The thermodynamic properties of 2-methylaniline and trans-(R,S)-decahydroquinoline

Abstract

Measurements leading to the calculation of the ideal-gas thermodynamic properties for 2-methylaniline (Chemical Abstract registry number [95-53-4]) and trans-(R,S)-decahydroquinoline (registry number [767-92-0]) are reported. Experimental methods included combustion calorimetry, adiabatic heat-capacity calorimetry, vibrating-tube densitometry, comparative ebulliometry, inclined-piston gauge manometry, and differential-scanning calorimetry (d.s.c.). Standard molar entropies, enthalpies, and Gibbs free energies of formation were derived for the ideal gas at selected temperatures for both compounds. The critical temperature was determined for 2-methylaniline with the d.s.c. and the critical pressure and density were derived. Measured enthalpies of combustion, densities, vapor pressures, critical properties, and standard ideal-gas thermodynamic functions at p = p o = 101.325 kPa were compared with estimated and experimentally determined literature values. The experimental results were used to estimate magnitudes of methyl-group and amino-group rotation barriers in 2-methylaniline. The barriers are shown to be much larger than had been assumed in literature statistical thermodynamic-property evaluations.