Mixed-aqueous solvent, transfer

Heat Capacities and Volumes of Transfer of Electrolytes from Water to Mixed Aqueous Solvents... 

In recent years we have undertaken a systematic investigation of the volumes and heat capacities of transfer of alkali halides and tetraalkylammonium bromides from water to mixed aqueous solvents (1-6). These properties are important because, when combined with enthalpies and free energies, they can be used to calculate the temperature and pressure dependences of various equilibrium properties of electrolytes in mixed solvents. Since the properties of electrolytes in mixed aqueous solvents are closely related to the corresponding properties of the nonelectrolyte in an electrolyte solution, infor-... 

Solute-Solute Model. The observed transfer functions of electrolytes in the mixed aqueous solvents are not simple, and they show various maxima and minima in the cosolvent concentration dependence—especially with hydrophobic... 

In principle, the transfer chemical potentials recently published for [Fe(bipy)3f and [Fe(phen)3] for transfer from water into methanol-water mixtures should be valuable in the interpretation of solvent effects on reactivities of these cations, but unfortunately the authors derivations are unreliable. There are errors in calculating solubility products and transfer chemical potentials for the salts studied the transfer chemical potentials for the perchlorate anion are ignored (a serious error in methanol-rich mixtures) and there are transcription or printing errors in their published Table 3 for methanol contents of above 44.7%. Acceptable transfer chemical potentials for the [Fe(phen)3] cation, for these and other mixed aqueous solvent media, are available from van Meter and Neumann. ... 

Enthalpies of transfer of trihalides from water into nonaqueous and mixed solvents can be obtained by simple arithmetic for all the cases where enthalpies of solution in nonaqueous and mixed aqueous media are known. As long as the enthalpies concerned have been measured in reasonably dilute conditions, or have been estimated for infinite dilu-... 

In principle, Gibbs free energies of transfer for trihalides can be obtained from solubilities in water and in nonaqueous or mixed aqueous solutions. However, there are two major obstacles here. The first is the prevalence of hydrates and solvates. This may complicate the calculation of AGtr(LnX3) values, for application of the standard formula connecting AGt, with solubilities requires that the composition of the solid phase be the same in equilibrium with the two solvent media in question. The other major hurdle is that solubilities of the trichlorides, tribromides, and triiodides in water are so high that knowledge of activity coefficients, which indeed are known to be far from unity 4b), is essential (201). These can, indeed, be measured, but such measurements require much time, care, and patience. 

Solubilities, in water, ethanol, and ethanol-water mixtures, have been reported for [Fe(phen)3]-(0104)2, [Fe(phen)3]2[Fe(CN)6], and [Fe(phen)3][Fe(phen)(CN)4]. Solubilities of salts of several iron(II) iiimine complexes have been measured in a range of binary aqueous solvent mixtures in order to estimate transfer chemical potentials and thus obtain quantitative data on solvation and an overall picture of how solvation is affected by the nature of the ligand and the nature of the mixed solvent medium. Table 8 acts as an index of reports of such data published since 1986 earlier data may be tracked through the references cited below Table 8, and through the review of the overall pattern for iron(II) and iron(III) complexes (cf. Figure 1 in Section 5.4.1.7 above) published recently. ... 

The densities and volumetric specific heats of some alkali halides and tetraalkylammonium bromides were undertaken in mixed aqueous solutions at 25°C using a flow digital densimeter and a flow microcalorimeter. The organic cosolvents used were urea, p-dioxane, piperadine, morpholine, acetone, dime thy Isulf oxide, tert-butanol, and to a lesser extent acetamide, tetrahydropyran, and piperazine. The electrolyte concentration was kept at 0.1 m in all cases, while the cosolvent concentration was varied when possible up to 40 wt %. From the corresponding data in pure water, the volumes and heat capacities of transfer of the electrolytes from water to the mixed solvents were determined. The converse transfer functions of the nonelectrolyte (cosolvent) at 0.4m from water to the aqueous NaCl solutions were also determined. These transfer functions can be interpreted in terms of pair and higher order interactions between the electrolytes and the cosolvent. 

Hefter, G., Marcus, Y., and Waghome, W. E. (2002) Enthalpies and entropies of transfer of electrolytes and ions from water to mixed aqueous organic solvents, Chem. Rev. 102, 2773-2835 and references cited therein. 

The expression for the excess Gibbs energy is built up from the usual NRTL equation normalized by infinite dilution activity coefficients, the Pitzer-Debye-Hiickel expression and the Born equation. The first expression is used to represent the local interactions, whereas the second describes the contribution of the long-range ion-ion interactions. The Bom equation accounts for the Gibbs energy of the transfer of ionic species from the infinite dilution state in a mixed-solvent to a similar state in the aqueous phase [38, 39], In order to become applicable to reactive absorption, the Electrolyte NRTL model must be extended to multicomponent systems. The model parameters include pure component dielectric constants of non-aqueous solvents, Born radii of ionic species and NRTL interaction parameters (molecule-molecule, molecule-electrolyte and electrolyte-electrolyte pairs). 

Another component of the ATRP equilibrium constant, the halidophilicity, also depends upon the nature of the transferable atom (and the ligand). In systems where the halidophilieity is low, the XCu Ln eomplex can easily dissociate to halide ions and Cu°L whieh cannot deactivate radieals, and the dissociative loss of deaetivator ultimately leads to fast reaetions (eq. 2) that are poorly controlled (eq. 3). It has been shown that halidophilieity is low in protic media, and it decreases signifieantly in mixed organie-aqueous solvents as the amount of water is inereased. ("25,24) The amount of deaetivator present in the reaction system depends on the halidophilieity and on the total eoneentrations of Cu species and halide ions, aeeording to eq. 4. Therefore, to minimize the dissociation of deaetivator in systems where the halidophilieity is low, extra Cu eomplex and / or halide salts should be added. This has been shown to improve the polymerization control.("25,25,2d) Halidophilicity is discussed in more detail in the following sections. 

Harris FE, Rice SA (1954) A chain model for polyelectrolytes. Int J Phys Chem 58 725-732 Heller GT, Marcus Y, Waghorne WE (2002) Enthalpies and entropies of transfer of electrolytes and ions from water to mixed aqueous organic solvents. Chem Rev 102 2773-2836 Helgeson HC, Kirkham DH, Flowers GC (1981) Theoretical prediction of the thermodynamic behavior of aqueous electrolytes at high pressures tmd temperatures IV. Calculation of activity coefficients, osmotic coefficients, and apparent moled and standard and relative partial moM properties to 600 °C and 5 kb. Am J Sci 281 1249-1516 HeplerLG, Hovey JK (1996) Standard state heat capacities ofaqueous electrolytes and some related undissociated species. Can J Chem 74 639-649... 

Marcus Y (2005a) BET nodehng of solid-liquid phase diagrams of common ion binary stilt hydrate mixtures. 1. The BET parameters. J Sol Chem 34 297-306 Marcus Y (2006) On the molar volumes and viscosities of electrolytes. J Sol Chem 35 1271-1286 Marcus Y (2007) Gibbs energies of transfer of anions from water to mixed aqueous organic solvents. Chem Rev 107 3880-3897... 

Tetraalkylammonium salts have been used as phase transfer catalysts for alkylation [5], sulfonylation [46], and benzoylation reactions [47] of carbohydrate derivatives in mixed organic/aqueous solvent. For example, benzyhdene-protected methyl a-glucopyranoside underwent selective benzylation at the more acidic 2-OH group in the presence of a phase transfer catalyst (Scheme 11). 

An extra thermod3mamic assumption is required in order to describe the transfer properties of individual ions, and consistent values, obeying AtGi°° = Hi°° — TAiSi°°, are obtained when the transfer quantities of Pli As and BPh4 are assumed to be equal (the TATB assumption) as is widely employed [6]. The results for transfer of ions into many pure organic solvents have been summarized by Marcus [1] and those for transfer into mixed aqueous-organic solvents by him with coworkers [7]. 

The standard molar Gibbs energies of transfer of ions from water to nonaqueous solvents are dealt with in Section 4.3.2.1 and those for transfer into mixed aqueous-organic solvents in Section 6.1. Specifically, the standard molar Gibbs energies of transfer of hydrogen ions from water to solvents S, A G"(H, W S), are available in Table 4.2 for nonaqueous solvents, in Table 6.1 for equimolar mixtures of water with cosolvents, and in the compilations by Kalidas et al. [17] and by Marcus [18] for other compositions. The pH scale is a universal one, because it refers to the same standard state, infinite dilution of hydrogen ions in pure water, where its activity coefficient is unity. The acidity in other solvents, pH, is related to this universal one by Equation 8.8. 

---