The use of chemical probes for the characterization of chemical properties is explored for aprotic binary solvent mixtures. The solvatochromic indicators N,N-diethyl-4-nitroaniline, 4-nitroanisole, 4-nitroaniline and 4-nitrophenol were used to characterize binary solvent mixtures of a polar aprotic hydrogen-bond acceptor solvent (ethyl acetate, acetonitrile and dimethyl sulfoxide) with a polychlorinated hydrogen-bond donor solvent (chloroform or dichloromethane). The solvent parameters p*, a and b of the binary mixtures were calculated from the solvatochromic shifts of the indicators. In each case the degree of convergence for a solvent property values obtained from different probes was analyzed. Data obtained by using the non-polar solvatochromic indicator b-carotene are additionally presented. The behavior of the solvent systems was analyzed according to their deviation from ideality due to preferential solvation of the solutes and the complicated intermolecular interactions of the two components of the solvent mixture. The validity of the concept of an intrinsic absolute property of a solvent mixture and whether such a property can be defined by means of chemical probes is discussed. Theoretical equations (preferential solvation models) were used to compute the solvatochromic data. The results were analyzed and related to the solvent effects on some aromatic nucleophilic substitution reactions, comparing the application of single-and multiparametric treatments of solvent effects.

Empirical solvent polarity parameters ET(30) were determined by UV–visible spectrophotometry using Dimroth– Reichardt's betaine dye, as a function of composition, for (aprotic + aprotic) and (aprotic + protic) binary solvent mixtures. For (aprotic + aprotic) solvent systems the cosolvent was toluene, and the other solvents used were selected with different structural characteristics and an extensive range of polarity: chloroform, 1,4‐dioxane, ethyl acetate, tetrahydrofuran, acetone, nitromethane and N,N‐dimethylformamide. For (aprotic + protic) solvent systems, the protic cosolvent used was methanol, and the aprotic solvents selected were toluene, chloroform, 1,1,1‐trichloroethane, tetrahydrofuran, acetone, N,N‐dimethylformamide, and dimethyl sulphoxide. Each system was analysed according to its deviations from additivity due to selective solvation of the betaine. A preliminary application of these empirical solvent polarity parameters was related to the solvent effects in a simple example of a nucleophilic aromatic substitution reaction.

The purpose of this work was to analyze the microscopic feature of binary solvent systems formed by a molecular solvent (acetonitrile or dimethylformamide or methanol) and an ionic liquid (IL) cosolvent [1‐(1‐butyl)‐3‐methylimidazolium tetrafluoroborate or 1‐(1‐butyl)‐3‐methylimidazolium hexafluorophosphate]. The empirical solvatochromic solvent parameters ET(30), π*, α, and β were determined from the solvatochromic shifts of adequate indicators. The behavior of the solvent systems was analyzed according to their deviation from ideality. The study focused on the identification of solvent mixtures with relevant solvating properties in order to select mixed solvents with particular characteristics. The comparison of the molecular–microscopic solvent parameters corresponding to the selected binary mixtures with both ILs considered at similar mixed‐solvent composition revealed that the difference is centered on the basic character of them. A kinetic study of a nucleophilic aromatic substitution reaction between 1‐fluoro‐2,4‐dinitrobenzene (FDNB) and 1‐butylamine (BU) developed in (acetonitrile or dimethylformamide + IL) solvent mixtures is presented in order to investigate and compare the solvent effects on a chemical process. For the explored reactive systems the solvation behavior is dominated by both the dipolarity/polarizability and the basicity of the media, contributing these solvent properties to accelerating the chemical process. Copyright © 2007 John Wiley & Sons, Ltd.

The present work analyzes the solvent effects on the electronic absorption spectra for a set of solvatochromic solutes in several binary mixtures of a polar aprotic hydrogen-bond acceptor solvent with a cosolvent with potential hydrogen-bond donor capability, in terms of preferential solvation models. It compares the response models of the explored mixtures with respect to the chemical properties of the reference probes. It relates the results obtained with the solvatochromic solutes to the solvent effects on an aromatic nucleophilic substitution reaction. It also gives an evaluation of the degree of convergence for the values of a solvent property determined by individual probes, in order to analyze the validity of the solvatochromic indicators for the characterization of mixed solvents.

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