Many processes that use highly tunable gas-expanded liquids (GXLs) rely on the fact that CO2 addition can greatly affect the polarity of the solvent. We have examined several measures of bulk and local polarity in CO2-expanded acetonitrile to enable more effective exploitation of these polarity changes. The rate of the nucleophilic substitution reaction of tributylamine with methyl p-nitrobenzenesulfonate has been analyzed as a function of solvent composition by using in situ high-pressure UV/vis spectroscopy. We have also measured solvatochromic properties including the Kamlet-Taft pi* parameter and Kosower's Z-value. We correlate these local polarity-based kinetic and solvatochromic measures to develop a better understanding of these property changes as a function of bulk and local solvent composition. The data suggest that local composition enhancement in CO2-expanded acetonitrile has a significant impact on the reaction kinetics.

We seek an improved methodology for the design of solvents and solvent mixtures for separations, especially purification of solids by crystallization. This paper reports new data for the solubility of four multifunctional solids: 3-nitrophthalimide, 5-fluoroisatin, 2-amino-5-nitrobenzophenone, and benzimidazole. The heat of fusion for each solid was measured along with the solubility in several pure and mixed solvents at 283, 298, and 313 K. These data were used to determine new parameters for the MOSCED model for these solids, and those parameters were then used to predict the solid solubility in mixed solvents. The ability to use thermodynamic models to predict solubility of complex solutes provides a new paradigm for the selection of both pure and mixed solvents.