Dissolution Thermodynamics Research Articles

Equilibrium Solubility of Sulfadiazine in (Acetonitrile + Ethanol) Mixtures: Determination, Correlation, Dissolution Thermodynamics, and Preferential Solvation

The equilibrium solubility of sulfadiazine (SD, 3) in several {acetonitrile (MeCN) + ethanol (EtOH)} mixtures at nine temperatures from T/K = (278.15 K to 318.15) has been determined by following the shake flask method. SD solubility increased with temperature-arising as well as with the MeCN proportion-increasing in the mixtures. Thus, x3 increased from 7.74 × 10−5 in neat EtOH to 6.20 × 10−4 in neat MeCN at T/K = 298.15. SD solubility was adequately correlated with a second-order multivariate equation as function of both mixtures composition and temperature. Moreover, two models including the Jouyban–Acree and Jouyban–Acree–van’t Hoff models were applied to mathematical SD solubility data modeling in solvent mixtures. The accuracy of each model is investigated by the mean relative deviations (MRD%) of the back-calculated solubility. A full predictive model was provided by training the Jouyban–Acree–van’t Hoff model with only seven experimental solubility data which provided excellent predictions with the MRD% of 3.7 %. All used models show a low MRD% values (< 4.0 %) for the calculated data indicating a good correlation of SD solubility data with the given mathematical models. By means of the van’t Hoff and Gibbs equations, the apparent thermodynamic quantities relative to SD dissolution and mixing processes, namely Gibbs energies, enthalpies, and entropies, were calculated and reported. Apparent dissolution quantities of SD were positive in all cases indicating endothermic and entropy-driven behaviors. A non-linear enthalpy–entropy relationship was observed for SD in the plot of SD dissolution enthalpy vs. Gibbs energy. Observed trend exhibits negative slope in the composition from neat EtOH to the mixture of 0.05 in mass fraction of MeCN indicating entropy-driving mechanism for this SD transfer process. Moreover, variant but positive slopes were found in the composition interval of 0.05 < w1 < 1.00 indicating enthalpy-driving mechanism for these SD transfer processes. Furthermore, the preferential solvation of SD by MeCN or EtOH was analyzed by using the inverse Kirkwood–Buff integrals. Thus, SD is preferentially solvated by EtOH molecules in EtOH-rich mixtures but preferentially solvated by MeCN in MeCN-rich mixtures. In this way, this research expands the literature investigations about the solubility of SD in some non-aqueous cosolvent mixtures conformed by MeCN and other alcohols.

A novel process for producing Al-Si alloy utilizing aluminum-silicon oxide extracted from coal fly ash

As a kind of solid waste rich in aluminum and silicon resources, the comprehensive utilization of coal fly ash (CFA) will be of great significance to reduce environmental pollution and improve economic benefits. This work proposed a facile and environmentally friendly cleaning process for producing Al-Si alloy by molten salt electrolysis from CFA extract, aluminum-silicon oxide (ASO). The dissolution behavior and dissolution reaction mechanism of ASO were studied by high temperature visual dissolution experiment, thermodynamics analysis and phase analysis. Due to the chemical reaction between ASO and cryolite-based melt, ASO powder dissolves rapidly in melt and the dissolution rate of ASO is not determined by the phase compositions but by the mass ratio of Al2O3/SiO2. For replenishing the oxide concentration in the electrolyte as quick as possible, the proper mass ratio of Al2O3/SiO2 is in the range of 0.75–7.5. The electrochemical co-reduction behavior of Si (IV) and Al (III) ions on the W electrode was performed by cyclic voltammetry and square wave voltammetry. The results indicated that the reduction of Si (IV) ion in the melt was a two-step irreversible process. Hypoeutectic Al-Si alloy and eutectic Al-Si alloy were prepared by galvanostatic electrolysis using ASO as raw material. This innovative technology can realize high-value recycling of CFA resources and low carbon emission, low energy consumption production of Al-Si alloy.

