Condensed Phase Heat-capacity Research Articles

Heat capacities of active pharmaceutical ingredients nifedipine, griseofulvin, probucol and 5,5-diphenylhydantoin

AbstractThe isobaric condensed-phase heat capacities of selected pharmaceutical active ingredients (APIs), namely nifedipine (CAS RN: 21829-25-4), griseofulvin (CAS RN: 126-07-8), probucol (CAS RN: 23288-49-5) and 5,5-diphenylhydantoin (CAS RN: 57-41-0), were determined over a wide temperature range starting from 2 K by combination of relaxation (heat pulse) calorimetry, Tian-Calvet calorimetry and power-compensated differential scanning calorimetry. Heat capacity measurements were taken for clearly specified polymorphs, a liquid phase (including subcooled liquid) and a glassy amorphous phase, if feasible. For 5,5-diphenylhydantoin, a heat capacity anomaly was detected in the temperature range 160 to 190 K and interpreted based on additional calorimetric and temperature-variable crystallographic measurements as a sequence of two phase transitions, which are reported for the first time in this work. Based on the determined phase behavior and heat capacity data from near 0 K, standard thermodynamic functions for crystalline and liquid phases were calculated for all APIs studied. This work significantly extends the availability of reliable heat capacity data and related thermodynamic properties for APIs required for modeling their solubility and other applications involving thermodynamic modeling.

New static apparatus STAT9 for vapor pressure measurements at temperatures up to 463 K

In this work, a state-of-the-art static apparatus for vapor pressure measurements in a temperature range of 363−463 K and a wide pressure range of 1−13,330 Pa is introduced and described. The performance of the apparatus was evaluated by a meticulous procedure of measuring the vapor pressure of five reference materials of different volatility, anthracene, benzophenone, ferrocene, naphthalene, and dibenzothiophene. The last two compounds were studied in the blind test regime, i.e., the results were compared to literature only after finishing the experiments. During benchmarking the performance of the apparatus, it was found appropriate to develop new vapor pressure equations for ferrocene and anthracene that included high-temperature data from the STAT9 apparatus. By combining the new data with previously selected vapor pressures, sublimation enthalpies, and ideal-gas and condensed phase heat capacities, we have obtained a consistent sublimation pressure equation for anthracene and ferrocene. For anthracene, the correlation procedure covered melting properties and liquid-phase vapor pressure data to support the description of the high-temperature region. The revised vapor pressure equations and sublimation enthalpies may serve as solid foundation for future research in this field.

Thermodynamic study of selected aromatic monoterpenoids

Thermodynamic properties of aromatic alcohols thymol, carvacrol, and cuminol were studied in this work as part of our effort to establish reliable physicochemical data for common monoterpenes. The phase behavior of the compounds was investigated by heat-flux differential scanning calorimetry (DSC) above 183 K with a special focus on the signs of polymorphic behavior. The heat capacities of the condensed phases were determined by a Tian-Calvet type calorimeter. Vapour pressure measurements were performed using two static apparatus over a wide temperature range, including environmentally important ambient temperatures. The conformational space of the compounds was examined using density functional theory (DFT) calculations, and the ideal-gas thermodynamic properties were subsequently calculated using statistical thermodynamics. A consistent thermodynamic description is presented, which was developed using the method of simultaneous correlation that processes experimental data on phase behavior, vapor pressures, and condensed phase heat capacities together with calculated ideal-gas heat capacities. The influence of the position of the hydroxyl group on the thermodynamic properties is discussed and rationalized.

Vapor pressure and thermophysical properties of explosive taggants

Knowledge of the vapor pressure is one of the key parameters that determine the application of detection taggants for a given explosive and useful lifetime. The objective of this work was to determine the vapor pressures and thermodynamically linked properties of selected explosive taggants, namely 2,3-dimethyl-2,3-dinitrobutane, 2-nitrotoluene, and 4-nitrotoluene. Experimental studies included vapor pressure measurements using a static method, investigation of phase behavior by differential scanning calorimetry, and measurement of condensed-phase heat capacities. On the basis of the above-mentioned data and in combination with theoretically calculated ideal-gas thermodynamic properties, the recommended vapor pressure equations for the explosive taggants in a wide temperature range were developed by the method of simultaneous correlation of vapor pressures and thermodynamically linked properties.

