Isobaric Molar Heat Capacities Research Articles

Characterization of camphor: thymol or dl-menthol eutectic mixtures; Structure, thermophysical properties, and lidocaine solubility

The low solubility of drugs in aqueous media is a major problem for the pharmaceutical industry. Among the solutions proposed, the use of eutectic mixtures can be highlighted. In them, the components used can also increase the therapeutic advantages of the active principle. In this work, we analyzed the solubility of lidocaine in mixtures of camphor + thymol or dl-menthol. These binary eutectic solvents were also characterized. For all this, several NMR techniques were used and different thermophysical properties (density, speed of sound, refraction index, isobaric molar heat capacity, surface tension, and kinematic viscosity) were measured. The results indicated that the interaction of camphor with thymol was stronger than with dl-menthol, providing a more compact fluid. On the contrary, the steric hindrance was greater in the mixture with dl-menthol, giving rise to a more viscous liquid. Furthermore, the lidocaine was significantly more soluble (up to 540 times) in these mixtures than in water. The lidocaine showed the strongest interactions with thymol molecules, somewhat weaker with dl-menthol, and the weakest were with camphor ones.

Bound-state energy spectrum and thermochemical functions of the deformed Schiöberg oscillator

In this study, a diatomic molecule interacting potential such as the deformed Schiöberg oscillator (DSO) have been applied to diatomic systems. By solving the Schrödinger equation with the DSO, analytical equations for energy eigenvalues, molar entropy, molar enthalpy, molar Gibbs free energy and constant pressure molar heat capacity are obtained. The obtained equations were used to analyze the physical properties of diatomic molecules. With the aid of the DSO, the percentage average absolute deviation (PAAD) of computed data from the experimental data of the 7Li2 (2 3Πg), NaBr (X 1Σ+), KBr (X 1Σ+) and KRb (B 1Π) molecules are 1.3319%, 0.2108%, 0.2359% and 0.8841%, respectively. The PAAD values obtained by employing the equations of molar entropy, scaled molar enthalpy, scaled molar Gibbs free energy and isobaric molar heat capacity are 1.2919%, 1.5639%, 1.5957% and 2.4041%, respectively, from the experimental data of the KBr (X 1Σ+) molecule. The results for the potential energies, bound-state energy spectra, and thermodynamic functions are in good agreement with the literature on diatomic molecules.

The investigation of crystal structure, thermodynamic properties, and fluorescence properties of three new rare earth coordination compounds

Three new rare earth coordination compounds [REL3Ph]2(RE = Pr(1), Sm(2)); [ErL3Ph]2·4C2H5OH(3); (L = 2,6-dimethylbenzoate, Ph = o-phenanthroline) were synthesized. The crystal structures of the three compounds were measured by X-ray single-crystal diffraction. From the results, we made out that compounds 1–3 were binuclear structures, and 1D chain-like structures could be formed by hydrogen bonding. The thermal degradation data of the compounds and the three-dimentional infrared cumulative spectra of the gaseous decomposed products were obtained by TG/DSC-FTIR technique, and the thermal degradation patterns were explained. The isobaric molar heat capacity of compounds 1 and 2 in the low-temperature region was obtained by the DSC technique and the thermodynamic parameters were derived. The fluorescence spectrum of compound 2 was determined, showing that it had potential application value in the orange-red luminescence region.

Deep Eutectic Solvents Formed by Glycerol and Xylitol, Fructose and Sorbitol: Effect of the Different Sugars in Their Physicochemical Properties.

The search for new eutectic solvents for different applications (extraction, drug formulation, chemical reactions, etc.) is booming thanks to their high solubility capacity and low toxicity. However, it is necessary to carry out a comprehensive physicochemical characterization of these mixtures to understand the molecular behavior at different experimental conditions. In this study, three deep eutectic solvents (DESs) formed by glycerol and xylitol, fructose and sorbitol and water in the molar ratio 1:2:3 were prepared and several physicochemical properties (refractive index, density, surface tension, viscosity, speed of sound, isobaric heat capacity and isentropic compressibility) were measured and analyzed in the 278.15-338.15 K temperature range. The results indicate a linear dependence with temperature for the following properties: surface tension, refractive index, density and isobaric molar heat capacity while viscosity values have been fitted to the Vogel-Fulcher-Tammann equation.

