Equilibrium Mole Fraction Research Articles

Determination of morphine sulfate anti-pain drug solubility in supercritical CO2 with machine learning method

Accurate solute solubility measuring and modeling in supercritical carbon dioxide (ScCO2) would address the best working conditions and thermodynamic boundaries for material processing with this type of fluid. Theory- and data-driven methods are two general modeling approaches. Using theory-driven methods, the solubility is estimated based on the principles of thermodynamics, while data-driven methods are developed by training the algorithms. Despite acceptance of each of these methods, more experimental solubility data are still needed to promote modeling performances. In this study, for the first time, solubility of morphine sulfate is determined and modeled by a set of 13 semi-empirical (theory-driven) and random forest (data-driven) models. Using a laboratory system with an ultraviolet-visible (UV-Vis) spectroscopy, the experimental solubilities including 48 data points were obtained at different temperatures (308–338 K) and pressures (12–27 MPa). The minimum (0.806 × 10−5) and maximum (5.902 × 10−5) equilibrium mole fractions were observed at working pressures of 12 and 27 MPa, respectively, both at the same temperature of 338 K. It was indicated that random forest model (with AARD% of 1.29%) had an excellent predictive performance against semi-empirical models (with AARD% from 9.33 to 19.76%). The results showed that solute molecular weight had the highest effect on random forest modeling. Using modeling results from Chrastil and Bartle models, total and vaporization enthalpies of dissolution of morphine sulfate in ScCO2 were found to be 35.12 and 59.04 kJ/mole, respectively.

Study on Explosion Mechanism of Dimethyl Ether/H2-Blended Gas Based on Chemical Kinetics Method

In order to reveal the deflagration mechanism of DME/H2-blended gasses, the micro-mechanism was studied based on the constructed UC San Diego 2016 pyrolysis oxidation mechanism model. The results show that adiabatic flame temperature and laminar flame speed increase with the increase in the equivalence ratio (Φ); they first increase and then decrease with the increase in the hydrogen (H2)-blended ratio (λ), and with the increase in λ, the Φ corresponding to the peak laminar flame speed of the blended gas increases. The addition of H2 increases the consumption of O2, and H2 reacts with CO to form H2O and CO2, promoting complete combustion. When Φ = 1.0–1.2, the equilibrium mole fraction of H and OH-activated radicals reach the maximum, and with the addition of H2, the concentration of activating radicals gradually increases, while the number of promoted elementary reactions increases by two, and the number of inhibited elementary reactions does not increase. Meanwhile, the addition of H2 increases the reaction rate of most reactions on the main chemical reaction path CH3OCH3→CH3OCH2→CH2O→HCO→CO→CO2 of DME and increases the risk of the deflagration of DME/H2-blended gas.

Solubility of sildenafil citrate in acetonitrile + water mixture at different temperatures

ABSTRACT The study involved the determination of the equilibrium mole fraction solubility of sildenafil citrate in aqueous binary mixtures of acetonitrile across a range of temperatures (from 293.15 K to 313.15 K). To represent this data numerically, both linear and non-linear cosolvency models were employed, and their performances were assessed through mean relative deviations or MRD%. Additionally, this study calculated the apparent thermodynamic properties (Gibbs energy, entropy, and enthalpy) for the dissolution processes using the van’t Hoff and Gibbs equations. Moreover, the study determined the density values of sildenafil citrate saturated solutions and presented them through the van’t Hoff equation.

Thermodynamic consideration of dissolution and distribution behavior of carvedilol in pharmaceutical significant media

