Standard Enthalpies Of Solution Research Articles

Solubilities of d-xylose in water + (acetic acid or propionic acid) mixtures at atmospheric pressure and different temperatures

Using dynamic method and the laser monitoring observation technique, the solubility of d-xylose in water+acetic acid, and water+propionic acid was measured over the temperature range (296.65–325.45)K at atmospheric pressure. The solubility of d-xylose in the mixtures of water+acetic acid, and water+propionic acid was found to increase with increasing temperature and decrease with increasing volume fractions of acetic acid, and propionic acid in aqueous solution. The experimental data were correlated by using the Apelblat equation, the λh equation and the ideal equation. The results showed that these three models agreed well with the experimental data, and the Apelblat equation was found to regress the solubility data better than the other two models. The standard enthalpy, standard entropy, and Gibbs free energy change of solution of d-xylose were calculated from the solubility data by using the Apelblat model.

Interaction of Some Aminophosphonic Acids with Urea in Aqueous Solutions at 298.15 K

The enthalpies of solution of aminomethylphosphonic acid (GlyP), 1-aminoethylphosphonic acid (AlaP), and 1-aminopropylphosphonic acid (HalaP) have been measured in water and aqueous urea solutions at 298.15 K. From the obtained experimental results, the standard enthalpies of solution of aminophosphonic acids (AP) in water–urea solutions have been determined. These data were used to calculate the heterogeneous enthalpic pair interaction coefficients based on McMillan–Mayer's formalism. These values were interpreted in the terms of the hydrophobic effect of the side chains of aminophosphonic acids on their interactions with a molecule of urea in water.

Effect of temperature on the process of preferential solvation of 1,4-dioxane and 12-crown-4 ethers in the mixture of water with formamide

The dissolution enthalpy of 1,4-dioxane and 12-crown-4 ethers in the mixture of water (W) and formamide (F) was measured at four temperatures: 293.15K, 298.15K, 303.15K, 308.15K. The standard molar enthalpy of solution, ΔsolH°, depends on the size of cyclic ethers and on temperature. The values of ΔsolH° become more negative with increasing molecule size and they increase in magnitude with increasing temperature. The effect of temperature on the process of preferential solvation of cyclic ethers has been discussed.

Study of the interaction between ethanol and natural amino acids containing ionic side groups in water at T = 298.15 K

The enthalpies of solution of l-α-aspartic acid, l-α-glutamic acid, l-α-arginine, l-α-lysine, and l-α-histidine have been measured in aqueous ethanol solutions at 298.15 K. From the obtained experimental results, the standard enthalpies of solution of amino acids in water–ethanol solutions have been determined. These data were used to calculate the heterogeneous enthalpic pair interaction coefficients based on McMillan–Mayer’s formalism. These values were interpreted in the terms of the ionic or no polar effect of the side chains of l-α-amino acids on their interactions with a molecule of ethanol in water.

Effect of temperature on the solvation of 15-crown-5 ether in water–methanol mixtures

The enthalpies of solution of 15-crown-5 (15C5) ether in methanol–water mixtures have been measured at 293.15–308.15K. The values of standard enthalpies of solution of 15-crown-5 ether are negative in the region up to about 0.9mol fraction of water and then they become positive. The relative importance of the solvation mechanism appeared to depend on co-solvent properties. The effect of temperature on the solvation process of 15C5 in the mixture of water with methanol was discussed.

