Solid-Liquid Equilibrium of Tröger's Base Enantiomers in Ethanol: Experiments and Modelling

Thermodynamic properties of the enantiomers of the Tröger's base as crystals and in ethanol solutions have been studied by means of a suite of analytical techniques. We report the melting diagrams of the two enantiomers, providing evidence for the formation of a solid racemic compound. We present also ternary equilibrium data about the solubility of the two enantiomers in ethanol at 25°, 35°, and 50°. The melting‐diagram data are described well by the SchroederVan Laar and PrigogineVieland equations, when the melting temperatures and enthalpies of pure enantiomer and of the racemic compound are provided and with the assumption that the melting behavior is ideal. The ternary equilibrium data were well‐described when nonideality of mixtures of ethanol and the enantiomers is accounted for in terms of the non‐random two liquids (NRTL) model. Finally, we present the newly determined X‐ray crystal structure of an orthorhombic form of the pure Tröger's base (+)‐enantiomer.