Thermodynamics of mixtures containing amines: XIII. Application of the ERAS model to cyclic amine + alkane mixtures

Abstract

Primary or secondary cyclic amine+alkane mixtures have been investigated in the framework of the ERAS (Extended Real Associated Solution) model. The corresponding ERAS parameters are reported. All the amines considered have the same equilibrium constant (KA=0.75). Cyclopropylamine, cyclopentylamine, cyclohexylamine and pyrrolidine are characterized by the same enthalpy of self-association (ΔhA*=−15 kJ mol−1). Piperidine and hexamethyleneimine show a less negative ΔhA* value (−13kJmol−1). Experimental data on excess enthalpies, HmE, volumes, VmE, and isobaric heat capacities, CpmE, reveal the existence of physical interactions and structural effects in the studied solutions. The latter lead to values of self-association of pure amines, ΔvA*, which may depend on the solvent in systems with a given amine. Although the model overestimates the ΔhA* values, the relatively high values of the physical parameters XAB remark the importance of physical interactions. ERAS describes correctly the excess functions HmE, VmE, CpmE and GmE (molar Gibbs energy), and the enthalpy of vaporization of pure amines. Nevertheless, discrepancies with experimental data are found for the concentration dependence of VmE and GmE of some mixtures including cyclic primary amines.