Isodielectric solvent mixtures

This equation corresponds to Eq. (28) of Covington et (Part 2), who found that AG values from electrochemical and spectroscopic experiments agree satisfactorily in mixtures of isodielectric solvents. Relations between AG and 6 have also been treated which involve change of solvation number and nonstatictlcal distribution of the solvated species. ... 

The reaction [9.104] also has been studied for isodielectric mixtures of alcohol-chlorobenzene with 8=20,2 (permittivity of pure n-propanol) and 8=17.1 (permittivity of pure n-butanol) to investigate flic relative effect of universal and specific solvation on the resolvation process. The mixtures were prepared by adding chlorobenzene to methanol, ethanol, and C1-C3 alcohol. Alcohol is a solvate-active component in these isodielectric solvents. K s data are given in Table 9.6. 

The expression for the standard molar Gibbs energy of transfer is similar to Equation 6.24, but in terms of the mole fractions rather than the volume fractions used by Cox et al. [75]. However, A G (I, A -> A + B) has an additional term that is related to the electrostatic effect of the transfer from the source solvent with permittivity to the solvent mixture with its different permittivity (unless transfer is between isodielectric solvents). 

A great variety of aqueous—organic mixtures can be used. Most of them are listed in Table I with their respective freezing point and the temperature at which their bulk dielectric constant (D) equals that of pure water. These mixtures have physicochemical properties differing from those of an aqueous solution at normal temperature, but some of these differences can be compensated for. For example, the dielectric constant varies upon addition of cosolvent and cooling of the mixture in such a way that cooled mixed solvents can be prepared which keep D at is original value in water and are isodielectric with water at any selected temperature (Travers and Douzou, 1970, 1974). 

When molecules of both solvents only weakly interact specifically, the last term of Eq. (66) can be neglected for isodielectric mixtures. Such a simplified equation was used [255] for the calculation of the AG of Ag(I) and Cu(I) from AN or DMSO to their mixtures with other solvents. A good agreement was found between the calculated and the experimental data. 

In binary mixtures of MeOH, AN and NM having an almost constant Er, /-AmaBuN salts are dissociated but the variation of the Walden product with solvent composition suggests specific ion-solvent interactions. D Aprano and Fuoss observed specific effects on the conductance of the Pic", Br" and BPh of Bu4N in isodielectric mixtures of dioxan with water, MeOH, AN and / -nitroaniline (PNA). and the... 

Attempts to correlate rate constants with solvent dielectric functions are not always successful. A marked lack of correlation between logk and D, IID, or (D — 1)/(2D + 1) has been reported for the addition of 2,2 -bipyridyl to [Ni(dtp)2] and for dissociation of the [Fe(phen)s] + cation. Interestingly, aquation rates for the [Fe(5-NOaphen)3] + cation in hydrogen peroxide-water mixtures vary markedly with solvent composition despite the almost isodielectric properties of these mixtures. ... 

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