Aqueous Ethanol Mixtures Research Articles

Equilibrium solubility of 6-methylcoumarin in some (ethanol + water) mixtures: determination, correlation, thermodynamics and preferential solvation

ABSTRACT The solubility of 6-methylcoumarin in water, ethanol and nine aqueous ethanol mixtures was determined from 293.15 to 323.15 K. 6-Methylcoumarin solubility expressed in mole fraction was correlated with some well-known correlation/prediction models. Gibbs energy, enthalpy and entropy, for dissolution and mixing processes, were computed using van’t Hoff and Gibbs equations. The plot of enthalpy vs. Gibbs energy of dissolution exhibited negative slopes from water to w 1 = 0.20 and from w 1 = 0.90 to ethanol but positive slopes in the interval 0.20 < w 1 < 0.90. 6-Methylcoumarin transfer from water to w 1 = 0.20 is entropy-driven that could be attributed to water molecules releasing originally bounded as ‘icebergs’ around the drug-non-polar groups. In mixtures of 0.20 < w 1 < 0.90, enthalpy-driving mechanism for drug transfer from more-polar to less-polar systems is observed, probably owing to better solvation by ethanol. Inverse Kirkwood–Buff integrals show that 6-methylcoumarin is preferentially solvated by water in water-rich mixtures but preferentially solvated by ethanol in 0.24 < x 1 < 1.00.

Contribution from non-ideality and preferential solvation to non-linear solvatochromism in binary mixtures

The knowledge of preferential solvation is of critical importance in description of the solute behavior in mixed solvents. The analysis of solvatochromic shifts as a function of solvent composition is popular in this regard, since it gives molecular information on solute-solvent interactions. However, due to the complexity of the interactions and possible non-ideality of mixed solvents, implementing an efficient approach for interpretation of solvent-solvent interactions is an opening major challenge in modeling solvatochromism to get reliable results on preferential solvation. Here, we proposed a new methodology to treat solvatochromism in solvent mixtures in order to reach a more reliable picture of the local composition around the solute. As the main idea, the effect of solvent-solvent interactions on spectral shift was considered by formulating the non-ideality of solvent in solvation shell of the solute as a function of the local composition by exploiting the results obtained from the analysis of the bulk mixture non-ideality. From that, the non-linear variation in spectral shift can be well separated into contributions from preferential solvation and the local non-ideality. To test this approach, solvatochroimsm of 2-methyl-4-nitroaniline was studied in some mono-solvents and binary mixtures. The spectral properties of 2-methyl-4-nitroaniline and its response to solvent were rationalized by quantum chemical calculation and linear solvation energy relationships analysis in mono-solvents. Then, the observed strong non-linear solvatochromism of 2-methyl-4-nitroaniline in aqueous mixtures of ethanol, DMF and DMSO was treated by the proposed model that provided both physically and statistically more reliable results on preferential solvation and molecular interactions, with respect to the other widely-used solvent exchange models. As an interesting and important result, non-ideality, but not preferential solvation, was responsible for non-linear solvatochromism in aqueous solutions of ethanol and DMF.

Application of Polarisable Continuum Modelling to assess Minoxidil solubility in mixed solvents

ABSTRACT Experimental solubility of minoxidil was obtained in binary aqueous mixtures of ethanol, methanol and acetonitrile at 298.2 K. The effects of pH and micellisation were investigated on the solubility of the drug. Experimental solubility data was correlated by three co-solvency models, i.e. Yalkowsky, CNIBS/R-K, and the modified Wilson model. Density functional theory and hybrid functional B3LYP method was used with Polarisable Continuum Model (PCM) to correlate the experimental solubility data in various mass fractions of the binary solvent mixtures. We report the results of solute–solvent interaction energy as free energy of solvation (∆G sol ) of minoxidil in various mass fractions of ethanol + water mixtures. Total electrostatic energy, dipole moment, total Gibbs free energy and dielectric constant (ε) of minoxidil were also investigated.

