273 4.0547 6.0820 8.1094 9.1231<br />

x 0.0199 0.0436 0.1084 0.2149 0.4219 0.6215<br />

γ, cosolvent 6.532 4.498 2.318 1.391 1.042 0.998<br />

γ, water 1.004 1.016 1.071 1.175 1.326 1.384<br />

Under the assumptions that the solute is chemically stable and has little influence on<br />

the activity <strong>of</strong> solvent component, β reflects the extent <strong>of</strong> deviation caused by the<br />

nonideality <strong>of</strong> the solvent mixture, as suggested by Rao et al. 28 However, since β itself is a<br />

complicated function <strong>of</strong> f, equation [14.21.2.13] does not provide additional aid for predicting<br />

cosolvency.<br />

14.21.2.7 Summary<br />

Applications <strong>of</strong> cosolvency in pharmaceutical and environmental research and industries<br />

are briefly summarized. Using ethanol as an example, the effects <strong>of</strong> adding a cosolvent on<br />

the solubilities <strong>of</strong> various organic solutes are presented in Figure 14.21.2.1. The log-linear<br />

solubilization model, equation [14.21.2.2] or [14.21.2.4], is the simplest theory <strong>of</strong><br />

cosolvency developed so far. It discovers general trends and major determinant factors <strong>of</strong><br />

cosolvency, thus providing guidelines for predicting solubility <strong>of</strong> organic chemicals in<br />

mixed solvents. The cosolvency power <strong>of</strong> a specific cosolvent towards a solute <strong>of</strong> interest,<br />

σ, can be estimated with equation [14.21.2.5] with the knowledge <strong>of</strong> the solute octanol-water<br />

partition coefficient Kow. Sources <strong>of</strong> error associated with this estimation method are discussed<br />

based on equation [14.21.2.6]. The slope <strong>of</strong> the σ~log Kow regression, b, can be

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