Adrenaline system: another rare case of conglomerate with partial solid solutions

Adrenaline, in its enantiomeric form l-, is the drug of choice for the treatment of cardiac arrest or certain serious shock conditions. However, although its crystal structure is known, there are no thermodynamic data on this molecule. Regarding the racemic form of this molecule, the latter has never been characterized either from a thermodynamic or crystallographic point of view. The melting characteristics, temperature and enthalpy of both the enantiomer and the racemate of adrenaline were determined using the plateau values obtained at high DSC scan rates. The refinement of the RX diffraction pattern of the racemate revealed that this equimolar mixture was a conglomerate with partial solid solutions. This conclusion was supported by the phase diagram between the two enantiomers established from the l-enantiomer and the racemate where the results presented in this paper show that a lower solid-state miscibility exists between the two enantiomers. The equimolar compound is therefore part of the very limited series of conglomerate with partial miscibility.