Dissolution Thermodynamics and Preferential Solvation of Phenothiazine in Some Aqueous Cosolvent Systems

Dissolution Thermodynamics and Preferential Solvation of Phenothiazine in Some Aqueous Cosolvent Systems

Dissolution kinetics and thermodynamics of uranium from a boltwoodite ore for nuclear fuel cycle application

Dissolution kinetics and thermodynamics of uranium from a boltwoodite ore for nuclear fuel cycle application

Effects of calcium and barium chloride salts on the solubility and dissolution thermodynamics of glycine and DL-alanine from 288.15 K to 328.15 K

This investigation primarily examines the solubility at equilibrium and the dissolution thermodynamics of two crucial amino acids, glycine and DL-alanine, in aqueous solutions containing calcium and barium chloride salts. The solubilities were measured from 288.15 K to 328.15 K using the analytical gravimetric method. The resulting solubilities were then used to deduce the thermodynamics of the solutions. Subsequently, the free energies associated with solvation through transfer were examined.Furthermore, the research delved into various thermophysical characteristics within electrolyte solutions in aqueous media, establishing correlations. In addition, this study elucidated various non-covalent processes, including the solubility and stability of amino acids, by considering short-range interactions such as solute–solvent, solvent–solvent, and acid–base interactions. This analysis primarily provides insights into the involved molecular interactions and energetics that govern the solubility and behavior of amino acids in various solution environments.

Inhibition of Vanadium Cathode Dissolution in Zinc‐Ion Batteries on Thermodynamics and Kinetics by Guest Pre‐Intercalation

AbstractAqueous zinc‐ion batteries (AZIBs), recognized for their safety and environmental friendliness, hold significant promise for large‐scale energy storage. However, the rapid capacity degradation resulting from the dissolution of active cathode materials hampers the advancement of AZIBs. Here, Ru0.2V2O5∙0.41H2O (RuVO) is synthesized with remarkable capacity retention (98.2% over 5000 cycles at 10 A g−1). The pre‐intercalation of Ru3+ enhances the stability of both intrinsic and cycling structures, elevating the Gibbs free energy and suppressing V‐dissolution thermodynamically. Additionally, Ru3+ intercalation modulates the potential energy surface of Zn2+ migration, leading to the dominance of Zn2+ in the insertion/extraction mechanism, thereby kinetically impeding the dissolution reaction. This study elucidates the dissolution thermodynamics and kinetics of V‐based cathodes through a combination of experiments, mechanism analyses, and density functional theory (DFT) calculations.

Dissolution thermodynamics and solubility prediction of satranidazole in mono-solvent systems at various temperatures using a single determination

ABSTRACT The reported mole fraction solubility data of satranidazole (SAT) in 18 mono-solvents at five different temperatures (T = 293.2K to 313.2 K) and atmospheric pressure (p = 0.1MPa) collected from the literature were revisited from another physicochemical point of view. The solubility of SAT in 12 mono-solvents was correlated by a newly developed model and six mono-solvents were excluded from correlation due to the non-availability of solvent parameters. Additionally, apparent thermodynamic quantities of dissolution and mixing were calculated based on the van’t Hoff and Gibbs equations by using mole fraction solubilities and reported enthalpy and temperature of fusion of SAT. Results were interpreted in terms of possible intermolecular interactions.

The replies to the comment on “Solubility measurement, correlation, and dissolution thermodynamics of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (2HNIW·HMX) co-crystal in two binary solvent mixtures”

In the published work, the solubility of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane · 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (2HNIW·HMX) co-crystal in two binary solvent mixtures has been reported.

Comments on “Solubility measurement, correlation, and dissolution thermodynamics of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane_1,3,5,7-tetranitro-1,3,5,7-tetrazocane (2HNIW_HMX) co-crystal in two binary solvent mixtures”

The reported solubility 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane_1,3,5,7-tetranitro-1,3,5,7-tetrazocane (2HNIW_HMX) co-crystal in methyl acetate + ethanol/1,2-dichloroethane has been evaluated from viewpoint of the thermodynamic solubility determination and solution stability of co-crystals. The solution stability of the co-crystal is a critical point which should be considered in the determination and calculation of thermodynamic parameters.

