Solvation in pure and mixed solvents: Some recent developments

Seoud, Omar A. El

doi:10.1351/pac200779061135

Cited by 71 publications

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References 147 publications

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“…More discussion on the subject can be found in specialized books, and review articles. [2][3][4][5][6][7][8][9][10][11] The reason for the multi-parameter dependence of chemical phenomena on solvent properties, point (i) above, is that several solutesolvent interactions come into play; their effects should be taken into account. These include both specific and non-specific interactions, e.g., hydrogen-bonding, dipolar-interactions (ion-dipole, dipoledipole, dipole-induced dipole), and dispersion or London interactions.…”

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confidence: 99%

“…19 As an example of the determination of the relative importance of solute-solvent interaction mechanisms, consider the solvation of solvatochromic probes. The procedure in order to extract this information is as follows: 10,11 we determine the effects of a group of solvents on the Uv-vis spectra of one or more probes; we apply Equation 2 in order to calculate E T (probe); we use Equation 3 in order to calculate the regression coefficients (a), (b), (s), and (p). Finally, we draw conclusions about the relative importance of solvent acidity, basicity, etc., from these regression coefficients, after their values are statistically standardized (i.e., from b statistical (regression coefficient)), in order to make them comparable.…”

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“…These, after algebraic manipulation, lead to the following solvent exchange equilibria, termed solvent "fractionation factors" j: 10,11 (8) (9) Figure 5. (10) where (m) represents the number of solvent molecules whose exchange in the probe solvation shell affects E T (probe); usually m ≤ 2, Bk refers to bulk solvent, and the concentrations of the solvent species are "effective" not analytical ones.…”

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“…(10) where (m) represents the number of solvent molecules whose exchange in the probe solvation shell affects E T (probe); usually m ≤ 2, Bk refers to bulk solvent, and the concentrations of the solvent species are "effective" not analytical ones. Note that (m) should not be confused with the total number of solvent molecules that solvate the probe.…”

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confidence: 99%

“…Our results have shown that the magnitude of this energy is sizeable (e.g., range from 2.1 to 3.7 kcal mol -1 over a 50 o C range for WB in aqueous alcohols) relative to the activation enthalpies of many organic reactions. 10,11 …”

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Solvation simplified

Seoud¹

2010

Quím. Nova

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Recebido em 24/5/10; aceito em 28/9/10; publicado na web em 16/11/10The effects of solvents on chemical phenomena is complex because there are various solute-solvent interaction mechanisms. Solvatochromism refers to the effects of solvents on the spectra of probes. The study of this phenomenon sheds light on the relative importance of the solvation mechanisms. Solvation in pure solvents is quantitatively analyzed in terms of a multi-parameter equation. In binary solvent mixtures, solvation is analyzed by considering the organic solvent, S, water, W, and a 1:1 hydrogen bonded species (S-W). The applications of solvatochromism to understand distinct chemical phenomena, reactivity and swelling of cellulose, is briefly discussed.Keywords: solvation ; solvatochromism; solute-solvent interactions.The need for understanding solvation is clear: most reactions are carried out in the liquid phase; the solvent is not a "spectator". It acts as a heat-and mass-transfer agent; it participates in proton transfers (for acid/base catalyzed reactions) and in the solvation of ions, dipolar species, etc. Consider the decomposition of 6-nitro-3-carboxybenzisoxazole, whose reaction scheme is depicted in Figure 1. This example is particularly illustrative of the effects of solvents on reactivity because it is a simple, spontaneous decomposition reaction. Therefore, effects of changing the solvent on the observed rate constant, k obs , can be unequivocally attributed to differences in solvation between the reactant state-where the negative charge is concentrated on the carboxylate anion-and the transition state, where the charge is dispersed over several atoms. The half-lives of this reaction in hexamethylphosphotriamide, acetonitrile, and water, are 0.001 s, 11.6 min, and one day, respectively! 1Can these large differences in k obs be correlated with solvent properties? The results of such attempt is shown in Table 1, where the subscript (S) refers to solvent, e r , E T (30), a S , b S refer to the solvent relative permittivity, its empirical polarity, hydrogen-bond donation capacity or "acidity", and hydrogen-bond acceptance capacity or "basicity", respectively (vide infra for more discussion of the last three solvent descriptors). Table 1 reveals that there is no correlation between log k obs and any single solvent property. Inclusion of a second descriptor leads to a noticeable improvement in the regression analysis; a four-descriptor equation gives the best correlation coefficient. The conclusion from Table 1 is obvious: solvent effects on chemical reactivity, and presumably other phenomena, e.g., chemical equilibria and spectroscopic data, are complex; any successful correlation with a single solvent descriptor is, most certainly, fortuitous.The following questions now arise: (i) What is the reason for this complex dependence of chemical phenomena on solvent properties?(ii) Can the relative importance of each solute-solvent interaction be identified and quantified? (iii) How can we treat solvation in solvent mixtures? The object...

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