Polymorphism of mixtures of enantiomers: A thermodynamic study of mixtures of D- and L-limonene

The solid–liquid phase behaviour of the system {(1-x) mol L-limonene + x mol D-limonene} has been studied by means of adiabatic calorimetry. The system is polymorphic and the thermodynamic behaviour of mixtures of D- and L-limonene during temperature cycles has been investigated. The thermodynamic behaviour can be looked upon as the superposition of two phase diagrams. One phase diagram depicts the equilibrium between liquid and stable solid, and the other the equilibrium between liquid and metastable solid. The stable case corresponds to the formation of a racemic compound. The metastable case corresponds to a series of mixed crystals.