Solvation in supercritical fluids

O. Kajimoto, Solvation in Supercritical Fluids Its Effects on Energy Transfer and Chemical Reactions , Chem. Rev. 1999, 99, 355-389, and references cited therein. 

To date, there have been only a handful of time-resolved studies in dense fluid media (33,34,69-72). Of these, the bulk have focused on understanding a particular chemical reaction by adjusting the solvent environment (69-71). Only over the past two years have there been experiments directed toward studying the peculiar effects of supercritical fluids on these solvation processes (33,34,72). The initial work (33,34) showed that 1) time-resolved fluorescence can be used to improve our understanding of solvation in supercritical fluids and 2) the local solvent composition, about a solute molecule, could change significantly on a subnanosecond time scale. 

Solvation in supercritical fluids depends on the interactions between the solute molecules and die supercritical fluid medium. For example, in pure supercritical fluids, solute solubility depends upon density (1-3). Moreover, because the density of supercritical fluids may be increased significantly by small pressure increases, one may employ pressure to control solubility. Thus, this density-dependent solubility enhancement may be used to effect separations based on differences in solute volatilities (4,5). Enhancements in both solute solubility and separation selectivity have also been realized by addition of cosolvents (sometimes called entrainers or modifiers) (6-9). From these studies, it is thought that the solubility enhancements are due to the increased local density of the solvent mixtures, as well as specific interactions (e.g., hydrogen bonding) between the solute and the cosolvent (10). 

S. C. Tucker, Solvent density inhomogeneities in supercritical fluids, Chem. Rev., 99 (1999) 391—418 O. Kajimoto, Solvation in supercritical fluids Its effects on energy transfer and chemical reactions, Chem. Rev., 99 (1999) 355-89 S. Nugent and B. M. Ladanyi, The effects of solute-solvent electrostatic interactions on solvatochromic shifts in supercritical C02, J. Chem. Phys., 120 (2004) 874-84 F. Ingrosso and B. M. Ladanyi, Solvation dynamics of C153 in supercritical fluoroform a simulation study based on two-site and five-site models of the solvent, J. Phys. Chem. B, 110 (2006) 10120-29 F. Ingrosso, B. M. Ladanyi, B. Mennucci and G. Scalmani, Solvation of coumarin 153 in supercritical fluoroform, J. Phys. Chem. B, 110 (2006) 4953-62 Y. Kimura and N. Hirota, Effect of solvent density and species on static and dynamic fluorescence Stokes shifts of coumarin 153, J. Chem. Phys., Ill (1999) 5474 ... 

Kajimoto O 1999 Solvation in supercritical fluids its effects on energy transfer and chemical reactions Chem. Rev. 99 355-89... 

Petsche, I. B. and P. G. Debenedetti 1991, Influence of solute-solvent asymmetry upon the behavior of dilute supercritical mixtures . J. Phys. Chem. 95, 386. Note that very near the critical point, where the local and long-range effects are well separated, it is fundamentally incorrect to ascribe the bulk compressibility, which grows large as a result of long-range fluctuations, on a local scale, that is, to a local volume element. Nevertheless, these models work relatively well. Kajimoto, O. 1999, Solvation in supercritical fluids Its effect on solubility and chemical reactions . Chem. Rev. 99, 355. 

Sun, Y.-R, C. E. Bunker, and N. B. Hamilton 1993, Ry scale in vapor phase and in supercritical carbon dioxide. Evidence in support of a three-density-region model for solvation in supercritical fluids . Chem. Phys. Lett. 210, 111. 

J Zhang, LL Lee, JF Brennecke. Fluorescence spectroscopy and integral equation studies of preferential solvation in supercritical fluid mixtures. J Phys Chem 99 9268, 1995. 

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