Thermodynamic and Thermal Analyze of N,N-Dimethylformamide + 1-Butanol Mixture Properties Based on Density, Sound Velocity and Heat Capacity Data.

The present paper contains data on the density (ρ), sound velocity (u), and specific heat capacity cp of the mixture of N,N-dimethylformamide + 1-butanol (DMF + BuOH) determined in the entire concentration range of solution and in the temperature range (293.15-318.15) K. The analysis of thermodynamic functions such as isobaric molar expansion, isentropic and isothermal molar compression, isobaric and isochoric molar heat capacity, as well as their excess functions (Ep,mE,KS,mE,KT,mE,Cp, mE,CV, mE) and also VmE was undertaken. The analysis of changes in the physicochemical quantities was based on consideration of the system in terms of intermolecular interactions and resulting changes in the mixture structure. The results available in the literature were confusing during the analysis and became the reason for our decision to thoroughly examine the system. What is more, for a system whose components are widely used, there is very scarce information in the literature regarding the heat capacity of the tested mixture, which was also achieved and presented in this publication. The conclusions drawn from so many data points allow us to approximate and understand the changes that occur in the structure of the system due to the repeatability and consistency of the obtained results.

On the interpretation of the unusual behavior of aqueous-organic mixtures in concentration regions with intersecting isotherms of heat capacity properties

Based on our own and some literature results, we have carried out a detailed analysis of concentration regions of the aqueous-organic mixture in which the temperature dependences of both excess molar heat capacity, CpE, and apparent molar heat capacity of each component, Cp,ϕ,i, are intersected. It is established that the ∂CpE/∂T and ∂Cp,ϕ,w/∂Tderivatives (W is water) for the {(W + hexamethylphosphoramide (HMPA)} and {(W + tert‑butanol (t-BuOH)} mixtures intersect in a rather narrow concentration interval between (0.30 and 0.35) and (0.35 and 0.40) mole fractions of the organic component, respectively. This fact we have interpreted as evidence that the decisive role in the mutually overlapping heat-capacity contributions to CpEresulting in such a situation plays the abnormal change in the isobaric molar heat capacity of W (Cp,w), which has a minimum at T ≈ 308 K, when the temperature increases.

Isobaric molar heat capacity model for the improved Tietz potential

AbstractIn this study, the improved Tietz potential was used to describe the internal vibration of diatomic molecules. By employing the expression for upper bound vibrational quantum number and canonical partition function of the system, equation for the prediction of constant pressure (isobaric) molar heat capacity of diatomic molecules was derived. The analytical model was used to predict the isobaric molar heat capacity of the ground state CO, BBr, HBr, HI, P2, KBr, Br2, PBr, SiO, and Cl2 molecules. The upper bound vibrational quantum number obtained for the molecules are 85, 100, 21, 21, 115, 301, 89, 157, 110, and 67. The calculated average absolute deviations are 2.3462%, 1.1342%, 2.3350%, 1.9078%, 0.7268%, 2.4041%, 1.7849%, 1.8989%, 2.5209%, and 2.1523% from experimental data. The results obtained are in good agreement with available literature data on gaseous molecules.

Study on the volatility of four benzaldehydes

This work reports the experimental determination of relevant thermodynamic properties of four benzaldehydes. The vapor pressures of both crystalline and liquid phases (including supercooled liquid) of syringaldehyde, 3,4,5-trimethoxybenzaldehyde, 4-(dimethylamino)benzaldehyde and of the liquid phase of veratraldehyde were determined using a static method based on capacitance diaphragm manometers. Additionally, the sublimation vapor pressures of the four compounds were also determined at different temperatures, using the Knudsen mass-loss effusion method. The experimental results allowed accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization for the benzaldehydes studied, at reference temperatures, allowing phase diagram representations of the (p,T) results, in the neighborhood of the triple point of the four compounds. Their temperatures and molar enthalpies of fusion were determined using differential scanning calorimetry and were compared with the ones obtained indirectly through vapor pressure measurements. Using high-precision drop calorimetry, the standard isobaric molar heat capacities of the four crystalline benzaldehydes were determined at 298.15 K. The enthalpy of the intermolecular hydrogen bond OH…O in the crystalline phase of syringaldehyde was estimated.

