Solvation properties of protic ionic liquid–molecular solvent mixtures

In this study, we have investigated the solvation properties of binary mixtures of PILs with molecular solvents. The selected binary solvent systems are the PILs ethylammonium nitrate (EAN) and propylammonium nitrate (PAN) combined with either water, methanol, acetonitrile or DMSO.

Activation of Electrophile/Nucleophile Pair by a Nucleophilic and Electrophilic Solvation in a SNAr Reaction

Nucleophilic aromatic substitution reactions of 4-chloroquinazoline toward aniline and hydrazine were used as a model system to experimentally show that a substrate bearing heteroatoms on the aromatic ring as substituent is able to establish intramolecular hydrogen bond which may be activated by the reaction media and/or the nature of the nucleophile.

Iso-solvation effects in mixtures of ionic liquids on the kinetics of a model SNAr reaction

The S_NAr reaction between 1-chloro-2,4-dinitrobenzene and morpholine was used as a model system to study solvation effects in a series of mixtures involving imidazolium based ionic liquids.

Solvation chemistry through synergism: static and dynamic features of n-amyl alcohol–chloroform binary solvent mixture

In this paper, we shed some light on the origin of the synergistic solvation structure in a n-amyl alcohol–chloroform (n-PtOH–CHCl₃) binary solvent mixture.

Changes in the SNAr reaction mechanism brought about by preferential solvation

For model S_NAr reactions in mixtures of acetonitrile and water, we found preferential solvation in favor of the aqueous phase.

Origin of strong synergism in weakly perturbed binary solvent system: a case study of primary alcohols and chlorinated methanes

A strong synergistic solvation was observed for the mixtures of hydrogen bond donating and accepting solvent pairs. The nature of the interactions between two solvent pairs was investigated with different dye molecules viz. coumarin 480, coumarin 153, 4-aminophthalimide, and p-nitroaniline. Coumarin 480 in differenet alcohols-CHCl(3) (alcohols: MeOH, EtOH, BuOH) binary mixture shows a strong synergism, which is explained in the backdrop of solvent-solvent interactions. Fluorescence quenching of C480 by 1,2-phenylenediamine in the binary solvent mixture exhibited the maximum deviation in quenching constant corresponding to ~0.45 mol fraction of MeOH in MeOH-CHCl(3) binary mixture and hence suggested the maximum extent of hydrogen-bonding interactions prevailing at this proportion of mixture. The solvation behavior of MeOH-CHCl(3) mixture shows strong probe dependence with no synergism observed in p-nitroaniline, which is ascribed to its higher ground state dipole moment (8.8 D) relative to C480 (6.3 D). Interestingly, the strong synergistic signature observed through spectrophotometric measurement of C480 in alcohol-CHCl(3) binary mixture is absent when studied by fluorescence measurement. The higher excited state dipole moment of coumarin 480 (13.1 D) is considered to be the driving force for the absence of synergism in the excited state. In such strongly perturbed systems (due to high dipole moment values) the dominant phenomenon is preferential solvation. Analysis of proton NMR of MeOH-CHCl(3) binary solvent mixture indicates the existence of MeOH-CHCl(3) clusters in the stoichiometric ratio of 1:2.15. Refractive index measurement also infers the existence of hydrogen bonded network structure between MeOH and CHCl(3). A modified Bosch solvent exchange model has been used to determine the feasibility of synergistic behavior and polarity parameter of the mixed solvent structure of MeOH-CHCl(3) binary solvent mixture.

