Volumetric Properties of Glycerol Formal + Propylene Glycol Mixtures at Several Temperatures and Correlation with the Jouyban–Acree Model

Molar volumes, excess molar volumes, and partial molar volumes were investigated for glycerol formal + propylene glycol mixtures from density measurements at temperatures from (278.15 to 313.15) K. Mixture compositions were varied in 0.05 in mass fraction of both components. Excess molar volumes were fitted to the Redlich?CKister equation and compared with literature values for other systems. The system exhibits positive excess volumes probably due to increased non-specific interactions. The effect of temperature on the different volumetric properties studied was also analyzed. In addition, the volumetric thermal expansion coefficients were calculated. The Jouyban?CAcree model was used for density and molar volume correlations of the mixtures at the different experimental temperatures. The mean relative deviations between experimental and calculated data are 0.04±0.03 and 0.04 ±0.05, respectively, for the density and molar volumes, using the minimum number of data points, the Jouyban?CAcree model can predict density and molar volume with acceptable accuracies (0.06±0.04 and 0.08±0.05, respectively).     

Solubility and Solution Thermodynamics of Some Sulfonamides in 1-Propanol + Water Mixtures

The solubilities of sulfadiazine (SD), sulfamerazine (SMR) and sulfamethazine (SMT) in some 1-propanol + water co-solvent mixtures were measured at five temperatures from 293.15 to 313.15 K over the polarity range provided by the aqueous solvent mixtures. The mole fraction solubility of all these sulfonamides was maximal in the 0.80 mass fraction of 1-propanol solvent mixture (δ _solv = 28.3 MPa^1/2) and minimal in water (δ = 47.8 MPa^1/2) at all temperatures studied. The apparent thermodynamic functions Gibbs energy, enthalpy, and entropy of solution were obtained from these solubility data by using the van’t Hoff and Gibbs equations. Apparent thermodynamic quantities of mixing were also calculated by using the ideal solubilities reported in the literature. Nonlinear enthalpy–entropy relationships were observed for these drugs in the plots of enthalpy versus Gibbs energy of mixing. The plot of ?_mix H° versus ?_mix G° shows different trends according to the slopes obtained when the mixture compositions change. Accordingly, the mechanism for the solution process of SD and SMT in water-rich mixtures is enthalpy driven, whereas it is entropy driven for SMR. In a different way, in 1-propanol-rich mixtures the mechanism is enthalpy driven for SD and SMR and entropy driven for SMT. Ultimately, in almost all of the intermediate compositions, the mechanism is enthalpy driven. Nevertheless, the molecular events involved in the solution processes remain unclear.     

Solubility of Genistin in Ethanol/Acetone + Water and Daidzein in Ethanol + Water Co-solvent Mixtures Revisited: IBKI Preferential Solvation Method

The preferential solvation parameters (δx_1,3) of genistin in ethanol/acetone (1) + water (2) and daidzein in ethanol (1) + water (2) co-solvent mixtures at elevated temperatures were derived from available solubility data using the inverse Kirkwood–Buff integral method. The values of δx_1,3 varied non-linearly with the co-solvent (1) proportion in all the aqueous mixtures. For the three co-solvent mixtures, the values of δx_1,3 were negative in water-rich mixtures, which indicated that daidzein or genistin was preferentially solvated by water and can act as Lewis bases to establish hydrogen bonds with the proton-donor functional groups of water (1). The same behavior was also observed for daidzein in ethanol (1) + water (2) and acetone (1) + water (2) mixtures with co-solvent-rich composition. For daidzein in ethanol (1) + water (2) mixtures with composition 0.24 < x₁ < 1, and genistin in ethanol (1) + water (2) and acetone (1) + water (2) mixtures with intermediate compositions, the local mole fractions of ethanol or acetone were higher than those of the mixtures and therefore the δx_1,3 values were positive, which indicated that genistin and daidzein were preferentially solvated by the co-solvent. In these regions, daidzein and genistin were acting as a Lewis acid with ethanol or acetone molecules.     