Maximizing the freeze-dried extract yield by considering the solvent retention index: Extraction kinetics and characterization of Moringa oleifera leaves extracts

A complete chemical characterization of Moringa oleifera leaves was carried out showing a high content of extractives. Extraction kinetics of bioactive compounds present in this fraction were performed by conventional and ultrasound assisted extraction (UAE). A 50% (v/v) hydroalcoholic mixture led to the highest total phenolic compounds yield by conventional solvent extraction, 29.5 ± 0.3 mg per gram of moringa leaves. UAE did not bring any improvement when using hydroalcoholic mixtures probably due to the physical properties of the ethanol aqueous mixtures that affect the UAE performance, such as viscosity and vapor pressure of the mixture. The retention index of the different solvents in the raffinate phase was determined revealing the highest retention index for water, 9.5, and a continuous decrease by increasing ethanol concentration. Retention index is a key parameter in a solvent extraction process since it determines the number of stages in an industrial separation process and it is not usually reported in bioactive compounds extraction. Solvent extraction capacity and the retention index determined the final freeze-dried extract yield.

Equilibrium solubility of vanillin in some (ethanol + water) mixtures: determination, correlation, thermodynamics and preferential solvation

Equilibrium mole fraction solubility of vanillin in nine aqueous-ethanolic mixtures, as well as in neat water and neat ethanol, was determined at seven temperatures from T = 293.15 to T = 323.15 K. Vanillin solubility in these mixtures was adequately correlated with several well-known correlation models with the mean percentage deviations of 5.9 to 18.3%. Respective apparent thermodynamic functions, i.e. Gibbs energy, enthalpy, and entropy, for the dissolution, mixing and solvation processes, were computed using the van’t Hoff and Gibbs equations. The enthalpy–entropy relationship for vanillin was non-linear in the plot of enthalpy vs. Gibbs energy of dissolution with positive slopes from neat water to the mixture of w1 = 0.10 and the interval 0.50 < w1 < 0.90 but negative in the interval 0.10 < w1 < 0.50 and from w1 = 0.90 to neat ethanol. Accordingly, in the first cases the vanillin transfer from more polar to less polar solvent systems is enthalpy-driven but entropy-driven for the last ones. Moreover, by means of the inverse Kirkwood-Buff integrals is observed that vanillin is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by ethanol molecules in mixtures of 0.23 < x1 < 1.00.

Imidacloprid (I) in several aqueous co-solvent mixtures: Solubility, solvent effect, solvation thermodynamics and enthalpy–entropy compensation

This contribution dealt with the saturated solubility, solvation behavior, and dissolution and transfer belongings of imidacloprid in some aqueous co-solvent mixtures of n-propanol, acetone, ethanol and methanol by means of experiment and mathematical correlations. Solubility experiments were conducted via a commonly used technique, namely shake-flask method, under 101.2 kPa from 283.15 to 323.15 K. The maxima of the obtained imidacloprid solubility was recorded in neat n-propanol/acetone/ethanol/methanol at temperature T = 323.15 K, which corresponded to 227.7 × 10−5, 2851 × 10−5, 237.9 × 10−5 and 409.9 × 10−5 (mole fraction), respectively; and the minimum, in single water (0.6792 × 10−5 at 283.15 K). The Hansen solubility parameters were used here to illustrate the imidacloprid solubility behavior. Solubility modeling through Jouyban–Acree–van’t Hoff, mixture response surface (MRS), Jouyban–Acree and modified Wilson models achieved the relative average deviations of no higher than 3.01%. As well, the extended Hildebrand solubility approach analyzed the saturated solubility of imidacloprid at 298.15 K attaining the maximum of relative average deviation (RAD) of 1.16%. The key contributions of solution descriptors to the imidacloprid solubility were observed as dipolarity-polarizability and solubility parameter studied through molecular interactions of solvent-solvent and solute-solvent species to the imidacloprid solubility in terms of the linear solvation energy relationships. A quantitatively investigation upon local mole fractions was executed by utilizing the powerful tool of inverse Kirkwood–Buff integrals through considering several properties of solutions. The local mole fractions of n-propanol/acetone/ethanol/methanol were higher than that of the bulk ones in n-propanol/acetone/ethanol/methanol-rich and middle proportions, representing preferential solvation of the imidacloprid by co-solvents (n-propanol/acetone/ethanol/methanol). It is speculated within these regions imidacloprid acts as a Lewis acid with the molecules of co-solvents. Thermodynamic calculation of dissolution properties and enthalpy–entropy compensation study revealed an entropy-driven mechanism and endothermic process of imidacloprid dissolved in blended solvents. Transfer property analysis designated more advantageous solubilization ability over the intermediate and rich-co-solvent contents.

