The main purpose of this work is to analyze the microscopic feature of solvent systems resulting from the basis of binary mixtures formed by a protic molecular solvent (methanol, ethanol, propan-1-ol, propan-2-ol, and 2-ethoxyethanol) and a 1-butyl-3-methylimidazolium (bmim)-based ionic liquid (IL) cosolvent composed of different anions (tetrafluoroborate, hexafluorophosphate, chloride, and bromide). At the same time, a complementary aim is to evaluate the incidence of anion type on the solvation pattern. The empirical solvatochromic parameters E(T)(N), π*, β, and α were determined from the UV-vis solvatochromic shifts of adequate probes. The behavior of the solvent systems was analyzed according to their deviation from ideality. E(T)(N) polarity and π* dipolarity/polarizability exhibit positive deviation from ideal behavior in all binary mixtures at the explored compositions. Moreover, E(T)(N) and α parameters display synergetic effects in some binary mixtures composed of tetrafluoroborate and hexafluorophosphate anions. The influence of anion nature on the response patterns is clearly manifested in the basicity β and acidity α of the media. This is connected with the degree and type of interaction between the anions and the 1-butyl-3-methylimidazolium cation. The ion-pair character of the ionic liquids affects their interactions with a solute or a molecular solvent. The application of an appropriate preferential solvation model allowed us to obtain valuable information about solute-solvent and solvent-solvent interactions of the selected ionic liquid mixtures. It is possible to identify relevant mixtures paying particular attention to the most remarkable microscopic properties, the acidity and the basicity, in order to propose "new solvents". Thus, the solvating feature can be tailored selecting the molecular and/or the ionic component at a particular composition. A simplified combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K) equation is shown to satisfactorily predict the solvatochromic parameters within [protic molecular solvent + bmim-based IL].

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aThe type of specific intermolecular and interionic interactions that are established when an ionic liquid is dissolved in water was here analysed. The study of the solvatochromic response of dipolarity micro-sensors based on Reichardt E T (30) and Kamlet-Abboud-Taft solvent scales and the application of the solvent exchange model confirmed the formation of different intersolvent complexes in binary mixtures of (water + [C 4 mim] [BF 4 ]/[Br]) type. These complexes provide H-bond or electron pairs to the polar network, respectively. Moreover, for 4-methoxybenzenesulfonyl chloride hydrolysis reaction in the (water + [C 4 mim] [BF 4 ]) system, a higher inhibition (13 times) on the k obs values was observed. Multiple linear regression analysis that allows confirming the solvent effect upon the reactive system is due to the hydrogen-bond donor properties of intersolvent complex formed. Then, the correlation between two different solvent-dependent processes proved to be successful.

The reactive behaviour of protic ionic liquids (PILs) has been shown to be governed not only by their chemical structures but also by their global compositions, which include the presence of free acids and bases at equilibrium with ionic pairs. Six PILs composed of primary, secondary, or tertiary alkyl ammonium cations with two couterions, nitrate or acetate, were tested in model reactions with unsaturated substrates. The free species that were naturally present in these liquids were identified by cyclic voltammetry. Only tributylammonium nitrate was found to be mostly composed just of the ionic pair; the other five PILs also contain variable amounts of free acid and amine. In reactive systems, these free species determine the products of the reaction. In particular, allylic amines and β‐amino esters were obtained in good yields (91 and 75 %, respectively) by reaction of conjugated dienes and acrylates in the presence of PILs. By taking into account the actual composition of each PIL, it was possible to direct the reaction path towards a specific product with good yields, to ensure acid catalysis, to avoid polymerization of the substrate, and to promote phase transfer of products. These results establish some useful guidelines for the rational design of new PIL‐based one‐step synthetic strategies.