Solution Thermodynamics of Ethylhexyl Triazone in Some Ethanol + Ethyl Acetate Mixtures

Ethylhexyl triazone (EHT) is a sunscreen agent that is widely used in skin care product formulations, whose physicochemical properties have not been previously studied in detail. For this reason, solubility data were measured for EHT in ethanol (EtOH) + ethyl acetate (AcOEt) mixtures at five temperatures. By using the van’t Hoff and Gibbs equations, the thermodynamic functions: Gibbs energy, enthalpy, and entropy of solution, and of mixing, were evaluated from these solubilities. The solubility is greatest in mixtures with 0.10 and 0.20 mass fraction EtOH, but decrease as the EtOH mass fraction increases in the solvent mixtures. By means of an enthalpy-entropy compensation analysis, a nonlinear DH_soln⁰\Delta H_{\mathrm{soln}}^{0} versus DG_soln⁰\Delta G_{\mathrm{soln}}^{0} compensation plot was obtained having both negative and positive slopes as the solvent composition was varied. Accordingly to these results, it follows that the driving function for solubility of EHT is the entropy for solutions rich in EtOH or AcOEt, whereas in mixtures of medium composition, the driving function is the enthalpy.     

“Exclusion Zone” Formation in Mixtures of Ethanol and Water

Brownian particles suspended in water or other polar liquids are pushed out of the region next to hydrophilic polymers, leaving a microsphere-free region known as the “exclusion zone” (EZ). This study aimed to test the hypothesis that the dilution of ethanol in water may influence EZ formation. EZs were created in aqueous media using Nafion tubes as EZ-nucleating surfaces. To define the outer edge of the EZ, carboxylate microspheres, 1 µm diameter, were used. Dynamic movement of microspheres away from Nafion surface was registered in mixtures of ethanol and water, the ethanol concentration varying from 0 to 95%. We found that mixtures with the highest concentrations of ethanol generally produced the smallest EZs and the slowest EZ buildup. However, an unexpected result was the presence of an extremum corresponding to ~10% ethanol. At this concentration, the EZ is larger than in either pure water or almost pure ethanol.     

Study of Malachite Green Fading in Water–Ethanol–Ethylene Glycol Ternary Mixtures

The rate constant of malachite green (MG⁺) alkaline fading was measured in water–ethanol–ethylene glycol ternary mixtures. This reaction was studied under pseudo-first-order conditions at 283–303 K. In each series of experiments, the concentration of ethanol was kept constant and the concentration of ethylene glycol was changed. It was shown that due to hydrogen bonding and hydrophobic interaction between MG⁺ and alcohol molecules the observed reaction rate constant, $ k_{\text{obs}} $ , increased in the water–ethanol–ethylene glycol ternary mixtures. The fundamental rate constants of MG⁺ fading in these solutions ( $ k_{1} $ , $ k_{ - 1} $ and $ k_{2} $ ) were obtained by the SESMORTAC model. Analysis of $ k_{1} $ and $ k_{2} $ values in solutions containing constant ethanol concentrations show that in low concentrations of ethylene glycol, hydrogen bonding formed between ethanol and ethylene glycol molecules and in high concentrations of ethylene glycol, ethanol as a solvent for ethylene glycol affected the reaction rate.     

Equations for the Partition of Neutral Molecules, Ions and Ionic Species from Water to Water–Ethanol Mixtures

Equations set up for the transfer of neutral solutes from water to water?Cethanol mixtures can also be used to correlate the transfer of ions and ionic species, as log₁₀ P, where P is the partition coefficient. Only two additional terms are required in the equations, one for anions and one for cations. The extended equations can fit log₁₀ P values for anions and cations with a standard deviation of about 0.2 to 0.3 log units for transfer of 41 anions and cations from water to various water?Cethanol mixtures from 10?% ethanol to 100?% ethanol by volume. The log₁₀ P values for carboxylate anions and protonated amine cations as obtained from the variation of pK _a with solvent are quite compatible with log₁₀ P values for simple anions and cations.     

Solubility of Adenine and Kinetin in Water–Ethanol Solutions

We have measured the solubility of adenine and kinetin in water–ethanol solutions. Various models of cosolvency have been taken into account in the analysis of the experimental data. The results are interpreted in terms of hydrophobic interactions.     

Solubility of Atrazine in Binary Mixtures of Water + Ethanol or 1-Propanol from 283.15 to 343.15 K

The solubility of atrazine (solid) was measured in water + ethanol and water + propanol from 283.15 to 343.15 K. The experimental results showed that in ethanol + water and 1-propanol + water the solubility of atrazine increased slowly with temperature below 308.15 K but increased significantly above 308.15 K. It was also found that the slope of the solubility–temperature curve increases significantly with an increase in the mole fraction of organic solvent in the mixtures. The modified Apelblat and NRTL equations were applied to describe the measured systems. The model parameters of the NRTL equation were expressed as a function of temperature.     