Heat capacities of selected active pharmaceutical ingredients

Condensed-phase heat capacities of selected pharmaceutical active pharmaceutical ingredients (APIs), namely (RS)-ibuprofen (CAS RN: 15687-27-1), (S)-ibuprofen (CAS RN: 51146-56-6), (S)-naproxen (CAS RN: 22204-53-1), indomethacin (CAS RN: 53-86-1), and carbamazepine (CAS RN: 298-46-4), were determined using Tian-Calvet calorimetry and power-compensated differential scanning calorimetry in the temperature range 216 to 471 K. In most cases, previously published heat capacities of the studied APIs are in significant disagreement both with each other and our measurements. By analyzing the literature values, many previously published data sets were shown to be erroneous. The heat capacities of supercooled liquid, an important parameter in the modeling of API solubility, were also measured in a wide temperature range when feasible. The phase behavior study of carbamazepine suggests that its thermal stability is lower than previously thought, which is in accordance with the most recent studies on carbamazepine decomposition. This work significantly extends the availability of reliable API heat capacity data for clearly defined polymorphic forms and liquid phase.

Thermodynamic study of acetamides

An extensive thermodynamic study of acetamide and its derivatives, N-methylacetamide, and N,N-dimethylacetamide, is presented in this work. Phase behavior was investigated by a heat-flux differential scanning calorimetry (DSC) from 183 K confirming the previously reported polymorphism of acetamide and N-methylacetamide. Two different polymorphic forms of N,N-dimethylacetamide were observed for the first time. Two static apparatus were employed for the vapor pressure measurements over a wide temperature range focusing on the ambient temperatures. Vapor pressures of metastable phase of acetamide were determined for the first time. Heat capacities of liquid and crystalline phases were measured by Tian-Calvet calorimetry at temperatures between 265 and 355 K. The ideal-gas thermodynamic properties were calculated using a combination of the density functional theory (DFT) and statistical thermodynamics. A consistent thermodynamic description was developed using the method of simultaneous correlation, where the experimental data for phase behavior, vapor pressures, and condensed phase heat capacities and calculated ideal-gas heat capacities are treated together to ensure overall thermodynamic consistency of the results. The observed trends in the thermodynamic properties of liquid phase were rationalized based on molecular interactions.

Thermodynamic study of selected monoterpenes IV

An extensive thermodynamic study of three monoterpenes, (−)-menthone, (+)-pulegone, and (−)-isopulegol, is presented in this work. Phase behaviour was investigated by a heat-flux differential scanning calorimetry (DSC) from 183 K resulting in detection of polymorphic behaviour of (−)-isopulegol and a noticeably slow crystallization of (+)-pulegone. Two static apparatus were employed for the vapour pressure measurements over a wide temperature range including environmentally important ambient temperatures. Heat capacities of liquid phase were measured by Tian-Calvet calorimetry at temperatures between 266 K and 353 K. Conformational space of the compounds was examined using the density functional theory (DFT) calculations and the ideal-gas thermodynamic properties were subsequently calculated using statistical thermodynamics. A consistent thermodynamic description was developed using the method of simultaneous correlation, where the experimental data for phase behaviour, vapour pressures, and condensed phase heat capacities and calculated ideal-gas heat capacities are treated together.

Polymorphism and thermophysical properties of l- and dl-menthol

The thermodynamic properties, phase behaviour, and kinetics of polymorphic transformations of racemic (dl-) and enantiopure (l-) menthol were studied using a combination of advanced experimental techniques, including static vapour pressure measurements, adiabatic calorimetry, Tian-Calvet calorimetry, differential scanning calorimetry (DSC), and variable-temperature X-ray powder diffraction. Several concomitant polymorphs (α, β, γ, and δ forms) were observed and studied. A continuous transformation to the stable α form was detected by DSC and monitored in detail using X-ray powder diffraction. A long-term coexistence of the stable crystalline form with the liquid phase was observed. The vapour pressure measurements of both compounds were performed using two static apparatus over a temperature range from 274 K to 363 K. Condensed-phase heat capacities were measured by adiabatic and Tian-Calvet calorimetry in the wide temperature interval from 5 K to 368 K. Experimental data of l- and dl-menthol are compared mutually as well as with available literature results. The thermodynamic functions of crystalline and liquid l-menthol between 0 K and 370 K were calculated from the calorimetric results. The thermodynamic properties in the ideal-gas state were obtained by combining statistical thermodynamics and quantum chemical calculations based on a thorough conformational analysis. Calculated ideal-gas heat capacities and experimental data on vapour pressure and condensed-phase heat capacity were treated simultaneously to obtain a consistent thermodynamic description. Based on the obtained results, the phase diagrams of l-menthol and dl-menthol were suggested.

