Solvatochromic study on nitroanilines. Preferential solvation vs dielectric enrichment in binary solvent mixtures

The preferential solvation approach and the dielectric enrichment model have been applied to explain the solvatochromic behavior of o-, m- and p-nitroaniline (oNA, mNA and pNA) in several binary solvent mixtures. Cyclohexane was used as the “inert” nonpolar cosolvent in every mixture. The other solvents were chosen trying to vary their polarity as much as possible as well as their hydrogen bond donor or acceptor capabilities. Preferential solvation is detected in every solvent mixture studied. These global interactions were quantified by calculating the preferential solvation constant, K. Also, by using the previously developed model, we calculated for each pair of solvent mixtures a theoretical curve and the corresponding K_D due to dielectric enrichment. Non hydrogen bond acceptor solvents (β=0), give values of K quite similar to those of K_D, indicating that the preferential interaction is practically dielectric in nature. When the interacting solvent is a hydrogen bond acceptor, the values of K are higher than K_D according to the acidity of the H in the amino group in the solutes. The values of K as well as of K_D for any solvent mixtures in general follow the order pNA > mNA > oNA as expected, considering the values of μ_g and μ_g-μ_ex. Studies in pure solvent support previous conclusions.     

Determination of reorganization energy of fluorenone and 4-hydroxyfluorenone in neat and binary solvent mixtures

Steady-state absorption and fluorescence measurements of fluorenone and 4-hydroxyfluorenone in neat and binary solvent mixtures were used to explore the reorganization energy in liquid system. The results of spectroscopic measurements were used to calculate, according to Marcus theory, the outer-sphere solvent reorganization energy, lambda(0), and the internal molecular reorganization energy, lambda(in). Preferential solvation of fluorenone and 4-hydroxyfluorenone in binary solvent mixtures has been studied by monitoring the outer-sphere solvent reorganization energy. In cyclohexane-tetrahydrofuran mixtures, the deviation from linearity in the lambda(0) versus the solution polarity is due to non-specific dipolar solvent-solute interactions. For cyclohexane-ethanol binary mixtures, both non-specific and specific (hydrogen bond) interactions contribute to the observed changes.     

Infrared study of 6-methylcoumarin in binary solvent mixtures

The infrared absorption spectra of the carbonyl stretching vibrations of 6-methylcoumarin (6MC) have been investigated in CCl4/ROH mixtures (CCl4/C2H5OH, CCl4/n-C3H7OH, CCl4/i-C3H7OH, and CCl4/t-C5H11OH). Two types of carbonyl stretching vibration bands for 6MC are found with the change of the mole fraction of the aprotic solvent CCl4(X CCl4 in binary solvent mixtures. The dependencies of the frequencies of carbonyl stretching vibrations upsilon(C=O) on X CCl4 allow a distinction and assignment of all species resulting from the solvent-solute interactions. Linear correlations between the upsilon(C=O) of each species and X CCl4 are found. The influence on the transformation of some species caused by the self-associated alcohols is discussed.     

Sensitized photoxygenation of piroxicam in neat solvents and solvent mixtures.

Detection of O(2)(1Delta(g)) phosphorescence emission, lambda(max)=1270 nm, following laser excitation and steady state methods were employed to determine the total rate constant, k(T), for the reaction between the non-steroidal anti-inflammatory drug piroxicam (PRX) and singlet oxygen in several solvents. Values of k(T) ranged from 0.048+/-0.003 x 10(6) M(-1) s(-1) in chloroform to 71.2+/-2.2 x 10(6) M(-1) s(-1) in N,N-dimethylformamide. The chemical reaction rate constant, k(R), was determined by using thermal decomposition of 1,4-dimethylnaphthalene endoperoxide as the singlet oxygen source. In acetonitrile, the k(R) value is equal to 5.0+/-0.4 x 10(6) M(-1) s(-1), very close to the k(T) value. This result indicates that, in this solvent, the chemical reaction corresponds to the main reaction path. Dependence of total rate constant on the solvent parameters pi* and beta can be explained in terms of a reaction mechanism that involves the formation of a perepoxide intermediate. Rearrangement of the perepoxide to dioxetane followed by ring cleavage and transacylation accounts for the formation of N-methylsaccharine and N-(2-pyridyl)oxamic acid, the main reaction products. Data obtained in dioxane-water (pH 4) mixtures with neutral enolic and zwitterionic tautomers of piroxicam in equilibrium show that the zwitterionic tautomer reacts with singlet oxygen faster than the enolic tautomer.     

