THERMODYNAMIC PROPERTIES OF 6-AMINOHEXANOIC LACTAM (EPSILON-CAPROLACTAM)

The heat capacities of crystalline and liquid e{open}-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 e{open}-caprolactam was directly determined by a heat-conduction differential calorimeter: ΔsubHom(338 K) = (86.30±0.22) kJ · mol-1. The saturated vapour pressure of solid e{open}-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 ΔsubHom(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 e{open}-caprolactam: Som(g, 320 K) = (377.0±2.6) J · K-1 · mol-1 and Som(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 e{open}-caprolactam: ΔcHom(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 e{open}-caprolactam were made. Statistical calculation of the thermodynamic properties of e{open}-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: Som(g, 320 K) = 374.25 J · K-1 · mol-1 is in satisfactory agreement with the experimental values. Thermodynamic properties of e{open}-caprolactam in the condensed state (0 to 550 K) and in the ideal-gas state (100 K to 1000 K) were calculated and tabulated. © 1992 Academic Press Limited All rights reserved.