Vapor Pressures and Thermophysical Properties of Ethylene Carbonate, Propylene Carbonate, γ-Valerolactone, and γ-Butyrolactone

In this work, a thermodynamic study of four important industrial solvents, ethylene carbonate (CAS RN: 96-49-1), propylene carbonate (CAS RN: 108-32-7), γ-valerolactone (CAS RN: 108-29-2), and γ-butyrolactone (CAS RN: 96-48-0), is presented. The vapor pressure measurements were performed by static method using two apparatuses in a combined temperature interval (238–363) K. Heat capacities of condensed phases were measured by Tian–Calvet calorimetry in the temperature interval (262–358) K. The phase behavior of ethylene carbonate and γ-valerolactone was investigated by a heat-flux DSC from 183–303 and 328 K, respectively. Ideal-gas thermodynamic properties were calculated using the methods of statistical thermodynamics based on calculated fundamental vibrational frequencies and molecular structure data. A consistent thermodynamic description of all involved properties (calculated ideal-gas heat capacities and experimental data on vapor pressures, condensed phase heat capacities, and vaporization enthalpies...

Vapor Pressures and Thermophysical Properties of Dimethyl Carbonate, Diethyl Carbonate, and Dipropyl Carbonate

In this work, a thermodynamic study of important industrial solvents, dimethyl carbonate (CAS RN: 616-38-6), diethyl carbonate (CAS RN: 105-58-8), and dipropyl carbonate (CAS RN: 623-96-1), is presented. The vapor pressure pressure measurements were performed using the static method in the temperature interval 238–308 K. Heat capacities of condensed phases were measured by Tian–Calvet calorimetry in the temperature interval 260–358 K. The phase behavior was investigated by DSC in the temperature interval 183–300 K. The thermodynamic properties in the ideal gaseous state were calculated using the methods of statistical thermodynamics based on calculated fundamental vibrational frequencies and molecular structure data. Calculated ideal-gas heat capacities and experimental data on vapor pressures, condensed phase heat capacities, and vaporization enthalpies were treated simultaneously to obtain a consistent thermodynamic description.

Vapor pressures and thermophysical properties of selected monoterpenoids

A thermodynamic study of selected monoterpenoids, geraniol, β-citronellol, and borneol, is presented in this work. The vapor pressure measurements were performed using two static apparatus over a wide temperature range from 273 to 363K. Liquid heat capacities were measured by Tian–Calvet calorimetry in the temperature interval from 258 to 355K. The phase behavior was investigated by DSC from 183K. The thermodynamic properties in the ideal-gas state were calculated by combining statistical thermodynamics and density functional theory (DFT) calculations. Calculated ideal-gas heat capacities and experimental data on vapor pressure and condensed phase heat capacity were treated simultaneously to obtain a consistent thermodynamic description.

Vapor pressures and thermophysical properties of selected hexenols and recommended vapor pressure for hexan-1-ol

A thermodynamic study of selected unsaturated alcohols, cis-hex-3-en-1-ol, trans-hex-2-en-1-ol, and hex-1-en-3-ol, together with hexan-1-ol, is presented in this work. The vapor pressure measurements were performed using the static method over the environmentally important temperature range from 238 to 308K. Liquid heat capacities were measured by Tian–Calvet calorimetry in the temperature interval from 258 to 355K and were extended by controlled extrapolation by differential scanning calorimetry (DSC) toward the normal boiling point temperatures. The phase behavior was investigated by DSC from 183K. The thermodynamic properties in the ideal-gas state were calculated by combining statistical thermodynamics and density functional theory (DFT) calculations. Scaling factors were evaluated based on measured Raman and IR spectra. Calculated ideal-gas heat capacities and experimental data on vapor pressures, condensed phase heat capacities, and vaporization enthalpies were treated simultaneously to obtain a consistent thermodynamic description.

Thermodynamic study of selected monoterpenes III

A thermodynamic study of selected monoterpenes, (−)-trans-pinane, (+)-Δ-carene, eucalyptol, (+)-limonene, and (−)-limonene, is presented in this work. The vapor pressure measurements were performed using the static method over the environmentally important temperature range (238 to 308)K. Liquid heat capacities were measured by Tian–Calvet calorimetry in the temperature interval (258 to 355)K. The phase behavior was investigated by differential scanning calorimetry (DSC) from T=183K. The thermodynamic properties in the ideal-gas state were calculated by combining statistical thermodynamic and density functional theory (DFT) calculations. Calculated ideal-gas heat capacities and experimental data for vapor pressures and condensed phase heat capacities were treated simultaneously to obtain a consistent thermodynamic description.