Solubility and dissolution thermodynamics of L-histidine and L-tryptophan in aqueous ethanol solution at five equidistant temperatures

This study highlights the saturated solubilities and dissolution thermodynamical properties of two very important amino acids viz. L-histidine and L-tryptophan having various roles in many field in pure aqueous and aqua-ethanol medium at particular as well as range of temperature employing static gravimetric method which is very systematic and error free. Finding confirms that L-histidine shows more solubility in water rich region and L-tryptophan shows more solubility in organic rich region. L-tryptophan has an extra benzene ring which makes L-tryptophan more covalent than L-histidine moiety. Consequently, solubility of former in water rich region becomes low. In connection with those mentioned properties other various physiochemical parameters like co-solvent diameter, apparent dipole moment, apparent molar volume, solvent diameter etc. are also estimated. All observations are explained clearly on the ground of several solution related interactions namely cavity forming, solvent-solvent, solvent-solute interactions etc. Both total and chemical transfer Gibbs energies as well as entropies are calculated and explained to give support to stability and variation of solubility in both aqueous and aqua-ethanol media.

Equilibrium solubility, solvation and dissolution thermodynamics, and density functional theory study of albendazole in solutions of acetone/methanol/isopropanol + water

In this work, albendazole was dissolved in mixtures of acetone/methanol/isopropanol + water to examine its solubility, dissolution thermodynamics, solvation behavior, and intermolecular interactions. The shake-flask method was used to conduct solubility tests at a pressure of 101.0 kPa and temperatures from 278.15 to 323.15 K. In water and pure organic solvents, respectively, the lowest and greatest levels of albendazole solubility were found. XRD analysis-based experiments found no evidence of crystal solvation or transition. Jouyban-Acree, modified Wilson, QSPR and modified van't Hoff-Jouyban-Acree models correlated the solubility to solvent composition and temperature with the relative average deviations (RAD) of no more than 8.99 %. The equilibrium solubility at 298.15 K was examined using the approach of extended Hildebrand solubility parameter, which produced an average relative deviation of 3.63 %. The dipolarity-polarizability and solubility parameter of solutions have a considerable impact on the solubility fluctuation, according to the analysis of linear solvation energy relationship. The preferred solvation of albendazole by water and different organic solvents was quantitatively examined with the help of the inverse Kirkwood-Buff integrals. Albendazole was preferentially solvated by the organic solvents in moderate and rich organic solvent compositions in blends, where albendazole served as a Lewis acid. An enthalpy-driven mechanism and an endothermic process were identified by thermodynamic analysis of the entropy-enthalpy compensation and dissolution properties for albendazole dissolving in blends. The electrostatic characteristics of albendazole acidity/basicity were highlighted using analysis of Hirshfeld surface and molecular surface. The primary targets of nucleophilic and electrophilic assault are the –NH and -S-groups. An independent gradient model based on Hirshfeld partition analysis was used to visual the weak interactions between albendazole and different solvents.

Enhancing the equilibrium solubility of salicylic acid in aqueous media by using polyethylene glycols 200, 400 and 600 as cosolvents: Correlation and dissolution thermodynamics