Cs NMR study of the cryptand-222-Cs complex in binary solvent mixtures

The formation constants of the cryptand-222 complex with the cesium ion were studied by ¹³³Cs NMR measurements in four binary solvent systems: acetonedimethylsulfoxide (Me₂Co---Me₂SO), acetonitrile (MeCN)---Me₂SO, propylene carbonate(PC)---Me₂SO and PC-dimethylformamide (DMF). In the neat solvents the formation constant increases in the order Me₂SO < DMF < Me₂CO < PC < MeCN, which is the inverse order of their solvating abilities as given by the Gutmann donor number. In binary mixtures the stabilities varied monotonically with the decomposition. As expected, there is no correlation between the stabilities of the complexes and the dielectric constant of the medium. It seems that, for aprotic solvents with similar Pearson basicities and in the absence of ion pair formation, the donor ability of a binary solvent mixture can be qualitatively predicted from the donicities of the two solvents and the composition of the mixture.     

Electrochemical study of 18-crown-6-Tl+ complexes in binary solvent mixtures

Summary The formation constants,K _S, of the 18-crown-6 complex with thallium(I) ion were studied by polarographic measurements in binary mixtures of acetonitrile, acetone, tetrahydrofuran, and dimethylsulfoxide with water, as a function of the solvent mole fraction. In all the cases, the variation of the stability constant can be described by the empirical relation logK _S=a[(–1)/(2+1)]+b where stands for relative permittivity of a given mixture anda andb mark the regression coefficients. The values ofa calculated for four series of binary mixtures showed correlation with the Gutmann donor numbers of the neat organic solvents which form the mixture.On leave from the Department of Chemistry, Jingzhou Teacher's College, Jingzhou, Hubei, China     

Preferential solvation of phenol in binary solvent mixtures. A molecular dynamics study

Molecular dynamics computer simulations were carried out to study the preferential solvation of phenol in equimolar acetonitrile-water and ethanol-water binary mixtures. Two water models were used to investigate the model dependence of preferential solvation. The results are compared to recent intermolecular 1H NOESY experiments reported on the same systems. In the case of acetonitrile-water the local mole fraction obtained from simulations agrees quite well with experiments. In the case of ethanol-water there was a qualitative difference, which was observed for both water models. However, when comparing the degree of preferential solvation of the two cosolvents ethanol and acetonitrile with each of the two water models, the trend obtained from the simulations agrees with experimental data.     

Solvatochromic parameters for binary mixtures and a correlation with equilibrium constants. Part I. Dioxane-water mixtures

The values of the solvatochromic parameters and were determined at 25°C for dioxane-water mixtures from 0 to 100% of dioxane. These values as well as those of the Reichardt polarity parameter E _T (30) and the polarity-polarizability ^* are correlated with acid dissociation constants and other equilibrium constants in solvent mixtures of the same composition. As a general rule, two linear zones with different slopes are obtained, one zone covering water-rich solutions, and the other dioxane-rich solutions. The change in behavior takes place at about 55% (v/v) dioxane for all equilibria studied. A fit of pK to an equation of the multiparametric form proposed by Kamlet and Taft shows in most cases a linear dependence on ^* alone, in other cases a dependence on ^* and .     

The interaction of patterned solutes in binary solvent mixtures

Mean solute-solute forces and solute-induced solvent structure are investigated for pairs of chemically patterned (patched) solutes in binary mixtures near demixing coexistence. The isotropic and anisotropic hypernetted-chain integral equation theories as well as a superposition approximation are solved and compared. The patched solutes consist of one end that favors the majority species in the mixture while the other end favors the minority species. A wide range of patch sizes is considered. The isotropic and anisotropic theories are found to be in good agreement for most orientations, including the most attractive and most repulsive configurations. However, some differences arise for asymmetrical orientations where unlike ends of the solute particles face each other. In contrast, superposition often gives a rather poor approximation to the mean force, even though the results obtained for the solvent densities agree qualitatively with the anisotropic theory. The mean force is sensitive to small differences in the densities particularly near demixing. For patched solutes the influence of demixing-like behavior is evident both in the orientational dependence and in the range of the mean force acting between solutes.     

Thermodynamics of binary mixtures: excess volumes of mixing of some binary 1,2-dichloroethane mixtures

The excess volumes, V^E, of some binary 1,2-dichloroethane mixtures have been determined at 30°C. The data have been examined for Cell model theory of Prigogine and Flory's theory. Both theories have been found to fail to fit the results with useful accuracy.     