Study on the enthalpy of solution and enthalpy of dilution for the ionic liquid [C 3mim][Val] (1-propyl-3-methylimidazolium valine)

A new amino acid ionic liquid (AAIL) [C 3mim][Val] (1-propyl-3-methylimidazolium valine) was prepared by the neutralization method. Using the solution-reaction isoperibol calorimeter, molar solution enthalpies of the ionic liquid [C 3mim][Val] with known amounts of water and with different concentrations in molality were measured at T = 298.15 K. In terms of standard addition method (SAM) and Archer’s method, the standard molar enthalpy of solution for [C 3mim][Val] without water, Δ s H m ∘ = (−55.7 ± 0.4) kJ · mol −1, was obtained. The hydration enthalpy of the cation [C 3mim] +, Δ H + ([C 3mim] +) = −226 kJ · mol −1, was estimated in terms of Glasser’s theory. Using the RD496-III heat conduction microcalorimeter, the molar enthalpies of dilution, Δ D H m( m i → m f), of aqueous [C 3mim][Val] with various values of molality were measured. The values of Δ D H m( m i → m f) were fitted to Pitzer’s ion-interaction model and the values of apparent relative molar enthalpy, φL , calculated using Pitzer’s ion-interaction model.

Thermochemistry of ethyl acetate solvation in the 1-octanol-N,N-dimethylformamide system

The thermal effects of ethyl acetate (EtOAc), 1-octanol (OctOH), and N,N-dimethylformamide (DMF) solution in a OctOH-DMF model system were measured using a calorimeter of variable temperature with an isothermal shell at 298 K. The standard enthalpies of solution and ester transfer from an alcohol to a binary mixture, and partial mole enthalpies of mixed solvent components were determined. The state of non-electrolyte molecules in OctOH-DMF and OctOH-DMF-EtOAc systems were studied using extended coordination model. It was found that the binary solvent is subjected to microclusterization, since the fraction of the single-type molecules in the solvation sphere of both components of a mixture is significantly higher than in the liquid phase volume. The conclusion was drawn that in the triple system, the ethyl acetate solvation sphere in the whole range of compositions is significantly enriched with amide owing to stronger esteramide dipole-dipole interaction.

Water as a solute in aprotic dipolar solvents: 3. D 2O–H 2O solute isotope effects on the enthalpy of water dissolution in dimethylsulphoxide, N, N-dimethylformamide and N, N-dimethylacetamide at 298.15 K

The enthalpies of solution of ordinary (H 2O) and heavy (D 2O) water in dimethylsulphoxide (DMSO), N, N-dimethylformamide (DMF) and N, N-dimethylacetamide (DMA) have been measured using an isoperibol sealed calorimeter at 298.15 K. Standard (at infinite dilution) enthalpies of solution and solvation, together with D 2O–H 2O solute isotope effects on the quantities in question, were calculated. The enthalpies of solution of water H/D isotopologues have been found to be negative by sign and increasing in magnitude on going from DMF to DMSO and DMA. The corresponding positive solute isotope effects are very insignificant and slightly increase in a consequence: DMF < DMSO ≤ DMA. It has been concluded that the enthalpy-isotopic effects of water solvation are qualitatively connected with the donor-accepting and structure-packing properties of the aprotic dipolar solvents compared.

Influence of the composition of aqueous-alcohol solvents on the thermodynamic characteristics of l-phenylalanine dissolution at 298.15 K

The enthalpies of l-phenylalanine dissolution in aqueous methanol, ethanol, 1-propanol and 2-propanol have been determined by calorimetry at 298.15 K and alcohol mole fractions up to x 2 ∼0.4. The standard enthalpies of solution Δ sol H° and transfer Δ tr H° from water to the mixed solvent as well as the enthalpy coefficients of l-phenylalanine–alcohol pair-wise interactions were calculated. The interrelation of the enthalpies of dissolution and transfer for l-phenylalanine with structural features of alcohols has been determined. A comparative analysis of the thermodynamic characteristics of dissolution of l-phenylalanine and some other amino acids (glycine, l-alanine, l-threonine and l-valine) in the mixtures studied has been made.