The solubility of salicylic acid in three mixtures of polyethylene glycol (PEG) with different molar masses of 200 to 600 g/mole were experimentally determined by a shake flask method at temperature range of (293.15 to 313.15) K under ambient pressure (≈85 kPa). The experimental results indicated that the solubility of salicylic acid enhanced by the introduction of PEGs to the water, and that could be explained with Hansen’s parameters and like-dissolves-like rule. Based on the results, PEG 600 had the best solubilization power, whereas PEG 200 displayed the lowest solubilization power, and generally the solubility decreased with decreasing molar mass of PEG and also decreasing temperature. Moreover, the equilibrium solid phase crystal of salicylic acid is characterized with X-ray powder diffraction analysis to identify no polymorphic transformation, solvate formation or crystal transition during the whole solvent crystallization process. A number of linear and nonlinear cosolvency models including the Jouyban-Acree based models along with the equations of van’t Hoff, the mixture response surface, the combined nearly ideal binary solvent/Redlich-Kister, λh and the modified Wilson-van’t Hoff were challenged to correlate/predict the solubility of salicylic acid in these mixtures. The computed values of the Jouyban-Acree based models presented a good agreement with the experiment data than the others, as a consequent of a low mean percentage deviation (MPD ≤ 15.7%). According to the enthalpy–entropy compensation analysis, there observed slope changes indicating that two mechanisms, enthalpy or entropy controlled the solubility increment depending on the PEG mass fraction in each solution.

Equilibrium solubility, solvation and dissolution thermodynamics, and DFT study of 18β-glycyrrhetinic acid in solutions of 1,4-dioxane/N,N-dimethylformamide/ethanol/isopropanol + water

This study investigated the solubility, solvation behavior, dissolution thermodynamics, and intermolecular interactions of 18β-glycyrrhetinic acid (GA) in binary aqueous blends of 1,4-dioxane, N,N-dimethylformamide (DMF), ethanol and isopropanol. The solubility experiments were performed using the shake-flask technique at 101.0 kPa and temperatures ranging from 278.15 to 323.15 K. The lowest and highest GA solubility was observed in water and neat organic solvent, respectively. Experiments based on XRD analysis revealed no crystal transition or solvation. Modified van't Hoff–Jouyban–Acree and Jouyban–Acree models connected the solubility with relative average deviations (RAD) not exceeding 3.63 %. The extended Hildebrand solubility parameter method was utilized here to examine the equilibrium solubility at 298.15 K, yielding a RAD of 3.95 %. According to the linear solvation energy relationship examination, the dipolarity-polarizability and solubility parameter of solutions significantly influence the solubility variation. Using the inverse Kirkwood–Buff integrals, the preferential solvation of GA by organic solvents and water was investigated quantitatively. Positive preferential solvation parameter for organic solvents in rich and moderate organic solvent blends indicated that GA was preferentially solvated by the organic solvents. GA is a Lewis acid with respect to the cosolvent molecules. Thermodynamic investigation of dissolution characteristics and enthalpy–entropy compensation revealed an endothermic process and enthalpy-driven mechanism for dissolving GA in various blends. Finally, microscopic quantitative examination of molecular surface was used to highlight the electrostatic properties of acidity/basicity of GA. The –C = O, OH, and > COOH groups are the main targets of electrophilic and nucleophilic attack. The weak interactions between GA and solvent were visually examined using an independent gradient model based on Hirshfeld partition analysis.

Facet-Dependent Ba Dissolution of Tetragonal BaTiO3 Single Crystal Surfaces

Tetragonal BaTiO3 with a high dielectric property is used as the principal material for multilayer ceramic capacitors (MLCCs), a core component of state-of-the-art electronic devices. However, Ba2+ at BaTiO3 surfaces can be dissolved in aqueous-based media, and such chemical instability has been a major obstacle to environmentally friendly aqueous-based MLCC processes. To understand the behavior of Ba2+ dissolution, we investigated H2O(l) and (H+ + Cl–)(aq.) adsorption on the single crystal surfaces of BaTiO3(100), (111), and (110) using density functional theory calculations. We found that the onset pH for Ba2+ dissolution is 1.65, 2.46, and 3.18 for BaTiO3(100), (111), and (110), respectively, indicating that the thermodynamics of Ba2+ dissolution are facet dependent. The onset pH and the coordination number (CN) of Ba on each surface shows a linear correlation, suggesting that the CN of Ba is a critical factor that can predict the Ba2+ dissolution thermodynamics.

