The physicochemical characterization of the solid-state enantiomers and racemate of efaroxan hydrochloride (C13H17N2O+Cl-,
M=252.5 g mol-1) was performed by thermoanalytical methods (differential scanning calorimetry, thermogravimetry and thermomicroscopy)
and spectral methods (infrared spectrometry and X-ray diffractometry).
The efaroxan enantiomers and racemate were shown to be unstable near the melting point. At the beginning of the decomposition,
a loss of hydrogen chloride was observed. However when sealed pans were used, the compounds decomposed at higher temperature,
allowing a precise evaluation of the melting enthalpies by means of differential scanning calorimetry. The nature of the racemate
and its thermal stability were assessed by evaluating its free formation enthalpy. An enantiotropic solid-solid transformation
(II→I) was noted for the racemate; the reverse process (I→II) follows zero-order kinetics.