Thermodynamic study of alkane-α,ω-diamines – Evidence of odd–even pattern of sublimation properties

Calculated ideal-gas heat capacities and experimental data for vapor pressure, condensed phase heat capacities, and calorimetric vaporization enthalpies of alkane-α,ω-diamines, NH2-(CH2)n-NH2 (2≤n≤8), were treated simultaneously to obtain a consistent thermodynamic description. Vapor pressures for the members with 3≤n≤8 were measured using the static method in the temperature range from 233 to 314K. The thermodynamic properties in the ideal gaseous state for the members with n=2 and 3 were obtained using the fundamental vibrational frequencies, molecular structure data, and potential energy profiles of internal rotations calculated using the density functional theory (DFT) at the B3LYP/6-311+G(d,p) level of theory and four statistical thermodynamic models of different complexity. Based on the results of the simultaneous correlation, the sublimation and vaporization thermodynamic properties for 2≤n≤8 and the triple-point coordinates for n=3, 4, 5 and 7 were calculated. The thermodynamic properties for liquid–vapor equilibrium display a linear dependence on number of methylene groups n while the sublimation thermodynamic properties show an evident odd–even effect with higher values for even members of a homologous series. The alternating pattern is interpreted on the basis of the literature crystallographic data and corresponding intermolecular interactions. Based on the observed trends, the correlations allowing the prediction of the thermodynamic properties for the crystal–vapor and liquid–vapor equilibria and crystalline and ideal-gas heat capacities within the homologous series are suggested.

Thermodynamic study of selected monoterpenes II

A thermodynamic study of selected monoterpenes, (−)-borneol, (−)-camphor, (±)-camphene, and (+)-fenchone is presented in this work. The vapor pressure measurements were performed using the static method over the environmentally important temperature range from (238 to 308)K. Heat capacities of condensed phases were measured by Tian–Calvet calorimetry in the temperature interval from (258 to 355)K. The phase behavior was investigated by differential scanning calorimetry (DSC) from subambient temperatures up to the fusion temperatures. The thermodynamic properties in the ideal-gas state were calculated by combining statistical thermodynamic and density functional theory (DFT) calculations. Calculated ideal-gas heat capacities and experimental data for vapor pressures and condensed phase heat capacities were treated simultaneously to obtain a consistent thermodynamic description.

Two semiempirical expressions for condensed-phase heat capacities

We propose two semiempirical expressions for representing condensed-phase heat capacities over a wide temperature range. Both can be integrated analytically to give closed-form expressions for entropies and enthalpies. As examples, we use the expressions to represent the molar heat capacities, entropies, and enthalpies of 〈Si〉 and 〈Al〉.

Propriétés thermodynamiques en phase condensée des ortho, méta et para fluorotoluéne, crésol et toluidine

The fusion thermodynamic properties and condensed phase heat capacities for isomers of fluorotoluene, cresol and toluidine were determined using microcalorimetry. The lower melting points and enthalpies of fusion for the meta isomer are explained by the lower strength of intermolecular hydrogen bonds. The increase in heat capacity in the liquid state and greater significance of the fusion heat capacities for cresol and toluidine indicate molecular association in these compounds.

ChemInform Abstract: Condensed‐Phase Heat Capacities and Derived Thermodynamic Properties for 1,4‐Dimethylbenzene, 1,2‐Diphenylethane, and 2,3‐Dimethylnaphthalene

Abstract Condensed-phase heat capacities and enthalpies were determined at temperatures from 10 to near 400 K for 1,4-dimethylbenzene, 1,2-diphenylethane, and 2,3-dimethylnaphthalene, and were used to provide values of enthalpies, entropies, and heat capacities at vapor saturation. Enthalpies and entropies for the ideal-gas state were determined at selected temperatures with available vapor pressures and enthalpies of vaporization. The enthalpies, entropies, and Gibbs energies of formation, also at selected temperatures, were derived for the ideal-gas state with available enthalpies of combustion.

ChemInform Abstract: Condensed‐Phase Heat‐Capacity Studies and Derived Thermodynamic Properties for Six Cyclic Nitrogen Compounds.

Abstract Condensed-phase heat capacities and enthalpies were determined at temperatures from near 10 to 400 K for N-methylpyrrole, 2,5-dimethylpyrrole, piperidine, 2-methylpiperidine, 4-methylpyridine, and N-methylcarbazole, and were used to provide the Gibbs energy, enthalpy, entropy, and heat capacity along the vapor-saturation line at temperatures from 0 to 400 K. The corresponding ideal-gas thermodynamic properties were derived using available vapor pressures and enthalpies of vaporization. The Gibbs energy, enthalpy, and entropy of formation were derived for the ideal gas at selected temperatures with available enthalpies of combustion.

Condensed-phase heat capacities and derived thermodynamic properties for 1,4-dimethylbenzene, 1,2-diphenylethane, and 2,3-dimethylnaphthalene

Condensed-phase heat capacities and enthalpies were determined at temperatures from 10 to near 400 K for 1,4-dimethylbenzene, 1,2-diphenylethane, and 2,3-dimethylnaphthalene, and were used to provide values of enthalpies, entropies, and heat capacities at vapor saturation. Enthalpies and entropies for the ideal-gas state were determined at selected temperatures with available vapor pressures and enthalpies of vaporization. The enthalpies, entropies, and Gibbs energies of formation, also at selected temperatures, were derived for the ideal-gas state with available enthalpies of combustion.