Raoult's law as applied to binary solvent mixtures

The inapplicability of the original statement of Raoult's law to binary solvent mixtures has been known for many years. An appropriate form for binary solvent mixtures is developed from the fundamental thermodynamic concept of fugacity, and is shown to be quantitatively applicable to the water+tetrahydrofuran solvent system and qualitatively applicable to the results which have been obtained for other aqueous organic solvent mixtures.     

Thermochemistry of 1-bromoadamantane in binary mixtures of water-aprotic solvent

Solution enthalpies of 1-bromoadamantane in the mixed solvents water-N,N-dimetylformamide, water-N,N-dimethylacetamide and water-acetone were determined at 298.15 K, within the range of solubility of 1-bromoadamantane (1-BrAd) in the mixed solvents. The solution enthalpy of 1-bromoadamantane in water was determined based on extrapolation from the three mixtures. Enthalpies of transfer from the mixed solvents to cyclohexane were calculated. The effect of the composition of the mixtures on the thermochemical values obtained was also investigated.     

Solvatochromic parameters for binary mixtures of an ionic liquid with various protic molecular solvents

Abstract  Solvatochromic parameters (E _T ^N, normalized polarity parameter; π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) have been determined for binary mixtures of propan-2-ol, propan-1-ol, ethanol, methanol and water with recently synthesized ionic liquid (IL; 2-hydroxyethylammonium formate) at 25 °C. In all solutions except aqueous solution, E _T ^N values of the media increase abruptly with the ILs mole fraction and then increase gradually to the value of pure IL. A synergistic behavior is observed for the α parameter in all solutions. The behavior of π* and β are nearly ideal for all solutions except for solutions of methanol with the IL. The applicability of nearly ideal combined binary solvent/Redlich–Kister equation was proved for the correlation of various solvatochromic parameters with solvent composition. The correlation between the calculated and the experimental values of various parameters was in accordance with this model. Solute–solvent and solvent–solvent interactions were applied to interpret the results. Graphical Abstract  Predicted values of solvatochromic parameters (SP) (E _T ^N, normalized polarity parameter; π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) from the correlation equations versus its experimental values for binary mixtures of 2-hydroxyethylammonium formate with water, methanol, ethanol, propan-1-ol and propan-2-ol.      

Solvatochromic parameters for binary mixtures of an ionic liquid with various protic molecular solvents

Abstract  

Solvatochromic parameters (E _T ^N, normalized polarity parameter; π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) have been determined for binary mixtures of propan-2-ol, propan-1-ol, ethanol, methanol and water with recently synthesized ionic liquid (IL; 2-hydroxyethylammonium formate) at 25 °C. In all solutions except aqueous solution, E _T ^N values of the media increase abruptly with the ILs mole fraction and then increase gradually to the value of pure IL. A synergistic behavior is observed for the α parameter in all solutions. The behavior of π* and β are nearly ideal for all solutions except for solutions of methanol with the IL. The applicability of nearly ideal combined binary solvent/Redlich–Kister equation was proved for the correlation of various solvatochromic parameters with solvent composition. The correlation between the calculated and the experimental values of various parameters was in accordance with this model. Solute–solvent and solvent–solvent interactions were applied to interpret the results.     

Primary photoprocesses in molecules of carbocyanine dyes in binary solvent mixtures

The effect of the composition of the dimethyl sulfoxide (DMSO)-toluene mixture on the photophysical processes of thia-, indo-, and imidacarbocyanine dyes was studied. In the mixtures with the DMSO content of more than 20 vol %, the dyes representing solvated cations are characterized by high efficiency of trans → cis photoisomerization and fluorescence, in contrast to the extremely low efficiency of intersystem crossing to the triplet state. With growing the toluene content in the mixture, ion pairs between the dye cation and Cl⁻, Br⁻, I⁻, or BF⁴⁻ anion are formed. In the cases when the dye counterions are Br⁻ or I⁻, a sharp increase in the yield of the triplet molecules and a decrease in their lifetime take place. The results are discussed in terms of “the external heavy atom effect” in ion pairs.     

Solubility of carbazole in binary chloroalkane + dibutyl ether solvent mixtures

Solubilities are reported for carbazole in three binary chloroalkane + dibutyl ether solvent mixtures at 25°C. Results of these measurements are compared with solution models developed for solubility in systems containing specific solute-solvent interactions. A simple model based on a single 1:1 carbazole:dibutyl ether complex described the solubility data, though the calculated equilibrium constant was about one-half of values published previously. A more sophisticated solution model, which assumes both carbazole:dibutyl ether and carbazole:chloroalkane complexes, was needed to thermodynamically describe the systems studied. Equilibrium constants for three presumed carbazole:chloroalkane complexes are calculated from measured carbazole solubilities.