Saturation molalities and standard molar enthalpies of solution of α-d-xylose(cr) in H2O(l); standard molar enthalpies of solution of 1,4-β-d-xylobiose(am), and 1,4-β-d-xylotriose(am) in H2O(l)

The saturation molality of α-d-xylose(cr) in water was measured by using HPLC and is m(sat)=(8.43±0.42)mol·kg−1 at T=298.15K. It was also established that the anhydrous form of α-d-xylose(cr) is the crystalline form that is in equilibrium with the aqueous solution at T=298.15K. Solution calorimetry was used to measure the following standard molar enthalpies of solution at T=298.15K: ΔsolHm∘=(12.10±0.12)kJ·mol−1 for α-d-xylose(cr); ΔsolHm∘=−(8.1±2.7)kJ·mol−1 for 1,4-β-d-xylobiose(am); and ΔsolHm∘=−(24.1±6.4)kJ·mol−1 for 1,4-β-d-xylotriose(am). It was observed that both 1,4-β-d-xylobiose(am) and 1,4-β-d-xylotriose(am) were amorphous substances and that they form thick gels in water in which no solid phase is present. Consequently, it is not possible to measure m(sat) for these two substances. All substances were carefully characterized by using both HPLC and Karl Fischer analysis. NMR was used to measure the anomeric purity of the α-d-xylose(cr). Thermodynamic network calculations were used to calculate standard molar formation properties for the aforementioned substances.

Enthalpy-related interaction parameters in H/D isotopically distinguishable aqueous solutions of tetramethylurea cyclic derivatives at 298.15 K

The enthalpies for dilution of solutions of 1,1,3,3-tetramethylurea (TMU), 1,3-dimethylethyleneurea (DMEU), 1,3-dimethylpropyleneurea (DMPU) and 2,4,6,8-tetramethyl- bis-urea (TM bU) in ordinary (H 2O) and heavy (D 2O) water were measured calorimetrically at 298.15 K. The enthalpy coefficients for pair ( h 22) and triplet ( h 222) interactions between hydrated solute molecules were estimated using the McMillan–Mayer formalism. The quantities of h 22 as well as the corresponding solvent isotope effects were found to be positive for aqueous TMU, DMPU and DMEU and negative for aqueous TM bU. The correlation between h 22 and standard enthalpies of solution of these compounds in H 2O and D 2O was established at the temperature in question.

Dependence of the solution and transfer enthalpies of DL-α-alanyl-DL-α-asparagine on the composition of water-amide binary solvents at 298.15 K

Solution enthalpies of DL-α-alanyl-DL-α-asparagine (AlaAsn) in water-formamide, water-N-methylformamide, water-N,N-dimethylformamide, and water-N,N-dimethylacetamide mixtures were measured in the range of amide mole fractions x 2 = 0–0.3. The standard enthalpies of solution (Δsol H°) and transfer (Δtr H°) of AlaAsn from water to the binary solvent and enthalpy coefficients of pair-wise interactions (h xy ) of AlaAsn with amide molecules were calculated. The influence of the composition of the water-organic mixture on the enthalpy characteristics of AlaAsn is discussed. It is shown that the enthalpy characteristics of solution and transfer of AlaAsn are related to the structure of amides.

Solubility behaviour of griseofulvin in fatty acids

Abstract The solubility of griseofulvin in the straight-chain alkanoic acids from C2 to C22 and in the C4 and C5 alkanoic acids branched at C-2 was measured at various temperatures. The enthalpy of fusion of griseofulvin, measured by differential scanning calorimetry, was 39.39 kJ mol−1 at the melting point (495.15 K) and 36.95 kJ mol−1 at 373.15 K. The standard Gibbs free energy (ΔG°), standard enthalpy (ΔH°) and standard entropy (ΔS°) of solution were calculated at 373.15 K, from the van't Hoff plot of the temperature dependence of the mole fraction solubility in terms of the pure supercooled liquid solute as the standard state. With increasing chain length of the alkanoic acid solvents, ΔG° increased in parallel with the increase in pKa of the acids in water, suggesting that the solubility behaviour involves specific solute-solvent proton interactions, while ΔH° and ΔS° fluctuated but tended to decrease in parallel with the corresponding decreases in their enthalpies and entropies of ionization, respectively. The fluctuations in ΔH° and ΔS° may be attributed to the different solid adducts containing griseofulvin and the solvent. An observed non-linear (logarithmic) decrease in solubility with decreasing molality of the carboxyl group in the liquid solvent on ascending the homologous series is attributed to the disturbing influence of the hydrocarbon chains on the specific solute-solvent hydrogen bonding. Chain-branching of the solvent at C-2 gave a reduced solubility of griseofulvin and higher ΔG°, ΔH° and ΔS° values compared with the corresponding straight chain acid.

