Thermal analysis and powder X-ray diffraction study of terpin - Evidence of a eutectic 'hydrate/anhydrous form'

When the DSC analysis of different samples of terpin hydrate is carried out, a non identified small endotherm is observed at about 100 degrees C, just before the melting endotherm. This phenomenon is detected whatever the experimental conditions are. After some trials, this endotherm was identified as an eutectic formed with terpin hydrate and desolvated terpin (17/83). The importance of the experimental conditions is preponderant. In an open pan, the desolvation occurs and the melting endotherm of the anhydrous form can be observed at 105 degrees C. In a closed pan, no desolvation is detected and the melting endotherm at 120 degrees C is that of the terpin hydrate. The eutectic exhibits a good compression ability and a fast dissolution. Its stability is correct. Its use in therapeutic tablets can be envisaged. The eutectic structure could be, more generally, favourable to compression owing to the isotropic texture of this particular solid state.