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) {dot operator} (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) {dot operator} (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. © 1992 Academic Press Limited All rights reserved.