V.P. Kolesov

The standard enthalpy of formation of 1,2,3,4-tetrachlorodibenzo-p-dioxine

The energy of combustion of crystalline 1,2,3,4-tetrachlorodibenzo-p-dioxine (-5122.9 ± 7.4 kJ/mol) was measured using an isothermic-shell calorimeter with a rotating platinum plated bomb. The result was used to calculate the enthalpy of combustion (-5120.4 ± 7.4 kJ/mol) and formation (−267.8 ± 7.6 kJ/mol) for the crystalline state. The enthalpy of sublimation was measured using a Calvet microcalorimeter at 411.5 K (116.0 ± 2.6 kJ/mol); recalculation to T = 298.15 K gave 118.7 ± 2.6 kJ/mol. The enthalpy of formation of 1,2,3,4-tetrachlorodibenzo-p-dioxine in the gas state was calculated (−149.1 ± 8.0 kJ/mol)

Heat capacity from 12 to 300 K, phase transitions, and thermodynamic functions of 1,1,1-trifluoro-3-chloropropane and 1,1,1,3-tetrachloropropane

Abstract The heat capacity of 1,1,1-trifluoro-3-chloropropane and 1,1,1,3-tetrachloropropane from 12 to 300 K and also the temperature and enthalpy of fusion of these compounds were measured in a vacuum adiabatic calorimeter. The results obtained were used for calculating the thermodynamic functions from 12 to 300 K and, in conjunction with literature data, for calculating ΔG f o (l, 298.15 K). 1,1,1-Trifluoro-3-chloropropane was found to undergo two solid-phase transitions, one transition being monotropic ( T = (116.0 ± 0.1) K; ΔH ′ t = −(605 ± 9) cal th mol −1 ), and the other, enantiotropic ( T = (169.8 ± 0.1) K; ΔH ″ t = (1073 ± 4) cal th mol −1 ). Only one solid-phase transition was found for 1,1,1,3-tetrachloropropane ( T = (219.9 ± 0.1) K; ΔH ″ t = (527 ± 4) cal th mol −1 ). Raman, i.r., and n.q.r. spectra of various phases point to the association of the observed solid-phase transitions with the transformations of conformers.

The order-disorder transitions in some organic crystals

The order-disorder and glass formation processes occurring in some solid organic compounds with cage structures and in some solid halogen-ethanes have been studied by low-temperature calorimetry. The thermodynamic data have been used together with the results of other physicochemical experiments to interpret the molecular processes which occur during the phase transformation.

Heat capacities, phase transitions, and thermodynamic functions of 1,1,2,2-tetrafluoro-1,2-dichloroethane and 1,1,2-trifluoro-1,2,2-trichloroethane

The heat capacities of 1,1,2,2-tetrafluoro-1,2-dichloroethane and 1,1,2-trifluoro-1,2,2-trichloroethane were measured from 8 to 300 K by adiabatic calorimetry and the thermodynamic functions were calculated from the results. Two phase transitions were found in the crystalline CF 2 ClCF 2 Cl. The conclusion was made, using i.r. spectra, that one of them: T ′ tr = (109.3 ± 0.2) K, Δ H ′ tr = (1212 ± 13) J mol −1 , was associated with the conformer transformations and the other: T ″ tr = (134.6 ± 0.1) K, Δ H ″ tr = (2628 ± 3) J mol −1 , with the formation of plastic crystal. Only one solid-phase transition was found in CF 2 ClCFCl 2 : T ″ tr = (82.5 ± 0.5) K, Δ H ″ tr = (830.9 ± 7.9) J mol −1 . This anomaly was probably caused by the onset of axial rotation of the molecules. The zero entropy of CF 2 ClCFCl 2 was found to be equal 10.1 J K −1 mol −1 . An assumption was made that a disorder of crystal II at T = 0 had a conformational nature.

Enthalpy of formation of trifluorochloroethene

Abstract The standard molar enthalpy of formation of CF2 = CFCl(g) at 298.15 K derived from new measurements of the energy of combustion of liquid samples of the substance is − (505.5 ± 4.7) kJ · mol−1 in satisfactory agreement with two previous indirectly derived values.

The enthalpy of formation of 1,1,2-trifluoro-1,2,2-trichloroethane

Abstract The energy of combustion of 1,1,2-trifluoro-1,2,2-trichloroethane has been determined with the aid of two rotating-bomb calorimeters. The values of ΔHfo(C(CF2ClCFCl2), 1, 298.15 K) = −(745.0±4.3) kJ mol−1 and ΔHfo(CF2ClCFCl2, g, 298.15 K) = −(716.8 ± 4.3) kJ mol−1 were calculated. Using these values the enthalpy of formation of trifluorochloroethylene: ΔHfo(CF2 CFCl, g, 298.15 K) = −(512.0±4.7) kJ mol−1, has been obtained.

Thermodynamic properties of oxygen-containing organofluorine compounds Enthalpies of formation of dimethylperfluoroglutarate and perfluoro-di-n-amyl ether

Abstract Energies of combustion of dimethylperfluoroglutarate and perfluoro-di- n -amyl ether have been determined with a rotating-bomb calorimeter and enthalpies of formation at 298.15 K have been derived for the compounds in the liquid and gaseous states. The results are: dimethylperfluoroglutarate, ΔH f o (l) = −468.4 kcal th mol −1 and ΔH f o (g) = −455.9 kcal th mol −1 ; perfluoro-di- n -amyl ether, ΔH f o (l) = −1143.2 kcal th mol −1 and ΔH f o (g) = −1131.9 kcal th mol −1 . The influence of electrophilic group interactions on ΔH f o of oxygen-containing organofluorine compounds is discussed.

Enthalpy of formation of perfluoro-2,7-dimethyloctane

Abstract The energy of combustion of perfluoro-2,7-dimethyloctane has been measured in a rotating bomb calorimeter, Δ c U 0 (1) = −3198.2 ± 8.6 kJ mol −1 . The enthalpy of formation, Δ f H 0 (1) has been obtained by combination of the experimental data with the accepted values for the enthalpies of formation of water, carbon dioxide and aqueous hydrofluoric acid.

The energy of combustion of liquid 1,2-dichlorotetrafluoroethane

Abstract The energy of combustion at 298.15 K of liquid 1,2-dichlorotetrafluoroethane has been determined by rotating-bomb calorimetry. The standard enthalpy of formation derived from these measurements. Δ f H 0 (CF 2 ClCF 2 Cl(g), 298.15 K) = −(937.0±7.3) kJ mol −1 , is in satisfactory agreement with the value calculated previously using the energy of combustion of the gaseous compound.

The enthalpies of formation of 1,1,1-trifluoro-2-chloro-2-bromoethane and 1,1,2-trifluoro-2-chloro-1-bromoethane

The energies of combustion of two isomers of trifluorochlorobromoethane have been determined by rotating-bomb calorimetry. The values of the enthalpies of formation: ΔHfo(CF3CHClBr, g) = −(690.4 ± 4.9) kJ mol−1 and ΔHfo(CF2BrCHFCl, g) = −(644.8 ± 6.4) kJ mol−1 were derived. Using the latter value, the enthalpy of formation of trifluorochloroethylene CF2:CFCl was found to be −(500.0 ± 6.5) kJ mol−1.