Andrey V. Blokhin

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.

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 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.

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.

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.

Heat capacities and enthalpies of transitions of 1-methylcyclopentanol and 1-chloro-1-methylcyclopentane in the condensed state

Abstract Heat capacities and enthalpies of transitions for 1-methylcyclopentanol (I) and 1-chloro-1-methylcyclopentane (II) in the condensed state were measured by vacuum adiabatic calorimetry in interval from 5 to 315 K. It was found that these compounds formed glasses by their cooling from 310 K at a rate (0.03–0.05) K·s−1. The crystal I undergoes two solid-to-solid transitions at 281.72 K and 301.47 K and melts at 308.53 K. The correlation between the entropies of transitions of I testifies that it does not form the plastic crystal phase. Two solid-to-solid transitions at 164.20 K and 178.82 K occurred in the crystal II. The fusion temperature of II is 189.05 K. The ratio of the entropy of transition crII → crI to that of fusion for II exceeds 8. This fact confirms that II forms the plastic crystal state even in a very narrow interval from 178.82 to 189.05 K. The thermodynamic characteristics of glassy I and II were obtained and the thermodynamic analysis of the heat capacity jump at Tg and the residual entropies was made for both compounds on the base of possible structural changes of molecules and substances at Tg.

Thermodynamic properties of cellulose of various structures in the temperature range 5–370 K

The energies of combustion of cellulose samples with different supramolecular structures were determined, and the enthalpies of formation of these substances were calculated. Reliable values of the heat capacity were obtained.

Thermodynamic properties of 1-methylcyclopentanol and 1-chloro-1-methylcyclopentane in the ideal gas state

Abstract The enthalpies of evaporation, the saturated vapor pressures of 1-methylcyclopentanol (I) and 1-chloro-1-methylcyclopentane (II) and the energy of combustion of crystal I were measured. IR and Raman spectra of both compounds were recorded and vibrational analyses were made. Thermodynamic functions of I and II in the ideal gas state were calculated by the statistical thermodynamics methods. In order that the experimental and calculated entropies of gaseous 1,1-ClMeCP agree, it is necessary to determine the contribution of pseudorotation as the contribution of motion with potential function V ( o ) = 5800 − 3060 cos( o ) − 2740 cos(2 o ) J mol −1 and pseudorotational moment of inertia 15.24 × 10 −40 g cm 2 . The molecular rotation in the plastic crystal state of II is discussed.