Thermodynamics of Mixing and Solvation of Ibuprofen and Naproxen in Propylene Glycol + Water Cosolvent Mixtures

By using the van’t Hoff and Gibbs equations, solubility data of ibuprofen (IBP) and naproxen (NAP) determined at several temperatures in propylene glycol (PG) + water (W) cosolvent mixtures were used to evaluate the Gibbs energies, enthalpies, and entropies of solution, mixing and solvation. The solubilities are greater in pure PG and lower in W in both cases at all studied temperatures. These results clearly show that a cosolvent effect is present in these systems. The solvation of these drugs was greater in W compared to PG, and it was lower in the cosolvent mixtures compared with the pure solvents. By means of an enthalpy-entropy compensation analysis, non-linear ΔH _soln^o versus ΔG _soln^o compensation plots were obtained, with negative and positive slopes if all of the composition intervals are considered. Accordingly, it follows that at low PG solvent fractions the dominant factor for the solubility of IBP and NAP in this cosolvent system is the entropy, probably due to loosening of the water structure caused by the addition of the cosolvent.     

Study of Solvent Effects on the Protonation of Functional Group of Disubstituted Anilines: Factor Analysis Applied to the Correlation between Protonation Constants and Solvatochromic Parameters in Ethanol–Water Mixtures

Summary. The stoichiometric protonation constants (log β) of some disubstituted aniline derivatives in ethanol–water mixtures (0–90% ethanol by volume) at 25.0 ± 0.1°C were firstly submitted to factor analysis in order to obtain the number factors which affect the variation of the whole data sets and, afterwards, submitted to target factor analysis to identify these factors. The influence of solvatochromic parameters in the interactions between aniline derivatives and the solvent studied was identified and quantified. The general equation of Kamlet and Taft was reduced for these mixtures to two terms using combined factor analysis (FA) and target factor analysis (TFA): the independent term and the hydrogen-bond donating ability, α (HBD), solvatochromic parameters. Further, the quasi-lattice quasi-chemical (QLQC) theory of preferential solvation has been applied to quantify the preferential solvation by water of electrolytes in ethanol–water mixtures. The effects of the substituents on the protonation constants, the additivities of these effects, and the applicability of the Hammett equation to the behavior of substituents are also discussed. Further, Hammett’s reaction constant for the protonation of disubstituted anilines has been obtained for all the solvent mixtures and correlates well with α (HBD) of the solvent.     

Solubility and Dissolution Thermodynamics of Cefmetazole Acid in Four Neat Solvents and Preferential Solvation in Co-Solvent Mixtures of (Methanol,Ethanol or Isopropanol) + Water

The solubilities of cefmetazole acid in methanol, ethanol, isopropanol and water were determined experimentally by using the saturation shake-flask method within the temperature range from (278.15 to 303.15) K under pressure p?=?101.1 kPa. At a fixed temperature, the cefmetazole acid solubility falls in the order methanol?>?ethanol?>?isopropanol?>?water. The apparent dissolution enthalpy, dissolution entropy and Gibbs energy change were calculated. The acquired solubilities were correlated with Apelblat’s equation. The largest value of relative average deviation for mole fraction solubility was 0.45 × 10^?2, and of root-mean-square deviation, 0.747 × 10^?5. The type and extent and direction of solute–solvent interactions were identified using the concept of Linear Solvation Energy Relationship. In addition, the preferential solvation parameters (δx_1,3) of cefmetazole acid in co-solvent mixtures of methanol (1)?+?water (2), ethanol (1)?+?water (2) and isopropanol (1)?+?water (2) were derived via the inverse Kirkwood–Buff integrals method. At 298.15 K, the magnitude of preferential solvation of cefmetazole acid by the co-solvent is highest in methanol mixtures, followed by ethanol mixtures, and finally by isopropanol mixtures.     

Composition of Surface Layer at the Water–Air Interface and Micelles of Triton X-100 + Rhamnolipid Mixtures

Measurements of the surface tensions, densities and viscosities of aqueous solutions of Triton X-100 (TX-100) and rhamnolipid (RL) mixtures, at constant concentration of RL or TX-100, were carried out. The measured values of the surface tension were compared to those determined using different theoretical models and on the basis of the surface tension of aqueous solutions of individual surfactants. From the surface tension isotherms, the Gibbs surface excess concentration of TX-100 and RL, the composition of surface layer and the standard Gibbs free energy of adsorption at the water–air interface were determined. Moreover, on the basis of surface tension, density and viscosity isotherms, the CMC of surfactants mixtures were evaluated. From the density isotherms, apparent and partial molar volumes of TX-100 and RL were also determined. These volumes were compared to those calculated from the sizes of TX-100 and RL molecules. There was observed a synergetic effect in the reduction of water surface tension and micelle formation, which was confirmed by the intermolecular interactions parameter. In the case of micelle formation, this effect was discussed based on the standard Gibbs free energy of micellization as well as of TX-100 and RL mixing in the micelles. The synergism of TX-100 and RL mixtures in the reduction of water surface tension and micelle formation was explained on the basis of electrostatic interactions between the hydrophilic part of TX-100 and RL molecules; this was supported by pH measurements.     

