Studies on the Characteristics of Carbochromen Hydrochloride Crystals. I. Polymorphism and Behavior of Water of Crystallization

Abstract

To clarify the cause of cracking of carbochromen hydrochloride tablets on exposure to moisture, crystal modifications of the drug were investigated in detail. At least two hydrate forms (I and II) and three anhydrate forms (I', II' and III) were found. Analyses of X-ray powder diffraction patterns, infrared spectra, the activation energy of dehydration, and other data showed that water of crystallization contained in forms I and II has different roles in the crystals. