A.I. Druzhinina

Heat capacity, saturation vapor pressure, and thermodynamic functions of ethyl esters of C3–C5 and C18 carboxylic acids

The heat capacities of ethyl propanoate (EPr), ethyl n-pentanoate (EPen), and ethyl n-octadecanoate (ethyl stearate, ESt) were measured by vacuum adiabatic calorimetry in the temperature range of 6 to 373 K. Triple point temperatures, fusion enthalpies and entropies, and purity of the samples of the sub-stances under study were determined. The saturation vapor pressures for EPr and EPen were determined by comparative ebulliometry in an atmospheric pressure range of 4.0 to 101.7 kPa. The normal boiling points and vaporization enthalpies vs. temperature were obtained. The standard thermodynamic functions (S, H, and G) were calculated for the condensed and ideal gas states on the basis of the experimental data. The vapor pressures of the atmospheric range were extrapolated to entire ranges of the liquid phases of EPr and EPen using the principle of corresponding states and the combined processing of pT parameters and low-temperature differences in the heat capacities of an ideal gas and liquid.

Low-temperature heat capacity and thermodynamic properties of 1,1,1-trifluoro-2,2-dichloroethane

The heat capacity of Freon R-123, CF 3 CHCl 2 , was measured by adiabatic calorimetry over the temperature range 8.55-297.52 K. The temperature of the λ-anomaly, T trs = 125.5 ± 0.1 K. the triple point temperature, T tp = 145.68 ± 0.02 K, and the enthalpy and entropy of fusion, Δ fus H m =5.51 ± 0.01 kJ mol -1 and Δ fus S m = 37.83 ± 0.05 J mol -1 K -1 were determined. The main thermodynamic functions of CF 3 CHCl 2 : S o m (T), (H o m (T) - H o m (0)), and (G o m (T)-H o m (0)) were calculated at T = 298.15 K. The low-temperature differences between the heat capacities of ideal gas and liquid, ΔC p,m = C o p,m (g) - C p,m (1), were used for simultaneous treatment with the saturated vapor pressure data of R-123 [Int. J. Thermophys. 13 (1992)999], which had been measured from 256.4 to 453.8 K, in order to extrapolate the saturation vapor pressure from T = 256 K down to T 1p .

Thermodynamics of vaporization of some cyclic perfluorocarbons

The temperature dependence of the saturation vapor pressure of perfluoro-meta-dimethylcyclohexane, (CF3)2C6F10, has been determined by the ebulliometric method in the moderate pressure range from 8.4 to 101.6 kPa. Enthalpies of vaporization have been obtained calorimetrically for perfluorobicyclo(4,4,0)dec(1,6)ene, C10F16, and (CF3)2C6F10 at T = 298.15 K. Densities of C10F16 have been measured in the small temperature range from 293 to 338 K. Critical parameters have been estimated from vapor pressure data and densities for the substances under study and for some mono- and bicyclo-perfluorocarbons investigated earlier. A second-order group additivity method has been applied to predict the vaporization enthalpies of some cyclic perfluorocarbons.

The thermodynamic characteristics of ferrocene alkyl and acyl derivatives

The heat capacity of iso-butylferrocene C5H5FeC5H4-C4H9-i was measured over the temperature range 7–372 K in an adiabatic vacuum calorimeter. Substance purity and the thermodynamic characteristics of fusion (temperature, enthalpy, and entropy) were determined. Saturated vapor pressures and the enthalpies of vaporization of n-propylferrocene C5H5FeC5H4-C3H7-n, propionylferrocene C5H5FeC5H4-COC2H5, and iso-butylferrocene were measured by the dynamic method of substance transfer in an inert gas flow. The entropy, enthalpy, and Gibbs energy of the substances in the ideal gas state at 298.15 K were calculated. The thermodynamic values obtained in this work and reported in the literature for ferrocene alkyl and acyl derivatives were critically analyzed. The mutual consistency of the data on both homologous series was checked.

Heat Capacity and Thermodynamic Functions of 4,4 '-Dimethylbiphenyl and 4,4 '-Di-tert-butylbiphenyl

The heat capacity (Cp m) of 4,4′-dimethylbiphenyl and 4,4′-di-tert-butylbiphenyl in the temperature range of 8—373 K was measured by low-temperat ure adiabatic calorimetry, and thermodynamic characteristics of the solid-phase transitions of 4,4′-d i-tert-butylbiphenyl were determined. Temperatures, enthalpies, entropies of melting, and the purity of the samples of the tested substances were determined by means of differential scanning calorimetry. The main thermodynamic functions of the substances in the condensed state at 298 K were calculated.