The key physico-chemical properties for pharmaceutical design as solubility and distribution coefficients of cardiovascular carvedilol (CVD) in modeling solvents and biphasic systems were determined using the classic shake flask method in the temperature range (293.15–313.15) K. The drug solubility in 1-octanol and hexane was measured at first time. The equilibrium mole fraction solubility of CVD at reference temperature was changed in following order: 1-octanol (2.79∙10-3) > hexane (4.56∙10-6) > buffer pH 2.0 (3.39∙10-6) > buffer pH 7.4 (1.53∙10-7). Solubility pH-profile was characterized a weak solubility in acidic media and very poor solubility in neutral. The experimental lipophilic values logDO/B (1.83 and 2.36 at buffer solution pH 2.0 and 7.4, respectively) were shown the excellent penetration power into both the circulatory system and the entire intestinal tract. The temperature dependences of the CVD distribution coefficients in 1-octanol/buffer and hexane/buffer two-phase systems at pH two values (2.0 and 7.4) were considered from the thermodynamic view point. Thermodynamic functions of solubility and transfer processes were calculated and analyzed. Thermophysical parameters of the compound were used for estimation of the ideal solubility and activity coefficients. Moreover partial excess thermodynamic functions of CVD dissolution in saturated solutions, demonstrating the positive deviation real solvents from ideality, are also evaluated in detail. The data obtained will be in demand both for the creation of conceptually new dosage forms of carvedilol with improved bioavailability, and for constructing structure–property correlations in a number of structure-like compounds.

Study on 2-amino-4-chloro-6-methoxypyrimidine in four binary solvent mixtures: Solubility measurement, calculation, preferential solvation and extended Hildebrand solubility parameter approach analysis

Equilibrium mole fraction solubility of 2-amino-4-chloro-6-methoxypyrimidine in methanol/ethanol/acetone/N,N-Dimethylformamide (DMF) plus water was experimentally measured by isothermal saturation method at 278.15–323.15 K under 101.2 kPa. The mixed solvents with low moisture and high temperature played a supportive role in the dissolution of 2-amino-4-chloro-6-methoxypyrimidine. The amount of 2-amino-4-chloro-6-methoxypyrimidine dissolved in DMF + water was more than that in other three systems and the ranges of values for the solubility (mole fraction) of 2-amino-4-chloro-6-methoxypyrimidine in methanol/ethanol/acetone/DMF + water were 0.0002046–0.009616, 0.0002046–0.01060, 0.0002046–0.04918 and 0.0002046–0.1197, respectively. The Jouyban-Acree (JA), Apelblat-Jouyban-Acree (AJA) and van’t Hoff-Jouyban-Acree (VJA) model were applied to calculate the solubility data of 2-amino-4-chloro-6-methoxypyrimidine in mixtures. The preferential solvation parameter δx1,3 > 0 in 0.32 < xmethanol < 1, 0.24 < xethanol < 1, 0.21 < xacetone < 1 and 0.19 < xDMF < 1, the 2-amino-4-chloro-6-methoxypyrimidine was preferentially dissolved by cosolvents and the 2-amino-4-chloro-6-methoxypyrimidine was dissolved preferentially by water within δx1,3 < 0. What’s more, the interaction between solute - solvent molecules and the internal interaction of molecules was analyzed by extend Hildebrand solubility approach (EHSA) and in the concentration range with W > δ1+2δ3, the hydrophobic groups in the 2-amino-4-chloro-6-methoxypyrimidine played a dominant role, while in other ranges self associations of solute, solvent or both were observed. The dissolution thermodynamic properties were obtained by van’t Hoff plots and the ranges of values for ΔsolHo (kJ∙mol−1)/ ΔsolGo (kJ∙mol−1)/ ΔsolSo (J∙mol−1) were 9.74 – 31.12, −17.84 – 4.96 and 33.79 – 161.89.

Solubility of buprenorphine hydrochloride in supercritical carbon dioxide: Study on experimental measuring and thermodynamic modeling

Nowadays, supercritical fluids (SCFs) technologies present a processing option for obtaining new products with noteworthy characteristics. Access to reliable solubility data of pharmaceutical compounds in SCFs is considered as the first step for recrystallizing, separating, and producing nano particles via processes based on this type of technique. In this study, high-pressure solubility of buprenorphine hydrochloride, a strong pain reliever, in supercritical carbon dioxide (scCO2) was measured at temperature and pressure conditions of 308–338 K and 120–270 bar, for the first time. The minimum and maximum solubility values, in terms of equilibrium mole fractions, were found to be 0.131 × 10-4 (at 338 K and 120 bar) and 4.752 × 10-4 (at 338 K and 270 bar), respectively. Thereafter, the obtained data were correlated using two different approaches, namely Peng-Robinson (PR) equation of state (EoS) and a set of semi-empirical models. Results from applying statistical criteria indicated that Jouyban and Sodeifian models are suitable choices for predicting solubility data. Furthermore, using the obtained correlation results, the total and vaporization enthalpies of buprenorphine hydrochloride dissolution in scCO2 were estimated to be 65.59 and 85.60 kJ/mole, respectively.