Enthalpies of solution of glycylglycylglycine in aqueous solution of amides at 298.15 K

Calorimetric measurements have been carried out at 298.15 K in aqueous solutions of glycylglycylglycine containing formamide, N-methylformamide, N, N-dimethylformamide and N, N-diethylformamide at concentrations of amides as co-solvents up to 0.4 mole fractions. The results obtained have been used to calculate the standard enthalpies of solution (Δ sol H°) and transfer (Δ tr H°) of the glycylglycylglycine from water into the mixtures as well as enthalpy coefficients of pair-wise interaction ( h xy ) of the solute with amide in aqueous media. The h xy values were correlated with the properties of organic solvents using Kamlet–Taft equation. The results of the calorimetric measurements have been discussed with regard to the intermolecular interactions occurring in these systems.

Partial Conductivities and Chemical Diffusivities of Mixed Protonic–Electronic Conducting CaZr0.9Y0.1O3 − δ

The electrical properties of (CZY) were studied as a function of both oxygen partial pressure and water vapor partial pressure in the temperature range of and the partial conductivities of protons, holes, and oxygen vacancies were calculated from the defect model. In a wet atmosphere, CZY was a mixed conductor of protons, holes, and oxygen ions. No conduction transition from protons to holes and/or oxygen ions occurred even as temperature was increased up to . The calculated activation energy of proton transport was . The standard solution enthalpy for water dissolution was best fitted with a slope of . The twofold conductivity relaxation behavior that was observed at during hydration/dehydration was interpreted in terms of decoupled ambipolar diffusion of oxygen vacancies and protons by holes. The best-estimated chemical diffusivities of oxygen and hydrogen were several orders of magnitude lower than that reported for other proton-conducting perovskite oxides due to the relatively low ion conductivity of CZY.

Enthalpy of Solvation of Monoglyme, Diglyme, Triglyme, Tetraglyme, and Pentaglyme in Mixtures of Water with N,N-Dimethylformamide at 298.15 K

The standard molar enthalpies of solution of linear polyethers (LPs) such as 1,2-dimethoxyethane (monoglyme), diethyleneglycol dimethyl ether (diglyme), triethyleneglycol dimethyl ether (triglyme), tetraethyleneglycol dimethyl ether (tetraglyme), and pentaethyleneglycol dimethyl ether (pentaglyme) in a mixture of water and N,N-dimethylformamide were measured at a temperature of 298.15 K. The values of standard molar enthalpy of solution, ΔsolHmo, the enthalpic effect of hydrophobic hydration, Hb(H2O), and the enthalpic effect of cyclization of these glymes have been determined. The values of standard molar enthalpy of solution of LPs are more negative than those of their cyclic equivalents. The exothermic enthalpic effect of hydrophobic hydration of LPs increases linearly with the increase in the number of −CH2− groups. The values of the standard molar enthalpy of solution and the enthalpic effect of hydrophobic hydration of LPs calculated in this paper have been compared to those data for cyclic polyethers (CPs) obtained earlier. The contributions of particular groups (−CH2−, −O−, and −CH3) to the enthalpic effect of hydrophobic hydration have been calculated.