Thermodynamic functions of buthylderivatives of ferrocene

The heat capacity of isobuthanoylferrocene, C5H5FeC5H4-COCH(CH3)2, was measured by low-temperature adiabatic calorimetry. The purity, temperature, and enthalpy of fusion were obtained. The ideal gas thermodynamic functions were derived at T = 298.15 K. The purity and thermodynamic functions of fusion of isobuthylferrocene, C5H5FeC5H4-CH2CH(CH3)2, were obtained by differential scanning calorimetry. The sample was synthesized by the reduction of isobuthanoylferrocene obtained by the direct acylation of ferrocene.

The low-temperature heat capacity and saturation vapor pressure of ethyl ester of butanoic acid

The heat capacity, thermodynamic properties of fusion, and purity of the ethyl ester of butanoic acid were determined by adiabatic calorimetry in the temperature range from 8 to 372 K. The pT-parameters of the ester for the equilibrium liquid-vapor were measured by comparative ebulliometry in the “atmospheric” range of pressure from 10.8 to 101.7 kPa. The obtained data were used to derive the normal boiling temperature (Tn.b), the enthalpies of vaporization at T = 298.15 K and Tn.b, and the main thermodynamic functions (changes of S, H, G) in the crystal and liquid states of the temperature interval studied and in the ideal gas state at T = 298.15 K. The experimental vapor pressures of the narrow temperature interval, ΔT = 62 K were extended to the entire range of the liquid, Tcr − Ttp0 = 394.3 K, from the triple, Ttp0, to the critical, Tcr, temperatures.

Determination of saturated vapor pressure of organic substances from the triple to critical point

Methods are given of extrapolating the saturated vapor pressure of substances of “atmospheric range” to the entire liquid phase region from the triple to critical point. The extrapolation of the pT parameters from room temperature to the triple point is performed by simultaneous processing of vapor pressure and of differences between the heat capacities of ideal gas and liquid. The liquid-vapor equilibrium in the region from the normal boiling temperature to the critical point is predicted by the law of corresponding states of L.P. Filippov using the experimentally obtained pT data and values of density of liquids. Experimental facilities are described for determining the saturated vapor pressure by the comparison ebulliometric method and for determining the low-temperature heat capacity by the vacuum adiabatic calorimetry. The methods of extrapolating the vapor pressure are tested with standard substances for which reliable pT data are available for the entire liquid phase region.

The Temperature Dependences of Saturated Vapor Pressures and Heat Capacities of Some Perfluoropolyethers

The borling temperatures of perfluoro-2,4,6,9,11,13-hexaoxy-n-tetradecane, perfluoro-2,4,6,8,11,13,15,17-octaoxy-n-octadecane, and perfluoro-2,4,6,8,11,13,15,17,19,21-decaoxy-n-docosane were determined by comparative ebulliometry over the saturated vapor pressure range 6.2–101.6 kPa. The heat capacity of perfluoro-2,4,6,8,11,13,15,17-octaoxy-n-octadecane was studied by adiabatic calorimetry over the temperature range 5.3–371.2 K. The densities of the substances at 296–338 K were measured in quartz pycnometers. The data obtained were used to calculate the normal boiling points, enthalpies of vaporization, critical parameters, and thermodynamic functions (entropy, enthalpy, and Gibbs energy) of the polyethers studied.

Heat capacity and thermodynamic functions of 2-methylbiphenyl and 3,3′-dimethylbiphenyl in the range of 6 to 372 K

The heat capacities of 2-methylbiphenyl and 3,3′-dimethylbiphenyl are measured by means of low-temperature adiabatic calorimetry in the temperature range of 6 to 372 K. The thermodynamic characteristics of fusion and the glass transition of the investigated compounds are determined. The saturation vapor pressure and enthalpy of vaporization of 3,3′-dimethylbiphenyl are determined according to the dynamic method based on the transfer of a substance vapor in a helium flow. The absolute entropies and changes in Gibbs energies of biphenyl derivatives are calculated from the data obtained in the condensed and ideal gas states. The contribution of the Cb-(Cb) group is determined using the Benson additive method for calculating the absolute entropies of biphenyl derivatives in the liquid state (where Cb is the carbon atom in a benzene ring).