Heat capacity and decomposition of rimantadine hydrochloride.

Heat capacities of the antiviral drug rimantadine hydrochloride in the crystalline state were measured by adiabatic calorimetry and differential scanning calorimetry in the temperature range from (7 to 453) K. A broad low-enthalpy solid-state phase anomaly was detected between (170 and 250) K. Thermodynamic functions for crystalline rimantadine hydrochloride were derived. Decomposition of the studied compound was probed by the Knudsen effusion method and thermogravimetry with the support of quantum chemical calculations. The enthalpy of decomposition of rimantadine hydrochloride into the corresponding amine and hydrogen chloride was estimated from those data. The thermodynamic functions of the corresponding amine in the ideal gaseous state, including enthalpy of formation, were obtained using statistical thermodynamics with the necessary molecular parameters computed using quantum chemical methods. The enthalpy of formation of crystalline rimantadine hydrochloride was estimated.

Thermodynamic behavior and polymorphism of 1-butyl-3-methylimidazolium hexafluorophosphate composites with multiwalled carbon nanotubes.

Based on room-temperature densities measured in this research for ionic nanofluids (INFs) with four ionic liquids (ILs), we conclude that evacuation is a necessary step to maximize the IL penetration into multiwalled carbon nanotubes (MWCNT). An improved procedure for reproducible preparation of INFs is proposed. Thermal behavior of five (1-butyl-3-methylimidazolium hexafluorophosphate + MWCNT) samples was studied by adiabatic calorimetry over the temperature range (78 to 370) K. The samples contained from 0.11 to 0.92 mass fraction of the nanophase. Their appearance changed from the fluid to the powder with increasing the MWCNT content. For the fluid samples, the specific heat capacity was found be an additive quantity of the specific heat capacities of the components for the crystal and liquid phases, and the temperatures of phase transitions did not change relative to the bulk values. For the powder-like sample with the highest IL content, a sigmoidal heat capacity curve was observed. Thus, the internal diameter of the studied MWCNT was small enough to switch from the isothermal melting process to the gradual transition from the crystal-like structures to the liquid-like ones.

Polymorphism and thermophysical properties of L- and DL-menthol.

The thermodynamic properties, phase behavior, and kinetics of polymorphic transformations of racemic (DL-) and enantiopure (L-) menthol were studied using a combination of advanced experimental techniques, including static vapor pressure measurements, adiabatic calorimetry, Tian-Calvet calorimetry, differential scanning calorimetry (DSC), and variable-temperature X-ray powder diffraction. Several concomitant polymorphs (α, ß, 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 vapor 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 vapor 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.

Thermodynamic Properties of Organic Substances: Experiment, Modeling, and Technological Applications.

In this review, results of the studies of thermodynamic properties of organic substances conducted at the Chemistry Department of the Belarusian State University (Minsk, Belarus) over a period of more than 50 years are summarized. Emphasis is made on precise measurements (both calorimetry and equilibria) and prediction methods, including group-contribution, quantum chemical, and statistical mechanical, for a broad range of thermodynamic properties of various classes of chemical substances. The principal purposes of these studies were to establish relationships between thermodynamic properties of organic substances and their molecular structure, develop methods of extrapolation and prediction of the properties of substances lacking experimental data, and provide thermodynamic background for innovative energy- and resource-saving technologies.

Thermodynamic properties of adamantane revisited.

The heat capacity and parameters of the solid-to-solid phase transition of adamantane were measured in the temperature range from 80 to 370 K by use of adiabatic calorimetry. The thermodynamic functions for the compound in the crystalline and liquid states were calculated. The standard molar enthalpy of formation in the crystalline state for adamantane was obtained from combustion calorimetry by use of two different calorimeters. Available data on the enthalpy of combustion, saturated vapor pressure, and enthalpy of sublimation of adamantane were collected, analyzed, and selected. On the basis of spectroscopic data and results of quantum-chemical calculations, the ideal-gas properties for adamantane were calculated by a statistical thermodynamics method.

Thermodynamics of ionic liquids precursors: 1-methylimidazole.

The standard molar enthalpy of formation in the liquid state for 1-methylimidazole (MeIm) was obtained from combustion calorimetry. The enthalpy of vaporization of the compound was derived from the temperature dependence of the vapor pressure measured by the transpiration method. Additionally, the enthalpy of vaporization for MeIm was measured directly using Calvet-type calorimetry. In order to verify the experimental data, first-principles calculations of MeIm were performed. The enthalpy of formation evaluated at the G3MP2 level of theory is in excellent agreement with the experimental value. The heat capacity and parameters of fusion of MeIm were measured in the temperature range (5 to 370) K using adiabatic calorimetry. The thermodynamic functions for the compound in the crystal and liquid states were calculated from these data. Based on the experimental spectroscopic data and the results of quantum-chemical calculations, the ideal-gas properties for MeIm were calculated by methods of statistical thermodynamics.

Calorimetric determination of the enthalpy of 1-butyl-3-methylimidazolium bromide synthesis: a key quantity in thermodynamics of ionic liquids.

The enthalpy of the 1-butyl-3-methylimidazolium bromide [C(4)mim]Br ionic liquid synthesis reaction 1-methylimidazole (liq) + 1-bromobutane (liq) --> [C(4)mim]Br (liq) was determined in a homemade small-volume isoperibol calorimeter to be Delta(r)H degrees (298) = -87.7 +/- 1.6 kJ x mol(-1). The activation energy for this reaction in a homogeneous system E(A) = 73 +/- 4 kJ x mol(-1) was found from the results of calorimetric measurements. The formation enthalpies for the crystalline and liquid [C(4)mim]Br were determined from the calorimetric data: Delta(f)H degrees (298)(cr) = -178 +/- 5 kJ x mol(-1) and Delta(f)H degrees (298)(liq) = -158 +/- 5 kJ x mol(-1). The ideal-gas formation enthalpy of this compound Delta(f)H degrees (298)(g) = 16 +/- 7 kJ x mol(-1) was calculated using the methods of quantum chemistry and statistical thermodynamics. The vaporization enthalpy of [C(4)mim]Br, Delta(vap)H degrees (298) = 174 +/- 9 kJ x mol(-1), was estimated from the experimental and calculated formation enthalpies. It was demonstrated that vapor pressure of this ionic liquid cannot be experimentally determined.

Physicochemical properties, structure, and conformations of 1-Butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4mim]NTf2 ionic liquid.

Thermodynamic properties of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4mim]NTf2) ionic liquid have been studied by adiabatic calorimetry in the temperature range of 5 to 370 K. This compound has been found to form crystal, liquid, and glass. The temperature and enthalpy of fusion for [C(4)mim]NTf(2) have been determined to be T(fus) = 270.22 +/- 0.02 K and Delta(fus)H = 23.78 +/- 0.04 kJ.mol(-1), respectively. The heat capacity of crystalline [C(4)mim]NTf(2) in the T range of 205 to 255 K may vary by a few percent, subject to the procedure of the crystal preparation. The glass transition temperature for [C(4)mim]NTf(2) has been found to be T(g) = 181.5 +/- 0.1 K. On the basis of the results of DFT quantum chemical calculations, the experimental vibrational spectra, and the available literature data, thermodynamic properties of [C(4)mim]NTf(2) in the ideal-gas state have been calculated by the statistical thermodynamic methods. The entropy values for the gaseous compound obtained from the experimental data and the calculations are in satisfactory agreement.