Solubility of coumarin in (ethanol + water) mixtures: Determination, correlation, thermodynamics and preferential solvation

Equilibrium mole fraction solubility of coumarin in nine aqueous-ethanolic mixtures, as well as in neat water and neat ethanol, was determined at seven temperatures from (293.15 to 323.15) K. Coumarin solubility in was adequately correlated with several well-known correlation models with the mean percentage deviations of 5.1–10.8%. The respective apparent thermodynamic functions (Gibbs energy, enthalpy, and entropy) for the dissolution, mixing and solvation processes were computed using the van’t Hoff and Gibbs equations. The enthalpy-entropy relationship for coumarin was non-linear in the plot of enthalpy vs. Gibbs energy of dissolution with negative slope from neat water to the mixture of w1 = 0.10 but positive from this mixture to neat ethanol. Accordingly, in the first case the coumarin transfer from neat water to the mixture of w1 = 0.10 is entropy-driven, which could be attributed to water molecules release originally bounded as “icebergs” around the non-polar groups of this drug. Otherwise, in mixtures of w1 ≥ 0.10 the driving mechanism for the transfer of coumarin from the more polar solvent systems to those less polar is the enthalpy, probably owing the better drug solvation. Moreover, by means of the inverse Kirkwood-Buff integrals is observed that apparently coumarin is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by ethanol molecules in mixtures of 0.23 < x1 < 1.00.

Solubility of trans-resveratrol in {ethanol (1) + water (2)} mixtures revisited: Correlation, dissolution thermodynamics and preferential solvation

ABSTRACT Reported equilibrium mole fraction solubility values of trans-resveratrol in some aqueous-ethanolic mixtures in the temperature interval from (273.2 to 323.2) K were correlated by means of some cosolvency models, like multi-linear models of Jouyban-Acree and Jouyban-Acree-van’t Hoff and non-linear models of the modified Wilson and Buchowski-Ksiazczak. Apparent thermodynamic functions of the dissolution processes were computed using the van’t Hoff and Gibbs equations. Gibbs energy and enthalpy were positive in all cases, while negative and positive entropies were observed. The plot of enthalpy vs. Gibbs energy of dissolution was non-linear with negative slopes in the region of 0.00 ≤ x 1 ≤ 0.60 but positive slope in the region of 0.60 ≤ x 1 ≤ 0.90. Further, by means of the inverse Kirkwood-Buff integrals is observed that trans-resveratrol is preferentially solvated by water in water-rich mixtures but preferentially solvated by ethanol in the composition interval of 0.24 < x 1 < 1.00.

Modelling and Optimization of Ultrasound-Assisted Extraction of Phenolic Compounds from Black Quinoa by Response Surface Methodology.

Phenolic compounds are currently the most investigated class of functional components in quinoa. However, great variability in their content emerged, because of differences in sample intrinsic and extrinsic characteristics; processing-induced factors; as well as extraction procedures applied. This study aimed to optimize phenolic compound extraction conditions in black quinoa seeds by Response Surface Methodology. An ultrasound-assisted extraction was performed with two different mixtures; and the effect of time; temperature; and sample-to-solvent ratio on total phenolic content (TPC) was investigated. Data were fitted to a second-order polynomial model. Multiple regression analysis and analysis of variance were used to determine the fitness of the model and optimal conditions for TPC. Three-dimensional surface plots were generated from the mathematical models. TPC at optimal conditions was 280.25 ± 3.94 mg of Gallic Acid Equivalent (GAE) 100 g−1 dm upon extraction with aqueous methanol/acetone, and 236.37 ± 5.26 mg GAE 100 g−1 dm with aqueous ethanol mixture. The phenolic profile of extracts obtained at optimal conditions was also investigated by HPLC. The two extracting procedures did not show different specificities for phenolic compounds but differed in the extraction yield.

