Solvatochromism in Binary Mixtures: First Report on a Solvation Free Energy Relationship between Solvent Exchange Equilibrium Constants and the Properties of the Medium

Counterintuitive solvation effect of ionic-liquid/DMSO solvents on acidic C-H dissociation and insight into respective solvation

How would acidic bond dissociation be affected by adding a small quantity of a weakly polar ionic liquid IL (the "apparent" or "measured" dielectric constant ε of the IL is around 10-15) into a strongly polar molecular solvent (e.g., ε of DMSO: 46.5), or vice versa? The answer is blurred, because no previous investigation was reported in this regard. Toward this, we, taking various IL/DMSO mixtures as representatives, have thoroughly investigated the effects of the respective solvent in ionic-molecular binary systems on self-dissociation of C-H acid phenylmalononitrile PhCH(CN)₂ via pK _a determination. As disclosed, in this category of binary media, (1) no linear correspondence exists between pK _a and molar fractions of the respective solvent components; (2) only ∼1-2 mol% of weakly polar ILs in strongly polar DMSO make C-H bonds even more dissociative than in neat DMSO; (3) a small fraction of DMSO in ILs (<10 mol%) can dramatically ease acidic C-H-dissociation; and (4) while the DMSO fraction further increases, its acidifying effect becomes much attenuated. These findings, though maybe counterintuitive, have been rationalized on the basis of the precise pK _a measurement of this work in relation to the respective roles of each solvent component in solvation.

Experimental and theoretical studies on solvation in aqueous solutions of ionic liquids carrying different side chains: the n-butyl-group versus the methoxyethyl group

We used solvatochromic compounds to probe solvation in mixtures of water, W, and four ionic liquids (ILs), 1-R-3-methylimidazoliumX, where R =n-butyl or methoxyethyl and X = acetate and chloride.

Reverse solvatochromism in solvent binary mixtures: a case study using a 4-(nitrostyryl)phenolate as a probe

A 4-(nitrostyryl)phenolate was synthesized and its use in pure solvents revealed a reversion in solvatochromism.

Role of water in determining organic reactivity in aqueous binary solvents

Kinetic data for organic reactions in various binary water-organic solvent mixtures were collected and quantitatively analysed in terms of linear-free-energy relationships by using tert-butyl chloride (2-chloro-2-methylpropane) solvolysis as the reference system. Linear similarity plots for these kinetic data were determined for solvent systems ranging from pure water mixtures up to considerable amount of cosolvent, and 161 similarity coefficients were calculated from slopes of these plots. The existence of these linear plots demonstrated that the solvent effects are of some common nature in all analysed reaction mixtures independent of the reaction type and the cosolvent used. Therefore it was concluded that the observed effects could be connected to the specific solvating properties of water, which govern reactivity even in significant dilution of water by an organic cosolvent. This conclusion was supported by the linear interrelationship between the slopes of similarity plots of different reactions, and hydrophobicity parameters log P of the reacting compounds. The relative solvent effects observed in binary water-organic solvent mixtures were for the first time directly related to the structure of reacting compounds.

Preferential solvation and solvation shell composition of free base and protonated 5, 10, 15, 20-tetrakis(4-sulfonatophenyl)porphyrin in aqueous organic mixed solvents

The solvatochromic properties of the free base and the protonated 5, 10, 15, 20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) were studied in pure water, methanol, ethanol (protic solvents), dimethylsulfoxide, DMSO, (non-protic solvent), and their corresponding aqueous-organic binary mixed solvents. The correlation of the empirical solvent polarity scale (E(T)) values of TPPS with composition of the solvents was analyzed by the solvent exchange model of Bosch and Roses to clarify the preferential solvation of the probe dyes in the binary mixed solvents. The solvation shell composition and the synergistic effects in preferential solvation of the solute dyes were investigated in terms of both solvent-solvent and solute-solvent interactions and also, the local mole fraction of each solvent composition was calculated in cybotactic region of the probe. The effective mole fraction variation may provide significant physico-chemical insights in the microscopic and molecular level of interactions between TPPS species and the solvent components and therefore, can be used to interpret the solvent effect on kinetics and thermodynamics of TPPS. The obtained results from the preferential solvation and solvent-solvent interactions have been successfully applied to explain the variation of equilibrium behavior of protonation of TPPS occurring in aqueous organic mixed solvents of methanol, ethanol and DMSO.