Solubility modeling, dissolution and solvation thermodynamics, and solute–solvent interactions of diflufenican in aqueous aprotic and protic cosolvents

Electrostatic characteristics of acidity and basicity of the diflufenican molecule were uncovered by examining the Hirshfeld surface and the electrostatic potential surface, respectively. When it comes to nucleophilic and electrophilic assault, the >NH, =O, and -O- groups are where it is at. Diflufenican-solvent interactions were shown using an independent gradient model based on Hirshfeld partition analysis. Under 101.2 kPa, the isothermal saturation technique was used to experimentally obtain the diflufenican solubility in mixtures of isopropanol/methanol + water and ethyl acetate + ethanol across the temperature range from 278.15 to 323.15 K. Diflufenican was more soluble in ethyl acetate + ethanol blends than alcohol + water blends at the same temperature and cosolvent composition. Maximum relative average deviation of 9.57 percent was obtained using the Jouyban-Acree and modified van't Hoff-Jouyban-Acree models of correlation. The literature-reported solubility of diflufenican in ethylene glycol (EG), ethanol, propylene glycol (PG), and N,N-dimethylformamide (DMF) + water, as well as our determined in ethyl acetate + ethanol and methanol/isopropanol + water at 298.15 K, were all investigated using an extended Hildebrand solubility parameter approach. The local mole fractions of diflufenican in the seven solutions were also investigated using the inverse Kirkwood-Buff integrals technique. Preferential solvation of diflufenican by PG, ethanol, DMF, methanol, and isopropanol in aqueous solutions and by ethyl acetate in ethyl acetate + ethanol solutions was observed. Diflufenican in aqueous EG mixes was not preferentially solvated by EG. Results and discussion of the enthalpy–entropy compensation features of dissolution were reached.

Solubility measurement, correlation, and dissolution thermodynamics of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane · 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (2HNIW·HMX) co-crystal in two binary solvent mixtures

The solubility of 2HNIW·HMX co-crystal in two binary solvent mixtures (ethanol + methyl acetate, and 1,2-dichloroethane + methyl acetate) was measured by gravimetric method at various temperatures (283.15, 288.15, 293.15, 298.15, 303.15, 308.15, 313.15 and 318.15 K) under atmospheric pressure (0.1 MPa). The experimental results revealed that the solubility for co-crystal in binary solvent mixtures is a simple function of ethanol (or 1,2-dichloroethane) mass fraction and temperature, which decreased with increasing temperature and mass fraction of ethanol (or 1,2-dichloroethane) in the binary solvent mixtures. The solubility of 2HNIW·HMX co-crystal was correlated with the modified Apelblat equation, CNIBS/R-K model, Jouyban-Acree-van't Hoff model, and Jouyban-Acree-Apelblat model. The fitting results demonstrate that the modified Apelblat model and CNIBS/R-K model provided a better correlation with the experimental results than the other models. Furthermore, the van’t Hoff equation was used to study the thermodynamic properties of the 2HNIW·HMX co-crystal dissolution process, including the apparent molar enthalpy change (ΔdisH°), the apparent molar entropy change (ΔdisS°), and the apparent molar Gibbs free energy change (ΔdisG°). The results show that the dissolution of the co-crystal in the selected binary solvent mixture is an exothermic process. The experimental and calculated solubility data and thermodynamic properties of the 2HNIW·HMX co-crystal would be helpful for selecting the appropriate solvent system for the reaction, crystallization, and purification of the 2HNIW·HMX co-crystal.

Effect of N-Methyl-pyrrolidone (NMP) on the Equilibrium Solubility of Meloxicam in Aqueous Media: Correlation, Dissolution Thermodynamics, and Preferential Solvation.

