Gennady J. Kabo

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.

IR and X-ray Study of Polymorphism in 1-Alkyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imides

The crystal structure of [C(n)mim]NTf(2) (n = 2, 4, 6) was studied for the first time simultaneously by X-ray diffraction method and IR spectroscopy. The temperature-dependent IR spectrum for crystalline [C(4)mim]NTf(2) was demonstrated to correlate with both the X-ray data and the calorimetric results obtained earlier. Therefore, it was found that IR spectroscopy is able to establish the correspondence between the X-ray and the calorimetric data in this case. The joint use of X-ray diffraction, IR spectroscopy, and quantum-chemical calculations allowed us to determine the structure of all [C(2)mim]NTf(2) crystalline modifications obtained earlier by adiabatic calorimetry measurements. Thus, a new approach for the future identification of ionic liquid crystal structure by use of temperature-dependent infrared spectroscopy is suggested and justified.

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.

Structure, conformations, vibrations, and ideal-gas properties of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic pairs and constituent ions.

Energies, geometries, and frequencies of normal vibrations have been calculated by quantum-chemical methods for different conformers of a bis(trifluoromethylsulfonyl)imide anion (NTf2-), 1-alkyl-3-methylimidazolium cations ([C(n)mim]+, n = 2, 4, 6, 8), and [C(n)mim]NTf2 ionic pairs. The assignment of frequencies for NTf2-, [C2mim]+, and [C4mim]+ in the vibrational spectra of ionic liquids have been performed. Thermodynamic properties of [C(n)mim]NTf2, [C(n)mim]+, and NTf2- in the gas state have been calculated by the statistical thermodynamic methods. The resulting entropies are in satisfactory agreement with the values obtained from the experimental data previously reported in literature.

Thermodynamic properties of adamantane and the energy states of molecules in plastic crystals for some cage hydrocarbons

Thermodynamic properties of adamantane (I) were investigated in this paper. Heat capacities of I in the condensed state between 340 and 600 K were measured by a scanning calorimeter of triple heat bridge type, and characteristics of the fusion of I were determined. The measurements of the enthalpy of sublimation and the saturated vapor pressure for I were made. Thermodynamic functions of I in the ideal gas state were calculated by the statistical thermodynamics methods. The energy states of molecules in the plastic crystals for some cage hydrocarbons (adamantane, bicyclo[2.2.2]octane, pentacycloundecane, heptacyclotetradecane and diamantane) are discussed.

Thermodynamic properties of 6-aminohexanoic lactam (ɛ-caprolactam)

The heat capacities of crystalline and liquid ɛ-caprolactam at the temperatures 5 K to 90 K and 340 K to 520 K were measured by vacuum adiabatic calorimetry and the triple heat-bridge method. The enthalpy of sublimation of ɛ-caprolactam was directly determined by a heat-conduction differential calorimeter: Δ sub H o m (338 K) = (86.30±0.22) kJ · mol −1 . The saturated vapour pressure of solid ɛ-caprolactam in the temperature range: 330 K to 340 K was measured by the integral effusion Knudsen method: ln( p /Pa) = (34.652±0.305)−(10741±98)(K/ T ), and the sublimation enthalpy value at the middle temperature of the measurements was calculated Δ sub H o m (320 K) = (89.3±0.8) kJ · mol −1 . Using these and literature values two values were obtained of the conventional molar entropy of gaseous ɛ-caprolactam: S o m (g, 320 K) = (377.0±2.6) J · K −1 · mol −1 and S o m (g, 320,K) = (369.2±1.0) J · K −1 · mol −1 , the discrepancy in which was caused by the difference in the sublimation-enthalpy values, obtained by calorimetric and effusion measurements. An isothermally jacketed calorimeter was used to measure the energy of combustion of ɛ-caprolactam: Δ c H o m (cr, 298.15 K) = −(3603,76±1.46) kJ · mol −1 . The vibrational spectra were estimated from the infrared and Raman spectra and as a result vibrational assignments for ɛ-caprolactam were made. Statistical calculation of the thermodynamic properties of ɛ-caprolactam in the ideal-gas state was carried out with an account of the contributions of four energy-non-equivalent conformations. The statistically calculated molar entropy: S o m (g, 320 K) = 374.25 J · K −1 · mol −1 is in satisfactory agreement with the experimental values. Thermodynamic properties of ɛ-caprolactam in the condensed state (0 to 550 K) and in the ideal-gas state (100 K to 1000 K) were calculated and tabulated.

The effect of the failure of isotropy of a gas in an effusion cell on the vapor pressure and enthalpy of sublimation for alkyl derivatives of carbamide

Abstract The divergence of the values of enthalpy of sublimation for urea, methylurea, ethylurea, 1,1-dimethylurea, 1,3-dimethylurea, (1-methylethyl)urea, n -butylurea, (1-methylpropyl)urea, (1,1-methylethyl)urea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis(1,1-dimethylethyl)urea obtained calorimetrically and from the effusion measurements [Izv. Akad. Nauk SSSR. Ser. Khim. 4 (1990) 750] was analyzed. The results of the calorimetric measurements were shown to be independent of the evaporation rate. The influence of the isotropy failure of a gas on the effusion results was analyzed. The vapor pressures and enthalpies of sublimation were corrected according to the proposed technique. The decrease of divergence of the values of enthalpies of sublimation for alkyl derivatives of carbamide from effusion and calorimetric measurements while taking into account the isotropy failure of a gas was shown. The average weighted value of enthalpy and entropy of sublimation were evaluated. The additive scheme for enthalpy of sublimation was proposed.

Additivity of the enthalpies of formation of urea derivatives in the crystalline state

Abstract An isothermally jacketed calorimeter was used to measure the energies of combustion of methylurea (I), ethylurea (II), 1,1-dimethylurea (III), 1,1-diethylurea (IV), isopropylurea (V), tertbutylurea (VI), 1,3-ditertbutylurea (VII), secbutylurea (VIII), butylurea (IX), tetramethylurea (X), urea (XI), phenylurea (XII), and 1,3-diphenylurea (XIII). Based on experimental enthalpies of combustion the standard molar enthalpies of formation ΔfHmo/(kJ·mol−1) were calculated to be I, −(332.78±0.75); II, −(357.76±0.74); III, −(319.06±0.68); IV, −(372.21±1.13); V, −(389.49±1.27); VI, −(414.73±0.87); VII, −(499.81±4.22); VIII, −(413.23±1.50); IX, −(419.48±3.23); X, −(262.17±1.06); XI, −(333.13±0.69); XII, −(218.57±2.38); and XIII, −(116.83±4.43). The possibility of applying calculation methods to estimate the enthalpies of formation of substituted urea derivatives in the condensed state is analysed and two versions of additive schemes for calculation of ΔfHmo are considered.

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.

Solid Phase Transitions of the Cyclohexane Derivatives and the Model of Energy States of Molecules in Plastic Crystals

Abstract The present paper summarizes the results of the measurements of thermodynamic properties of phase transitions of some cyclohexane derivatives in the condensed state and provides the analysis of the changes of dynamic behaviour of molecules during transitions from rigid crystal to plastic crystalline state. These results are discussed on the basis of the main trends of thermodynamic properties of solid state transitions in the series of the compounds having the similar structure. The analysis of the data obtained allows to develop new concept of energy states of molecules in plastic crystals. The combination of the results of calorimetric and spectral measurements with the data obtained by the method of statistical thermodynamics for the series of cyclohexane derivatives leads to the conclusion of the existence of internal rotation, ring inversion, and rotation of molecules as a whole in the nodes of the plastic crystal lattice.