Measurement and correlation of isobaric molar heat capacities of deep eutectic solvents consisting of choline chloride and triethylene glycol

Deep eutectic solvents are environmentally friendly substitutes to room temperature ionic liquids in broad engineering applications like biofuel purification, polymer synthesis, gas capture, and organic extraction. In this work, the isobaric molar heat capacities of deep eutectic solvents consisting of choline chloride and triethylene glycol (in molar ratio of 1: 3, 1: 4, and 1: 5) are investigated by flow method in the temperature from 334.91 K to 364.98 K and pressure from 0.19 MPa to 25.21 MPa. The relative expended uncertainty of measurement system is calculated to be 1.4 % within 95 % degree of confidence. Experimental results show that the isobaric molar heat capacity increases linearly with higher temperature and lower pressure. With choline chloride added in triethylene glycol, the heat capacity decreases linearly with the decreasing of triethylene glycol molar fraction. Finally, the correlation of these binary mixtures is established based on the experimental data with the maximum absolute relative deviation and average absolute relative deviation of 1.01 % and 0.31 %, respectively.

Heat capacity of six glymes in N,N-dimethylformamide + water mixtures. Solvation of glymes

The paper presents the heat capacities of glyme solutions: monoglyme, diglyme, triglyme, tetraglyme, pentaglyme and hexaglyme, in binary solvents N,N-dimethylformamide + water at four temperatures (293.15 K, 298.15 K, 303.15 K, 308.15 K) obtained using differential calorimeter Micro DSC III, Setaram – France. The concentration of glymes was approximately 0.25 mol/kg. On the basis of the obtained experimental results, the apparent isobaric heat capacities of the glymes were calculated. It was noted that the larger the glyme molecule was, the more pronounced the increase in the value of the apparent molar heat capacity function with the increase in water content in the two-component solvent. The observed changes in apparent isobaric heat capacity as a function of the water content in the mixed solvent are discussed in terms of the hydrophobic nature of the glymes. Moreover, it was shown that the apparent molar isobaric heat capacity of the glymes in pure solvents, i.e. in water and in N,N-dimethylformamide, increases linearly with the increase in the number of oxygen atoms in the glyme molecules i.e. with the size of glyme molecules. Furthermore, a linear correlation was observed between the apparent isobaric molar heat capacity and the enthalpic effect of the hydrophobic hydration of the studied glymes at 298.15 K. The results obtained in this paper are compare with the same obtained for selected cyclic ethers.

Isobaric molar heat capacities of dimethyl carbonate and alkane binary mixtures at high pressures

Isobaric molar heat capacities of dimethyl carbonate and alkane binary mixtures at high pressures

Thermophysical characterization of choline chloride: Resorcinol and its mixtures with water

The study of deep eutectic solvents has increased in recent years. This is because of their great solubility ability and lower toxicity than usual organic solvents. In this work, deep eutectic solvents formed by choline chloride and resorcinol in the mole ratio 1:2 and its mixtures with water, e.g., choline chloride:resorcinol:water 1:2:1.05 (water mass fraction = 0.05) and choline chloride:resorcinol:water 1:2:2.22 (water mass fraction = 0.1), have been studied. Several physicochemical properties (density, speed of sound, isentropic compressibility, refractive index, surface tension, isobaric molar heat capacity, viscosity, and electrical conductivity) have been obtained and analysed at atmospheric pressure in the range of 283.15–338.15 K. The starting temperature for the speed of sound measurements was 308.15 K. The effects of temperature and water inclusion have been evaluated. The obtained results have shown a linear correlation between density, speed of sound, refractive index, surface tension and isobaric molar heat capacity and temperature. Additionally, the viscosity and electrical conductivity data can be adjusted using the Vogel-Fulcher-Tammann equation. Finally, the inclusion of water was analysed to check how the thermophysical properties were modified. These modifications had greater effects on transport properties, viscosity and electrical conductivity.

Isobaric Molar Heat Capacities of Binary Mixtures of Diethyl Carbonate and Methyl Caprate at High Pressures

Isobaric Molar Heat Capacities of Binary Mixtures of Diethyl Carbonate and Methyl Caprate at High Pressures

Thermophysical Study of Pyridinium-Based Ionic Liquids Sharing Ions.