Estimation of the ground and the first excited singlet-state dipole moments of 1,4-disubstituted anthraquinone dyes by the solvatochromic method

The both, ground-state (mu(g)) and the excited-state (mu(e)) dipole moments of three 1,4-disubstituted anthraquinones, namely 1,4-diaminoanthracene-9,10-dione (1,4-DAAQ), 1-amino-4-hydroxyanthracene-9,10-dione (1,4-AHAQ), and 1,4-dihydroxyanthracene-9,10-dione (1,4-DHAQ) were estimated in binary solvent mixtures (methylcyclohexane-ethyl acetate and ethyl acetate-acetonitrile). The dipole moments (mu(g) and mu(e)) were estimated from Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet, McRae, and Suppan equations by using the variation of Stokes shift with the solvent's relative permittivity and refractive index. The ground-state dipole moments were also calculated theoretically by Gaussian 03 software using B3LYP/6-31 G* level of theory. Further, the change in dipole moment values Deltamu were also calculated by using the variation of Stokes shift with the molecular-microscopic empirical solvent polarity parameter (E(T)(N)). The excited-state dipole moments observed are larger than their ground-state counterparts, indicating a substantial redistribution of the pi-electron densities in a more polar excited state for all the molecules investigated.

Characterization of binary solvent mixtures of DMSO with water and other cosolvents

Binary mixtures of DMSO with nine different cosolvents were characterized in light of the pure solvent scales, using suitable probe/homomorph couples. Various physical (vapor pressure, surface tension, viscosity, and enthalpy of mixing) and spectroscopic (IR and NMR) properties of the DMSO/water mixtures are described in terms of their polarity, acidity, and basicity, and the descriptions are examined with a view to establishing their potential physical significance.

Ion-dipole S(N)2 reaction in acetone-water mixtures. Electrostatic and specific solute-solvent interactions

The rate constants of the S(N)2 reaction of sodium 4-nitrophenoxide (1) and iodomethane were determined by UV-visible spectrophotometry in acetone-water mixtures at 25, 30, and 35 degrees C. The rate-Xwater (mole fraction of water) profile shows that the reaction depends strongly on the medium. The fastest rate constant was obtained in pure acetone, and a minimum occurred at Xwater= 0.4, whereas the observed second-order rate constants increases again in the water-rich region. In pure acetone, in the presence of dicyclohexano-[18]-crown-6, increases linearly with the concentration of the crown ether as a result of the complexation of the sodium ion (KS = 104.8 M) of the ion-pair and the increase in the effective concentration of free 4-nitrophenoxide ion, which was assumed to be the only reactive species. Ion-pairing was also detected at Xwater= 0.65 with a dissociation constant Kd = 7.82 x 10(-4) M(-1). The solvatochromic behaviors of 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)-1-phenoxide (2), 4-[(1-methyl-4(1H)-pyridinylidene)ethylidene]-2,5-cyclohexadien-1-one (3), and 1-methyl-8-oxy-quinolinium betaine (4) were investigated in the entire range of acetone-water mixtures. The dyes presented an increasing order of hydrophilicity compatible with their chemical structure, i.e., 2 < 3 < 4. Kinetic parameters for the methylation of 1 and the ET values of the dyes show a linear correlation of the polarity in the region of Xwater = 1.0-0.40 for 3 and 4, and it was observed that the more hydrophilic the dye the better the correlation coefficient, because of the structural similarity with 1. The activation parameter-Xwater profile shows extrema at Xwater < 0.4, reflecting an important change in the structure of the solvent that is responsible for the changes in the solvation of the reactive species including ion-pairs. These results suggest that the addition of water to acetone reduces abruptly the rate of substitution due to the preferential solvation (PS) of the phenoxide ion by the hydrogen-bonding donor (HBD) solvent. Nevertheless, the real second-order rate constant is "masked" by the association involving Na+ and 4-nitrophenoxide that extends even to water-rich mixtures. A model, based on the assumption that the free-energy terms involved in the second-order rate constant and the dissociation constant of the ion-pair have two components, is invoked to explain the kinetic data. One of the components depends on electrostatic interactions for which the main variable is the dielectric constant of the solvent mixture, and the other depends on the specific solute-solvent interactions, expressed by the activity coefficients of transfer of the species involved. The model indicates that in the range of Xwater = 1.0-0.40 the interactions are exclusively electrostatic, while for the rest of the acetone-rich region they are specific with a large contribution of the 4-nitrophenoxide ion.