Dehydration – purification of aqueous ethyl alcohol by adsorption over molecular sieves: continuous operation

ABSTRACT Fuel reserves are fast being depleted; hence, alternatives to fossil fuels need to be constantly explored. Ethyl alcohol (ethanol) is an important fuel substitute because it can be blended with the present-day fuels, can be produced via agricultural routes, is comparatively cheap and the technology of production is well known. Fermentation is used to produce dilute (<20 mass %) ethanol, which needs purification. Ethanol forms a minimum boiling azeotrope with water, and hence, advanced distillation methods are employed for purification. Most of these are costly and hence alternative methods of separation are employed: extraction, membrane separation and adsorption. This work has used adsorption for the dehydration – purification of the aqueous mixture of ethanol over various adsorbents. Stainless steel (SS 316 L) column fitted with a sintering plate was employed for adsorption using various adsorbents. Adsorption studies proved that it is possible to obtain high purity (>99.7 mass %) ethanol with molecular sieves. The possibility of continuous operation was successfully demonstrated in this work.

Understanding the Effect of Differently Charged Surfactants on the Protolytic Equilibria of the Drug Naproxen in Micellar Solution

The protonation process of the poorly water-soluble drug naproxen (NAP) was studied potentiometrically in an aqueous cosolvent mixture of ethanol (25% by v/v) at temperature (298.15 ± 0.1) K and an...

Solubility of fluconazole in (ethanol + water) mixtures: Determination, correlation, dissolution thermodynamics and preferential solvation

In this research, the equilibrium mole fraction solubility of fluconazole (FLC) in some aqueous-ethanolic mixtures was determined at seven temperatures from (293.15 to 323.15) K. The respective apparent thermodynamic functions (Gibbs energy, enthalpy, and entropy) for the dissolution, mixing and solvation processes were computed using the van’t Hoff and Gibbs equations. The enthalpy–entropy relationship for FLC was non-linear in the plot of enthalpy vs. Gibbs energy of solution with negative slope in the composition regions of 0.00 ≤ w1 ≤ 0.40 and 0.70 ≤ w1 ≤ 1.00. Thus, the driving mechanism for FLC transfer processes in water-rich mixtures is the entropy. In addition, by means of the inverse Kirkwood-Buff integrals is observed that FLC is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by ethanol molecules in the mixtures of 0.23 < x1 < 1.00.

Solubility and dissolution thermodynamics of 5-fluorouracil in (ethanol + water) mixtures

Equilibrium mole fraction solubility of 5-fluorouracil (5-FU) in 19 aqueous-ethanolic mixtures, as well as in neat water and neat ethanol, was determined at seven temperatures from (293.15 to 323.15) K. 5-FU solubility in these mixtures was adequately correlated with several well-known correlation models. The respective apparent thermodynamic functions (Gibbs energy, enthalpy, and entropy) for the dissolution, mixing and solvation processes were computed using the van’t Hoff and Gibbs equations. The enthalpy–entropy relationship for 5-FU was non-linear in the plot of enthalpy vs. Gibbs energy of solution with variant but positive slope in almost all the composition regions. Thus, the driving mechanism for 5-FU transfer processes was the enthalpy. In addition, by means of the inverse Kirkwood-Buff integrals is observed that apparently 5-FU is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by ethanol molecules in ethanol-rich mixtures.