Effect of Temperature on the Process of Hydrophobic Hydration. Part II. Hydrophobic Hydration of 15-Crown-5 and 18-Crown-6 Ethers

The dissolution enthalpy of 1,4,7,10,13-pentaoxacyclopentadecane (15-crown-5) and 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) ethers in the mixture of water and N,N-dimethylformamide (DMF) was measured within the range from (293.15 to 308.15) K. The values of standard molar enthalpies of solution, ΔsolHmo, of crown ethers: 15-crown-5 and 18-crown-6 in the mixture of water and N,N-dimethylformamide within the range of the mixture composition under investigation, increase linearly with increasing temperature. The values of partial molar heat capacity, Cp,2o, and hydrophobic hydration effect, Hb(H2O), were determined. The effect of temperature on the process of hydrophobic hydration of crown ethers has been interpreted. The values of the enthalpic effect of hydrophobic hydration are more negative for 18-crown-6 than those for 15-crown-5. The exothermic enthalpic effect of hydrophobic hydration, Hb(H2O), of the crown ethers under investigation decreases linearly with increasing temperature.

Water as a solute in aprotic dipolar solvents. 2. D 2O–H 2O solute isotope effects on the enthalpy of water dissolution in nitromethane, acetonitrile and propylene carbonate at 298.15 K

The enthalpies of solution of ordinary (H 2O) and heavy (D 2O) water in nitromethane (NM), acetonitrile (ACN) and propylene carbonate (PC) were measured calorimetrically at 298.15 K. Standard (at the infinite dilution) enthalpies of solution and solvation, along with D 2O–H 2O solute isotope effects on the quantities in question, were calculated. The enthalpies of solution of water H/D isotopologues were found to be positive by sign and substantially increasing in magnitude on going from ACN and PC to NM, whereas the corresponding positive solute H/D isotope effect changes in a consequence: NM > ACN > PC. The qualitative interrelations between the enthalpy–isotopic effect of dissolution (solvation) of water and the electron-accepting/donating ability of aprotic dipolar solvent (within a series considered) were found.

Thermal properties of n-R4NBr solutions in binary solvents containing formamide

The enthalpies of solution of tetraethyl- and tetra-n-hexylammonium bromides have been measured in mixtures of formamide with ethylene glycol at 298.15 and 313.15 K in the whole mole fraction range by the calorimetric method. The standard enthalpies of solution in binary mixtures have been calculated with Redlich–Rosenfeld–Meyer type equation. The enthalpy and heat capacity parameters of pair interaction of organic electrolytes with EG in FA and with FA in EG have been computed and discussed. The enthalpy interaction parameters of single ions with EG in FA medium have been evaluated and compared with those for ion–water and ion–MeOH interaction in FA. The standard heat capacities of solution have been evaluated. The excess enthalpies of solution, ΔsolHE, of Et4NBr, Bu4NBr, and Hex4NBr have been determined. The ΔsolHE values are positive for Et4NBr and negative for Bu4NBr and Hex4NBr and become more negative from Bu4NBr to Hex4NBr.

Thermal properties of tetraalkylammonium bromides in several solvents

Abstract Enthalpies of solution of tetra-n-hexylammonium bromide in anhydrous methanol (MeOH), formamide (FA), and ethylene glycol (EG) have been measured at 298.15 and 313.15 K. The integral solution enthalpies (ΔsolHm) of Hex4NBr and literature data for Et4NBr and Bu4NBr have been extrapolated to infinite dilution using the Redlich–Rosenfeld–Meyer-type equation to give the corresponding standard enthalpies of solution (ΔsolH0). Linear correlation between ΔsolH0(Bu4NBr) and ΔsolH0 (Hex4NBr) has been obtained in MeOH, FA, and EG. Relations allowing to predict the ΔsolH0 value of Hex4NBr in FA, NMF, DMF, and NMA at various temperatures have been proposed. The integral heat method has been employed to obtain partial molar heat capacities of the tetraalkylammonium bromides in MeOH, FA, and EG. It has been shown that the values of Et4NBr and Bu4NBr in methanol and formamide determined by this method are in good agreement with values obtained by the flow calorimetry data.