Solubility of Salicylic Acid in Some (Ethanol + Water) Mixtures at Different Temperatures: Determination, Correlation, Thermodynamics and Preferential Solvation

Equilibrium mole fraction solubility of salicylic acid in nine aqueous-ethanolic mixtures, as well as in neat water and neat ethanol, was determined at seven temperatures from T = (293.15 to 323.15) K. Salicylic acid solubility in these mixtures was adequately correlated with well-known correlation/prediction methods based on Jouyban-Acree model. Apparent thermodynamic quantities, i.e. Gibbs energy, enthalpy, and entropy, for the dissolution and mixing processes, were computed by means of the van’t Hoff and Gibbs equations. The enthalpy–entropy compensation plot of enthalpy vs. Gibbs energy of dissolution was not linear exhibiting positive slopes from neat water to the mixture of w1 = 0.30 and from the mixture of w1 = 0.50 to neat ethanol indicating enthalpy-driven drug transfer processes but negative in the interval of 0.30 < w1 < 0.50 indicating entropy-driven drug transfer processes from more polar to less polar solvent systems. Moreover, by using the inverse Kirkwood–Buff integrals it is observed that salicylic acid is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by ethanol molecules in those mixtures of 0.24 < x1 < 1.00.

Study of Hyoscine solubility in scCO2: Experimental measurement and thermodynamic modeling

In this research, solubility of Hyoscine, as the most well-known drugs used to relieve spasmodic abdominal pain, in supercritical carbon dioxide (scCO2) was determined at 170–410 bar for pressure and 308–348 K for temperature. It was found 0.79 × 10-4 to 2.83 × 10-4 of equilibrium mole fraction and 0.3 × 10-2 to 1.65 × 10-2 kg.m−3 of equilibrium solubility. Also, obtained experimental data was correlated by common empirical models; Bartle, Chrastil, Mendez-Santiago, Kumar, and Johnston (K-J), and Teja (MST). All these models could satisfactorily correlate the experimental data with high accuracy. Among them, the MST model with the lowest AARD% value (2.942) and the highest Radj value (0.991) possesses the highest correlation precision. Furthermore, the total heat of mixing, enthalpy of vaporization, and enthalpy of solvation for the Hyoscine-scCO2 system were computed, as 20.76 kJ.mol−1, 35.71 kJ.mol−1, and −14.95 kJ.mol−1, respectively.

Diffusion coefficients and phase equilibria of carbon dioxide–ionic liquid, 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim][PF6]) system

AbstractThis article presents the mutual diffusion coefficients of a carbon dioxide–ionic liquid, [bmim][PF6], system at temperatures of 313.15 and 323.15 K and pressures of 5 and 8 MPa. In order to estimate the diffusion coefficients, we have carried out experiments to find time‐dependent carbon dioxide solubilities in the ionic liquid and then fit a transport model to the data. In a system containing high pressure carbon dioxide and ionic liquid, carbon dioxide dissolves in the liquid until its equilibrium mole fraction is reached. During this process, the position of the liquid–vapour interface and the density of the liquid phase change. To account for the variation in liquid density, an equation fit to the experimental density data is included in the transport model. To track the moving interface, the volume‐of‐fluid method is used. The diffusivities at dilute concentration and at thermodynamic phase equilibrium are determined and compared with the literature values and those obtained from correlations.