Solubility, dissolution thermodynamics and preferential solvation of 4-nitroaniline in (ethanol + water) mixtures

ABSTRACT In this research, the equilibrium mole fraction solubility of 4-nitroaniline (4-NA) in some aqueous-ethanolic mixtures was determined at seven temperatures from (293.15 to 323.15) K. The respective apparent thermodynamic functions (Gibbs energy, enthalpy, and entropy) of the dissolution processes were computed using the van’t Hoff and Gibbs equations. The enthalpy-entropy relationship for 4-NA was non-linear in the plot of enthalpy vs. Gibbs energy of solution with negative slopes from neat water to the mixture w 1 = 0.10 and from w 1 = 0.20 to neat ethanol but positive slope from w 1 = 0.10 to w 1 = 0.20. Therefore, the driving mechanism for 4-NA transfer processes is the entropy in water-rich mixtures. Additionally, by means of the inverse Kirkwood-Buff integrals is observed that 4-NA is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by ethanol molecules in the mixtures of 0.23 ≤ x 1 ≤ 1.00.

Dissolution thermodynamics and preferential solvation of 2,4-dinitrotoluene in (ethanol + water) mixtures

In this research, the equilibrium mole fraction solubility of 2,4-dinitrotoluene (2,4-DNT) in some aqueous-ethanolic mixtures was determined at seven temperatures from (293.15 to 323.15) K. The respective apparent thermodynamic functions (Gibbs energy, enthalpy, and entropy of the dissolution processes) were computed using the van't Hoff and Gibbs equations. The enthalpy-entropy relationship for 2,4-DNT was non-linear in the plot of enthalpy vs. Gibbs energy of solution with negative slope in the composition region 0.00 ≤ w1 ≤ 0.40 but positive slope in the region 0.40 ≤ w1 ≤ 1.00. Therefore, the driving mechanism for 2,4-DNT transfer processes is the entropy in water-rich mixtures and the enthalpy in ethanol-rich mixtures. In addition, by means of the inverse Kirkwood-Buff integrals is observed that 2,4-DNT is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by ethanol molecules in the mixtures of 0.23 ≤ x1 ≤ 1.00.

Evodiamine in several binary aqueous co-solvents: Solubility measurement and modeling, Hansen solubility parameter, preferential solvation and apparent dissolution and transfer properties

Equilibrium solubilities of evodiamine were determined in four aqueous mixtures of methanol, isopropanol, acetone and ethanol over their full mass fraction range via the shake-flask approach covering from 283.15 to 323.15 K. The solubility profiles showed maxima in the neat cosolvents. The temperature and the mixture composition dependence of evodiamine solubility in mole fraction scale was well described by using five well-known models involving NRTL, Jouyban-Acree, van't Hoff-Jouyban-Acree, UNIQUAC and Wilson. The means of the relative deviations were recorded as 5.40%, 0.98% and 0.48% for the Wilson, UNIQUAC and NRTL models, respectively. The Jouyban-Acree and van't Hoff-Jouyban-Acree models resulted in the calculated relative average and root-mean-square deviations lower than 6.83% and 9.19 × 10−6, respectively. Hansen solubility parameter was utilized to disclose the solubility behavior of evodiamine. We also employed the linear solvation energy relationships to detect which intermolecular interactions were mainly responsible for the observed solvent effect upon solubility behavior. This analysis revealed the highlighted role of cavity term and dipolarity-polarizability of solvent in solubility variation of evodiamine. Solubility data was further examined by using the inverse Kirkwood-Buff integrals method in order to analysis the preferential solvation of evodiamine in the mixtures. Results showed the selective solvation of evodiamine by organic solvent in intermediate and organic solvent-rich compositions, and by water in water-rich compositions. The thermodynamic quantities including the apparent molar dissolution enthalpy, molar dissolution entropy and molar Gibbs energy, and the relative contribution of dissolution enthalpy and dissolution entropy to the dissolution Gibbs energy change for dissolution of evodiamine were calculated in each binary mixture. Moreover, the transfer properties were derived and discussed.

