V.M. Sevruk

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.

Thermodynamic properties of cyclohexanone oxime

The heat capacity of crystalline and liquid cyclohexanone oxime was measured by vacuum adiabatic calorimetry (T = 6 K to 300 K) and by the triple heat bridge method (T = 300 K to 450 K). The melting temperature Tm = 362.5 K and molar enthalpy of fusion ΔfusHom = (12.7 ± 0.3) kJ·mol−1 were obtained by the latter method. The molar enthalpy of sublimation of cyclohexanone oxime: ΔsubHom(354 K) = (74.01 ± 0.33) kJ·mol−1 and the molar enthalpy of vaporization: ΔvapHom(367.8 K) = (58.66 ± 0.56) kJ·mol−1 were determined by a heat-conduction differential calorimeter of Calvet type. The saturated vapour pressure p of crystalline cyclohexanone oxime was measured by the integral effusion Knudsen method at temperatures from 287.9 K to 348.3 K. ln ( p / Pa ) = ( 33.307 ± 0.255 ) − ( 9607 ± 80 ) ⋅ ( K / T ) , and the molar enthalpy of sublimation was calculated: ΔsubHom(317.5 K) = (79.88 ± 0.67) kJ·mol−1. The saturated vapour pressure of liquid cyclohexanone oxime was determined by a static method using a membrane null-manometer at the temperatures 370.9 K to 446.3 K: ln ( p / Pa ) = ( 26.469 ± 0.130 ) − ( 7151 ± 55 ) ⋅ ( K / T ) and the molar enthalpy of vaporization was calculated: ΔvapHom(409.2 K) = (59.46 ± 0.46) kJ·mol−1. From these results the weight-average value of the molar enthalpy of sublimation: ΔsubHom(317.5 K) = (77.08 ± 0.30) kJ·mol−1, was calculated and the molar entropy of gaseous cyclohexanone oxime: Som(g, 320 K) (371.53 ± 1.03) J·K−1·mol−1, was found. The standard molar enthalpy of combustion of solid cyclohexanone oxime: ΔcHom(cr, 298.15 K) = −(153.20 ± 2.34) kJ·mol−1, was determined in the calorimeter with an isothermal jacket. The infrared absorption and Raman spectra of cyclohexanone oxime in the crystalline state were recorded and assignment of frequencies of normal vibrations in the molecule was carried out. As a result of statistical calculation the value of the standard molar entropy of gaseous cyclohexanone oxime is Som(g, 320 K) = 379.22 J·K−1·mol−1. Standard molar thermodynamic functions of cyclohexanone oxime in the condensed state (T = 0 to 450 K) and in the gaseous state (T = 100 K to 1000 K) were calculated and tabulated.

STANDARD ENTHALPIES OF FORMATION FOR SOME SEMI-PRODUCTS AT THE SYNTHESIS OF POLY(ETHYLENE) TEREPHTHALATE

The enthalpies of combustion for 4-formylbenzoic acid (I), 4-methylbenzyl alcohol (II), and trimethyl 1,2,4-benzenetricarboxylate (III) were determined by the bomb calorimetry method. Enthalpies of sublimation for I and II were measured with a calorimeter. The contributions of different substituents to the standard enthalpies of formation for benzene derivatives in the gas state were derived.