Thermodynamics of ketone + amine mixtures. Part X. Excess molar enthalpies at 298.15 K for N,N,N-triethylamine + 2-alkanone systems. Characterization of tertiary amine + 2-alkanone, and of amino-ketone + n-alkane mixtures in terms of DISQUAC

Abstract

Molar excess enthalpies, HmE, at 298.15K and 0.1MPa have been measured using a Tian–Calvet microcalorimeter for N,N,N-triethylamine (TEA)+2-alkanone mixtures. These data have been used to determine ΔHN-CO, the enthalpy of the amine-ketone interaction, which is practically independent of the ketone size. This allows explain the observed HmE decrease when the ketone size is increased in terms of a lower positive contribution to HmE from the breaking of the alkanone-alkanone interactions. Inspection of molar excess volumes and of molar excess internal energies at constant volume (determined in this work) reveals the existence of structural effects, which are more important for mixtures with 2-heptanone. Tertiary alkyl amine+2-alkanone, and amino-ketone+n-alkane mixtures have been treated in terms of DISQUAC. The interaction parameters for the carbonyl/amine contacts are reported. It is shown that such contacts are essentially dispersive. Proximity effects in amino-ketone mixtures lead to increased dispersive parameters in comparison to those of amine+ketone solutions. Steric effects related to the length of the alkyl chains attached to the N atom lead to decreased dispersive parameters. DISQUAC describes accurately vapour–liquid equilibria (VLE) and HmE of the investigated mixtures, which have been also treated using UNIFAC (Dortmund version). UNIFAC predictions compare well with DISQUAC results for TEA mixtures. For amino-ketone systems, UNIFAC calculations largely differ from the experimental results. This reveals that interactions parameters must be modified to take into account proximity effects.