Equilibrium solubility and modeling of Glibenclamide in cosolvent mixtures of Methanol, n-Propanol, Isopropanol, and Acetonitrile + Water

Equilibrium solubility of glibenclamide (GCM) in aqueous solutions of methanol, n-propanol, isopropanol, and acetonitrile were studied by static technique at temperatures ranging from 288.15 K to 323.15 K under p = 101.3 kPa. When the composition of cosolvent was constant in the four mixed solvents, GCM solubility increased with the rising temperature. When the temperature was fixed, the GCM mole fraction solubility showed positive dependence on the increasing mass fraction of methanol in methanol + water mixture. While in solutions of n-propanol + water, isopropanol + water, and acetonitrile + water, it first increased as the mass fraction of cosolvent (w) added, at around w = 0.9, the solubility reached a maximum value and then it descended. Thermodynamic models like Jouyban−Acree model, modified Apelblat−Jouyban−Acree model, and CNIBS/R-K model were taken to correlate the equilibrium mole fraction solubility of GCM in four solvent mixtures. The maximum RAD and the RMSD values calculated by the CNIBS/R-K model were found in the mixture of methanol + water and didn’t exceeded 7.4 × 10−2 and 1.48 × 10−5, respectively. However, the maximum RAD values obtained by the Jouyban−Acree and modified Apelblat−Jouyban−Acree model were found in the mixture of acetonitrile + water and didn’t exceeded 5.57 × 10−2 and 5.55 × 10−2, respectively. The RMSD all didn’t exceeded 2.54 × 10−5. Hence, the Jouyban−Acree model and modified Apelblat−Jouyban−Acree model are shown to be superior to the CNIBS/R-K model in this work. The experimental data and model parameters obtained will be helpful for the preparation and purification of GCM.

Laboratory determination and thermodynamic analysis of alendronate solubility in supercritical carbon dioxide

Alendronic acid, with the commercial name of Alendronate, is a bisphosphonate medicine which is generally used orally to treat the osteoporosis and Paget's disease of bones. However, its absorption is poor, and its oral bioavailability is <1%. So, development of novel delivery systems to enhance its bioavailability and reduce its side effects is essential.The design a modern drug delivery systems, through supercritical carbon dioxide (scCO2) as a green solvent, which is known as an efficient solution to increase the drug bioavailability, reduce toxicity and side effects. Solubility of pharmaceutical substances in scCO2 is an essential parameter that must be determined for this purpose.Here, solubility of Alendronate was experimentally studied in the span of 0.01 × 10−4 to 1.5 × 10−4 (equilibrium mole fraction), at 308–338 K and 120–300 bar. Also, obtained experimental values were correlated by two fugacity coefficient models (PR-EoS and SRK-EoS), and two activity coefficient models (modified Wilson and UNIQUAC). All these models could successfully correlate the Alderonate solubility values. Meanwhile, the solubility data obtained from the SRK-EoS (AARD% = 10.11) and modified Wilson’s model (AARD% = 11.52) are more accurately fitted to the experimental data.

Solubility, dissolution thermodynamics, Hansen solubility parameter and molecular simulation of 4-chlorobenzophenone with different solvents

Equilibrium mole fraction solubility of 4-chlorobenzophenone in eleven organic solvents, as well as in neat water, was determined at temperatures ranging from 278.15 K to 323.15 K. Solubility of 4-chlorobenzophenone in these solvents increased with rising of temperatures, and the data was adequately correlated with several well-known thermodynamic models with the average relative deviations (100ARD) of 0.03 to 12.91%, suggesting good correlation. The effects of solvent polarity on solubility were also investigated, and 4-chlorobenzophenone dissolved more in less polar solvents (ester solvents) than in strong polar solvents (alcohol solvents) due to the weak polarity functional groups of 4-chlorobenzophenone. Respective apparent thermodynamic functions, i.e. Gibbs energy, enthalpy, and entropy, for the dissolution process, were calculated using the Wilson equation. Results showed that the dissolution process of 4-chlorobenzophenone was endothermic and spontaneous. Furthermore, Hansen solubility parameters (HSPs) were applied to further discuss the miscibility of 4-chlorobenzophenone in the selected solvents. Molecular dynamics simulation explored the molecular interaction between 4-chlorobenzophenone and solvents, and strong interaction between 4-chlorobenzophenone and ester solvents contributed to the higher solubility.

Investigation of the stability, radiation, and structure of laminar coflow diffusion flames of CH4/NH3 mixtures

The stability, radiation, and structure of laminar axisymmetric CH4/NH3/air diffusion flames have been studied using photographic images, spectrally resolved measurements of flame radiation, and the spatial distribution of temperature and major species mole fractions obtained by spontaneous Raman scattering. The fit procedure for the Raman spectra of NH3 includes a hitherto unquantified overtone feature, whose inclusion in the fit significantly improves the NH3 fraction obtained. Nitrogen is used to replace NH3 to separate chemical effects of NH3 addition from those due to dilution. The results show that NH3 addition drastically reduces radiation from carbon-containing species, with progressively increasing strong chemiluminescence from excited NO2 and NH2, indicating a substantial change in flame chemistry. While the Rayleigh/Mie scattering from soot particles is still observed in the Raman spectra at 28% NH3 addition, 46% NH3 in the fuel is seen to suppresses soot formation effectively. The measured axial and radial profiles of temperature and major species indicate a substantial contribution from radial transport from the reaction zone, seriously complicating the relation between composition, mixture fraction, and the corresponding equilibrium temperature and mole fractions.

Ab initio simulation of rarefied flows of gaseous mixtures in the system of microbeams with different temperatures

The issues of gas flows induced by inhomogeneous temperatures in a rarefied gas and exerting Knudsen force on the immersed structures are classic in the field of rarefied gas dynamics. The rarefied flows of HeNe gaseous mixtures in the system of microbeams with different temperatures for different combinations of equilibrium temperatures, rarefaction parameters, and mole fractions are studied using direct simulation Monte Carlo (DSMC) method in combination with ab initio (AI) potential with quantum scattering. Moreover, an extra simulation for VSS model is conducted by the same method to investigate the influence of inter-atomic potentials. The research results demonstrate that the rarefaction parameter for the maximum value of Knudsen force on the beams is related to the beam temperature. By comparing the results of AI and VSS potentials, it is found that the difference between the results predicted by the two potentials in the free-molecular regime is almost negligible. However, in transition regime or in an extremely low (or extremely high) temperature environment, the difference between the results is significant. In particular, in the transition regime with equilibrium temperature of 10 K, the maximum relative deviations of heat transfer coefficient and Knudsen force are 19.43% and 194.29%, respectively.

Investigation on the chemical equilibrium products for CnHmOlNk type fuels using equilibrium constants database

As international concern that regards NOx emissions from the shipping industry increases, it is challenging and urgent to reduce ships’ NOx emissions. According to the extended Zeldovich, the determination of the equilibrium concentration of combustion products is crucial for the prediction of NO formation in internal combustion engines. In the present work, an equilibrium constants database of related chemical reactions is established based on the theory that the total Gibbs energy reaches its minimum when a reaction achieves equilibrium. Afterward, a combustion product equilibrium model with twelve species considered is established based on the equilibrium constants database. The accuracy of the model is significantly improved compared with the commonly used ones which calculate the equilibrium constants through fitting function. The errors of the model are within 2% compared with STANJAN which is widely used for chemical equilibrium analysis. The model results are comparable to STANJAN. Afterward, the effects of the temperature, pressure, fuel–air equivalence ratio, O2 concentration, N2 concentration, Ar concentration and fuel type on the equilibrium mole fractions of the combustion products are investigated. The equilibrium concentration of combustion products is significantly affected by the temperature, O2 concentration and fuel–air equivalence ratio, but slightly influenced by the pressure and Ar concentration. The existence of O and N in the fuel slightly reduces the NO equilibrium mole fraction of the combustion products at the same temperature, pressure and fuel–air equivalence ratio. However, the ratio of molar carbon hydrogen in the fuel and the existence of O and N in the fuel have a significant impact on the CO2 mole fraction of the combustion products.