Meloxicam is an analgesic and anti-inflammatory drug widely prescribed in current therapeutics that exhibits very low solubility in water. Thus, this physicochemical property has been studied in N-methyl-pyrrolidone (NMP)–aqueous mixtures at several temperatures to expand the solubility database about pharmaceutical compounds in aqueous–mixed solvents. The flask-shake method and UV–vis spectrophotometry were used for meloxicam solubility determination as a function of temperature and mixture composition. Several cosolvency models, including the Jouyban–Acree model, were challenged for equilibrium solubility correlation and/or prediction. The van’t Hoff and Gibbs equations were employed here to calculate the apparent standard thermodynamic quantities for the dissolution and mixing processes of this drug in these aqueous mixtures. Inverse Kirkwood–Buff integrals were employed to calculate the preferential solvation parameters of meloxicam by NMP in all mixtures. Meloxicam equilibrium solubility increased with increasing temperature, and maximal solubilities were observed in neat NMP at all temperatures. The mole fraction solubility of meloxicam increased from 1.137 × 10–6 in neat water to 3.639 × 10–3 in neat NMP at 298.15 K. The Jouyban–Acree model correlated the meloxicam solubility in these mixtures very well. Dissolution processes were endothermic and entropy-driven in all cases, except in neat water, where nonenthalpy- nor entropy-driven was observed. Apparent Gibbs energies of dissolution varied from 34.35 kJ·mol–1 in pure water to 7.99 kJ·mol–1 in pure NMP at a mean harmonic temperature of 303.0 K. A nonlinear enthalpy–entropy relationship was observed in the plot of dissolution enthalpy vs dissolution Gibbs energy. Meloxicam is preferentially hydrated in water-rich mixtures but preferentially solvated by NMP in the composition interval of 0.16 < x1 < 1.00.

(Digital Presentation) Oxygen Evolution Reaction in Ru1-XMxO2 (M = Ti, Zr, Nb, Ta, Cr) Doped Catalysts: Activity and Stability Effects

The complex reaction mechanisms and dissolution pathways that drive oxygen evolution reaction on metal and metal oxide surfaces under acidic conditions challenge the development of a highly active, highly stable, and low cost catalyst for proton-exchange membrane (PEM) water electrolyzers. Currently, ruthenium-based materials present lower overpotentials, lower cost and higher global supply compared to iridium-based materials, though they are also considerably less stable. In order to elucidate a way to improve RuO2 stability under the harsh conditions during water electrolysis, we use a density functional theory (DFT) approach to investigate the effects on catalyst structure, OER activity and stability of transition metal substitution within Ru1-xMxO2 (M = Ti, Zr, Nb, Ta, Cr) at different atomic concentrations. Calculations show that M substitution within rutile RuO2 affects the electronic structure resulting in regions of electron accumulation and depletion at the surface and shifts the Ru d-band and O2p band centers, which are highly dependent on dopant characteristics and doped site. Moreover, dissolution calculations on the Ru1-xTixO2 surfaces show that Ti substitution alter the metal dissolution pathway energetics and thermodynamics bringing stability to the catalyst in terms of reducing material loss. Theoretical XRD patterns, Ru d-band and O p-band center calculations, and activation and reaction energy trends are in excellent agreement with experimental results that includes X-ray diffraction analysis, high resolution transmission electron microscopy images, X-ray photoelectron spectroscopy of core and valence bands, and rotating disk electrode measurements. In this presentation, we focus on the theoretical and computational aspects. The evaluation of the thermodynamics and kinetics of the water splitting, and oxygen evolution mechanism is done with spin-polarized plane-wave DFT calculations, while Ab Initio Molecular Dynamics (AIMD) simulations allow following and complementing the understanding of the dynamics of the initial steps of water dissociation on the various M and Ru sites. Electronic structure changes on the surface due to the presence of M before and during the reaction are analyzed based on the density of states and local magnetic moments, and the activation energies are obtained from the climbing Nudge Elastic Band method. Dissolution calculations are carried out with constrained-AIMD simulations using the slow-growth approach within the “Bluemoon ensemble” as implemented in VASP.

Dissolution thermodynamics and preferential solvation of genistein in some (ethanol + water) mixtures at different temperatures

The solubility of genistein was measured in the binary system of ethanol and water at temperatures ranging from 288.2 to 328.2 K. The obtained data were correlated with the modified Apelblat model, Yalkowsky model, λh model, CNIBS/R-K model, Jouyban-Acree-van’t Hoff model, and modified Wilson model and their prediction accuracy was evaluated by calculating the mean relative deviation. The thermodynamic functions, Gibbs energy, enthalpy, and entropy of solution were determined using van’t Hoff equation. Moreover, the preferential solvation was analyzed by using the solubility data at 298.2 K. The solubility of genistein in the system increased with an increase in temperature and mole fraction of ethanol in the solvent mixtures. The values for solubility of genistein are ranging from 0.47 obtained in neat water at T = 288.2 K to 5.02 obtained in absolute ethanol at T = 328.2 K. The values of Δ solnG, 0 Δ solnH0 and Δ solnH0 for the dissolution of genistein in mixtures are positive, whereas the values of Δ solnH0 in neat water and absolute ethanol are negative. The thermodynamic properties of dissolution suggest that the dissolution process is non-spontaneous and endergonic. The modified Apelblat model can provide more accurate predictive solubility of genistein in the water and ethanol mixtures, whereas Yalkowsky model calculates solubility of genistein with large deviations. Genistein is preferentially solvated by water in water-rich mixtures (0 < x 2 < 0.24) but preferential solvation by ethanol in the region of 0.24 < x 2 < 1. Overall, this work could be applied for designing and optimizing the extraction, purification, and crystallization process of genistein.

Crystallization Thermodynamics of α-Lactose Monohydrate in Different Solvents.

It is common to find that some of the lactose in dairy powders and pharmaceutical tablets is present in the unstable amorphous state. Therefore, their crystallization thermodynamics in different solvents are particularly important. In this paper, the solubility of α-lactose monohydrate (α-LM) in 15 mono-solvents such as ethanol, isopropanol, methanol, 1-propanol, 1-butanol, 2-butanol, isobutanol, 1-pentanol, isoamylol, 1-hexanol, 1-heptanol, 1-octanol, propanoic acid, acetonitrile, and cyclohexanone was evaluated by using the gravimetric method in the temperature ranges from 274.05 K to 323.05 K at constant pressure (1 atm). In the given temperature range, the solubility of α-LM in these solvents increased with the rising of temperature, the highest solubility of α-LM was found in methanol (2.37 × 104), and the lowest was found in 1-hexanol (0.80 × 105). In addition, the increase of α-LM solubility in isopropanol was the largest. The sequence at 298.15 K was: methanol > 1-butanol > isopropanol > ethanol > 1-propanol > 1-heptanol > isobutanol > propionic acid > 1-pentanol > 1-octanol > acetonitrile > isoamylol > 2-butanol > cyclohexanone > 1-hexanol. Solvent effect analysis shows that the properties of α-LM are more important than those of solvents. The Apelblat equation, λh equation, Wilson model, and NRTL model were used to correlate the experimental values. The root-mean-square deviation (RMSD) and relative average deviation (RAD) of all models were less than 2.68 × 10−2 and 1.41 × 10−6, respectively, implying that the fitted values of four thermodynamic models all agreed well with the experimental values. Moreover, the thermodynamic properties of the dissolution process (i.e., dissolution Gibbs free energy (ΔdisG), molar enthalpy (ΔdisH), and molar entropy (ΔdisS)) for α-LM in selected solvents were determined. The results indicate that ΔdisH/(J/mol) (from 0.2551 to 6.0575) and ΔdisS/(J/mol/K) (from 0.0010 to 0.0207) of α-LM in these solvents are all positive, and the values of ΔdisH and ΔdisS. ΔdisG/(J/mol) (from −0.0184 to −0.6380) are all negative. The values were observed to decrease with rising temperatures, implying that α-LM dissolution is an endothermic, entropy-driven, and spontaneous process. The solid–liquid equilibrium data and dissolution thermodynamics of α-LM were obtained, which provide a basis for industrial production.