The thermophysical properties of three pyridinium-based ionic liquids sharing ions were measured at several temperatures (278.15-338.15) K and at atmospheric pressure (0.1 MPa). Three ionic liquids were studied: 1-butylpyridinium bis(trifluoromethyl-sulfonyl)imide, 1-hexylpyridinium bis(trifluoromethylsulfonyl)imide, and 1-hexylpyridinium tetrafluoroborate. The following thermophysical properties were measured: density, speed of sound, refractive index, surface tension, isobaric molar heat capacity, kinematic viscosity, and electrical conductivity. The thermophysical properties at atmospheric pressure were correlated with temperature, noting that the starting temperature for the speed of sound measurements depended on the ionic liquid. From these experimental results, some derived properties (isentropic compressibility, molar refraction, and dynamic viscosity) are calculated. These results together with those published previously for 1-butylpyridinium tetrafluoroborate are discussed.

Molar heat capacity of liquid Ti, Al20Ti80 and Al50Ti50 measured in electromagnetic levitation

Temperature dependent isobaric molar heat capacity cP was measured in a containerless way for liquid Ti and two AlTi binary liquid alloys. The technique of electromagnetic levitation was used in combination with laser modulation calorimetry. In all cases, linear temperature dependencies were found: At the corresponding liquidus temperatures, cP equals 49.75(±2.0) J∙K-1mol-1, 57.43(±2.9) J∙K-1mol-1, and 42.60(±2.2) J∙K-1mol-1, for Ti, Al20Ti80 and Al50Ti50, respectively. The respective temperature coefficients amount to -1.67∙10-2J∙K-2mol-1, -2.73∙10-2J∙K-2mol-1, and +7.83∙10-2J∙K-2mol-1. For liquid Ti, there is a good agreement with existing literature data. The results are discussed in relation to the Neumann-Kopp rule.

Thermodynamic Stability of Fenclorim and Clopyralid.

The present work reports an experimental thermodynamic study of two nitrogen heterocyclic organic compounds, fenclorim and clopyralid, that have been used as herbicides. The sublimation vapor pressures of fenclorim (4,6-dichloro-2-phenylpyrimidine) and of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were measured, at different temperatures, using a Knudsen mass-loss effusion technique. The vapor pressures of both crystalline and liquid (including supercooled liquid) phases of fenclorim were also determined using a static method based on capacitance diaphragm manometers. The experimental results enabled accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation for both compounds and of vaporization for fenclorim, allowing a phase diagram representation of the (p,T) results, in the neighborhood of the triple point of this compound. The temperatures and molar enthalpies of fusion of the two compounds studied were determined using differential scanning calorimetry. The standard isobaric molar heat capacities of the two crystalline compounds were determined at 298.15 K, using drop calorimetry. The gas phase thermodynamic properties of the two compounds were estimated through ab initio calculations, at the G3(MP2)//B3LYP level, and their thermodynamic stability was evaluated in the gaseous and crystalline phases, considering the calculated values of the standard Gibbs energies of formation, at 298.15 K. All these data, together with other physical and chemical properties, will be useful to predict the mobility and environmental distribution of these two compounds.

Effect of Cross-Linking Density on Horizontal and Vertical Shift Factors in Linear Viscoelastic Functions of Epoxy Resins

Epoxy resins are an important class of thermosetting resins, and their network structure, obtained by the curing reaction of epoxy and amine compounds, plays an important role in the material properties. We here revisited a time–temperature superposition (TTS) principle applied to the dynamic viscoelastic functions of epoxy resins, in which the network was well defined and systematically varied on the basis of the length of n-alkyl diamine. The superimposition of isothermal curves in the frequency domain required not only a horizontal shift but also a vertical shift, regardless of the length of n-alkyl diamine. The temperature dependence of the horizontal shift factor, aT, could be well expressed by the Williams–Landel–Ferry equation. The fitting parameter, called C2, increased with decreasing alkyl chain length of the diamine, meaning that the thermal expansion of the free volume was suppressed due to greater cross-linking density. This was qualitatively confirmed by a full-atomistic molecular dynamics (MD) simulation. Meanwhile, the vertical shift factor, bT, increased with increasing temperature, and the extent was smaller with increasing cross-linking density. This can be explained in terms of the entropic contribution to the modulus in the temperature region above the glass transition temperature. The entropy change estimated using the isobaric molar heat capacity from the MD simulation strongly supported this hypothesis. The knowledge here obtained should be useful for a better design of thermosetting polymers as well as for the prediction of long-term durability.