Solubility of 6-phenyl-4,5-dihydropyridazin-3(2H)-one in aqueous mixtures of Transcutol and PEG 400 revisited: Correlation and preferential solvation

Reported equilibrium mole fraction solubility values of 6-phenyl-4,5-dihydropyridazin-3(2H)-one (PDP-6) (3) in {Transcutol (1) + water (2)} and {PEG 400 (1) + water (2)} mixtures at five temperatures from T = (293.15 to 313.15) K were analyzed based on the Hildebrand solubility parameter of the respective aqueous mixtures. Cosolvency models for representing the equilibrium solubility of PDP-6 in both binary solvent systems at various temperatures were also provided for correlation/prediction purposes. Moreover, the preferential solvation parameters of PDP-6 in these aqueous-cosolvent mixtures at T = (298.15 and 313.15) K were determined by means of the “inverse Kirkwood-Buff integrals” (IKBI). PDP-6 is preferentially solvated by water in water-rich mixtures of {Transcutol (1) + water (2)} system but preferentially solvated by Transcutol in mixtures of 0.13 < x1 < 1.00. In the former case this result could be due to hydrophobic hydration around the non-polar moieties of PDP-6. Otherwise, PDP-6 is preferentially solvated by PEG 400 in all the aqueous mixtures. Moreover, in the systems where preferentially solvation of PDP-6 by cosolvents are observed, these results could be due to the Lewis acidic behavior of PDP-6 in front of Transcutol or PEG 400 molecules because these cosolvents exhibit higher Lewis basic behavior than water.

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.

Effect of temperature and polarity on the solubility and preferential solvation of sinapic acid in aqueous mixtures of DMSO and Carbitol

Reported equilibrium mole fraction solubilities of sinapic acid (3) in {DMSO (1) + water (2)} and {Carbitol (1) + water (2)} mixtures at several temperatures were analyzed in terms of the Hildebrand solubility parameter of these aqueous mixtures. Moreover, the preferential solvation parameters of sinapic acid in these aqueous saturated mixtures at (298.15 and 313.15) K were determined based on the inverse Kirkwood-Buff integrals (IKBI) as widely described in the literature. Sinapic acid is preferentially solvated by water in water-rich mixtures, i.e. (0.00 < x1 < 0.21 in {DMSO (1) + water (2)}) and (0.00 < x1 < 0.12 in {Carbitol (1) + water (2)}) but preferentially solvated by the cosolvents in the other mixtures composition. In the former cases these results could be interpreted as a consequence of hydrophobic hydration around the non-polar moieties of sinapic acid. Moreover, in the last cases, the observed trends could be due to the Lewis acidic behavior of sinapic acid in front of DMSO or Carbitol molecules because both cosolvents exhibit higher Lewis basic character than water, as indicated by the respective solvatochromic parameters. A single cosolvency model for representing the equilibrium solubility of sinapic acid in binary solvents at various temperatures was also provided based on a combination of Hansen solubility parameters and Jouyban-Acree model.

Carbon Clusters: Thermochemistry and Electronic Structure at High Temperatures.

This paper studies the thermochemistry and electronic structure of small carbon clusters and hydrocarbons, which are major constituents of pyrolysis gases released into the boundary layer of ablating heat shields. Our focus lies on clusters of up to four carbon atoms. Among other molecules, thermochemistry data for molecules such as C3H and C4H have been determined using the Weizmann-1 (W1) method. These molecules have very limited thermochemistry data recorded in the literature, thereby necessitating new and accurate computations of required properties such as electronic energies of low-lying states, heats of formation, harmonic frequencies, and rotational constants. A study of electronically excited states of these molecules computed using the equations of motion coupled cluster singles doubles method revealed C4 and C4H to be potential sources of radiation absorption in the boundary layer. The excited electronic states of interest are studied further to obtain their optimum geometries, rotational constants, and vibrational frequencies. Moreover, we also study the effect of low-lying excited electronic states on the partition function to assess their effect on the thermodynamics of these pyrolysis gases in the high-temperature regime. Neglecting the excited electronic states records a maximum difference of 12% in the computed specific heat capacity values, Cp values. Finally, comparisons of the equilibrium mole fractions obtained using the thermodynamics computed in this paper with the existing state-of-the-art tables used for hypersonic applications (e.g., JANAF and Gurvich Tables) show an order of magnitude difference in the mixture compositions. It is shown that the rhombic isomer of C4 (1Ag), which is energetically close to the ground state (3Σg-) and usually neglected in composition calculations, contributes to a 28% increase in the equilibrium mole fraction of the C4 molecule.

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.