Розроблення технологічної схеми екстракції коренів Carlina acaulis

Розроблено технологічні схеми одержання екстрактів коренів Carlina acaulis, які дали змогу отримувати вторинні метаболіти лікарських рослин для виробництва фармацевтичних препаратів. Carlina acaulis є лікарською рослиною, яка нині є недостатньо вивченою. Відомо, що корені містять дубильні та смолисті речовини, інулін (12-18 %), барвники, ефірну олію (1-2 %) та цукор. Встановлено, що для максимального вилучення фенольних сполук і флавоноїдів потрібно правильно підібрати ефективну технологію екстрагування. Розроблено на підставі кінетичних закономірностей екстрагування технологічні схеми двома способами – настоюванням та настоюванням з перемішуванням в апараті з мішалкою. Запропоновано як екстрагент використати 70 % водно-етанольну суміш, співвідношення сировина: екстрагент – 1:10, розмір частинок 2 мм. Встановлено, що час екстрагування методом настоювання становить 48 год, методом настоювання з перемішуванням – 3 години. Отримано настоянку в'язкої консистенції, світло-коричневого кольору із вмістом етанолу не більше 15 %, сухим залишком не менше 70 % і також перевірено на мікробіологічну чистоту. Технологічна схема виробництва містить підготовку рослинної сировини (подрібнення, просіювання, зважування), отримання первинної витяжки (мацерація) та фільтрування й освітлення настоянки (очищення від баластних речовин способом охолодження, відстоювання, фільтрування та ін.). Зроблено висновок, що на підставі розроблених технологічних схем можна отримувати екстракти C. acaulis з максимальним виходом фенольних сполук та флавоноїдів. Одержані настоянки мають високі органолептичні та фізико-хімічні показники та можуть застосовуватись як лікарський засіб.

HPLC determination of phenolic compounds in different solvent extracts of mulberry leaves and antioxidant capacity of extracts

ABSTRACT The antioxidant activities and phenolic contents of mulberry leave extracts obtained by aqueous mixture of acetone, ethanol and methanol were determined. Both alkaline hydrolysis and acid hydrolysis were used to extract bound phenolics. HPLC was used to determine the profile of the extracted phenolics. Three experimental assays, namely, Fe3+ reducing antioxidant power (FRAP), ABTS- and DPPH-radical scavenging activity, were employed to characterize their antioxidant activity. This indicates that acetone was the most effective solvent for extracting free phenolics from mulberry leaves, and the acetone extract exhibited the highest antioxidant capacity. In addition, alkaline hydrolysis was found to be the most efficient method for extracting bound phenolics and produced an extract with better antioxidant properties compared to acid hydrolysis.

Catalytic Properties of ZnLaZrSi-Oxide Systems in the Process of Obtaining 1,3-Butadiene from Ethanol–Aqueous Mixtures

The catalytic properties of ZnLaZrSi-oxide systems prepared on the basis of different types of silica (SBA-15, MCM-41, MCM-48, MCF, large-pore silica, Aerosil A-175) in the process of obtaining 1,3-butadiene (BD) from ethanol–aqueous mixtures were studied. It has been determined that the porous structure characteristics are not critical parameters for achieving high selectivity and yield of BD. The activity and selectivity of catalysts depends on the acid–base properties of their surface, which are determined by the type of silica. High values of selectivity for BD are achieved in the presence of catalysts based on KSKG silica (SBD = 65-68%) and SBA-15 (SBD = 63%).

Solubilisation of dexamethasone: experimental data, co-solvency and Polarised Continuum Modelling

ABSTRACT Experimental solubility of dexamethasone was obtained in binary aqueous mixtures of ethanol, methanol and acetonitrile at 298.2 K. The effects of micellization and pH were also investigated on the solubility of the drug. Experimental solubility data in the binary solvent mixtures were correlated by three co-solvency models, i.e. Yalkowsky, CNIBS/R-K, and the modified Wilson model. A new principle has also been investigated with the purpose of modelling drug solubility in the binary solvent mixtures using Polarised Continuum Model (PCM) by using the hybrid functional B3LYP method and 6–311++G** basis set. By matching experimental data with PCM modelling, we investigated the outcome of drug solubility in various mass fractions of binary solvent mixtures. Here we report the solute-solvent interaction energy as free energy of solvation (∆Gsol), total electrostatic energy, dipole moment, total Gibbs-free energy and dielectric constant (ε) of dexamethasone in various mass fractions of ethanol + water mixtures.