Volumetric properties of binary mixtures of tetrahydrofuran, dimethyl adipate, 1-butanol and 2-butanol from (288.15 to 323.15) K and modeling by Prigogine-Flory-Patterson (PFP) and Extended Real Association Solution (ERAS) models

In this work, experimental densities data of the binary system tetrahydrofuran + 2-butanol have been determined at eight temperatures, T=(288.15–323.15) K and atmospheric pressure and used for excess molar volume calculations. Also, partial molar volumes, excess partial molar volumes and partial molar volumes at infinite dilutions were calculated for further non-ideal behaviour of binary mixture. Excess molar volume, VE, of experimental determined system tetrahydrofuran + 2-butanol, and four previously published binary systems, tetrahydrofuran + 1-butanol, dimethyl adipate + 1-butanol, dimethyl adipate + 2-butanol and dimethyl adipate + tetrahydrofuran were correlated with two models, Prigogine-Flory-Patterson (PFP) and Extended Real Association Solution (ERAS). In order to apply the proposed models additional data of ultrasonic speed of sounds for pure components, dimethyl adipate, tetrahydrofuran, 1-butanol and 2-butanol, were measured in the temperature range T=(288.15–323.15) K and at atmospheric pressure. Volumetric coefficients, thermal expansion coefficient α and isothermal compressibility κ were calculated from density, ultrasonic speed of sound and isobaric heat capacity data. Isobaric molar heat capacities Cp,m at all temperatures for all pure components were obtained by correlation of literature data.Both models, PFP and ERAS were used for analysis of molecular interactions present in the investigated solutions.

JPCRD: 50 Years of Providing the Scientific Community with Critically Evaluated Thermodynamic Data, Predictive Methods, and Large Thermodynamic Data Compilations

A brief overview is provided on articles published in the Journal of Physical and Chemical Reference Data containing experimental thermodynamic data as well as group contribution methods used to predict thermodynamic quantities of organic compounds. Published papers have contained large compilations of experimental and calculated condensed-phase and gas-phase standard molar enthalpies of formation, isobaric molar heat capacities, molar enthalpies of fusion, molar enthalpies of sublimation, and molar enthalpies of vaporization.

Densities, heat capacities, viscosities, 1H- and 13C-NMR spectra, and solvatochromic parameters of binary mixtures of 1,3-dimethyl-1,3-diazinan-2-one (DMPU) and water

The compound 1,3-dimethyl-1,3-diazinan-2-one (N,N’-dimethylpropyleneurea, DMPU) is a dipolar aprotic solvent with very strong electron-donating abilities but which is much less toxic and less carcinogenic than similar solvents such as the widely used HMPA (hexamethylphosphorictriamide). This paper reports densities and viscosities of the binary mixtures of (DMPU + water) in the temperature range (293.15 to 353.15) K at 5 K intervals, over the whole composition range. Isobaric heat capacities of these mixtures were measured by flow calorimetry at 298.15 K. The 1H- and 13C-NMR spectra as well as the solvatochromic parameters (polarizability, π*, hydrogen-bond acceptor basicity, β, and hydrogen-bond donor acidity, α) of the mixtures were also determined. The densities and viscosities were sensitive to traces of water in the organic-rich region while the heat capacities were not. Excess molar volumes were strongly negative, showing an extremum at mole fraction xDMPU ≈ 0.40. The variation of viscosity with mixture composition was similar to the density with a sharp maximum at xDMPU ≈ 0.35. Apparent molar volumes, Vϕ, of the mixtures show that the water-DMPU interactions have a larger effect on Vϕ of water than on DMPU. While the standard isobaric molar heat capacity of DMPU in water is much higher than that of DMPU itself, the corresponding value for water in DMPU was not much influenced by the presence of DMPU. The 1H-NMR spectra show that the chemical shift of the water protons is more influenced by mixture composition than those of the DMPU protons. A de-shielding of the DMPU carbonyl carbon resonance was observed in the 13C-NMR spectra at low xDMPU, indicative of H-bonding between the water protons and the non-bonding electrons of the carbonyl oxygen.