Activity Coefficients of Sodium Chloride in Water–Ethanol Mixtures: A Comparative Study of Pitzer and Pitzer–Simonson Models

Activity coefficients of NaCl were determined in water–ethanol solvents, in the range 5–20% (w/w) ethanol, from emf data. The molalities varied from 0.1 mol-kg^-1 to near saturation and measurements were taken in the temperature range 25–50°C. The Pitzer model was used to describe the nonideal behavior of the electrolyte and the corresponding coefficients were determined for each solvent. The Pitzer–Simonson equations were also applied and a detailed study, involving the short- and long-range forces, was done in order to better understand the different results obtained with both models.     

Molecular Organization of Reagents in the Kinetics and Catalysis of Liquid-Phase Reactions: XI. Manifestation of the Structure of Solution in the Kinetics of Water Addition to Isocyanate in Water–Dioxane Mixtures

Evidence for the structural effect of liquids associated by hydrogen bonds on the kinetics of molecular reactions was experimentally found. The kinetics of hydrolysis of (phenylaza)phenyl isocyanate in water–dioxane mixtures was studied at various temperatures and in the presence of structure-making and structure-breaking additives. The apparent order of reaction with respect to water concentration increased with temperature because of the partial breaking of the H-bond solution structure. It was found that the value of was affected by salt additives, for which positive (Et₄NCl) or negative (KI) hydration is typical. This hydration resulted in strengthening or partially breaking the H-bond structure of water, respectively. It follows from the kinetic data that the addition of 0.1 mol/l Et₄NCl was equivalent to a decrease in the solution temperature by 6 to 7°, whereas the addition of 0.1 mol/l KI was equivalent to an increase in the temperature by 5 to 6°. The effect of poly(ethylene oxide) additives (which stabilize the structure of water) on the value of was similar to the effect of the tetraethylammonium salt, which is characterized by positive hydration.     

Complex Formation of Crown Ethers with Cations in Water–Organic Solvent Mixtures. Part IV. Thermodynamics of Interaction of Na+ Ion with Benzo-15-crown-5 Ether in the Mixtures of Water with Acetonitrile at 298.15 K

The equilibrium constants of complex formation of benzo-15-crown-5 ether with sodium ion have been determined by molar conductance at various molar ratios of benzo- 15-crown-5 ether and sodium iodide in mixtures of water with acetonitrile at 298.15 K. The thermodynamic quantities of complex formation of benzo-15-crown-5 ether with sodium cation are calculated. The enthalpy of solvation of benzo-15-crown-5 ether and sodium ion complex is discussed together with solvation enthalpies of the cation and ligand. The contribution of the benzene ring to the thermodynamic properties of complex formation and to the enthalpy of solvation of the crown ether/ Na⁺ complex in the mixtures of water with acetonitrile are analyzed and discussed.     

A Correlation Between Solvatochromic Solvent Polarity Parameters and the Ionization Constants of Various Phenols in 1,4-Dioxane–Water Mixtures

Precise thermodynamic ionization constants K for 3-nitrophenol, 3,4-dichlorophenol, and 4-cyanophenol have been obtained in 1,4-dioxane-water mixtures (0–70% volume fraction in dioxane) at 25°C using a potentiometric method. The same information for another twelve cationic, neutral, and anionic phenols were taken from the literature. Three different methods were used to study the effects of the solvents on the ionization constants: one involves a single polarity parameter, E _T(30); the next involves the Kamlet–Taft multiparametric method; and the last involves the preferential solvation model. The pK values follow the preferential solvation model, but the parameters obtained are highly correlated. Using the data for the phenol molecule as reference, a linear correlation between ΔpK and E _T(30) has been used to develop a new method of obtaining pK values for any binary solvent composition, with only the pK in water known. The pK(s) values correlate with the molecular parameters for the dipolarity/polarizability of the solvent π* and its hydrogen-bond donor ability α. The preferential solvation parameter, f _12/1, correlates with the parameter for the hydrogen-bond donor ability of the solvent. All the phenols follow Hammett's equation and the reaction constants have been calculated for the different water–dioxane mixtures.