Thermodynamic study of heptane + secondary, tertiary and cyclic amines mixtures. Part IV. Excess and solvation enthalpies at 298.15 K

Partial molar enthalpies and excess enthalpies HE of binary mixtures of heptane + secondary and tertiary n-alkyl, primary cycloalkyl, and secondary (hetero)cyclic amines have been determined at 298.15 K by isothermal titration calorimetry in the whole composition range. All mixtures showed positive HE values which decrease with increasing amine size in each category, and decrease in the order cyclic primary > cyclic secondary > linear primary [1] > secondary > tertiary when comparing amines of similar size in different categories. From partial molar enthalpies at infinite dilution and known enthalpies of vaporization, the solvation enthalpies have been calculated either for heptane in amines and for amines in heptane. These quantities, together with their cavitational and interactional terms obtained applying the scaled particle theory, are discussed to get insight into the types and relative strength of solute–solvent interactions and into their effects on molecular structure features such as branching and cyclization.

► Excess enthalpies of mixtures heptane + secondary and tertiary amine are positive.
► Enthalpies of solvation of amines in heptane and heptane in amines are strongly negative.
► Enthalpies of solvation are split into cavity and interaction contributions.
► Solute–solvent interactions of cyclic amines are stronger than those of open chain amines.
► Cyclization contribution to interaction decreases with increasing molecular size.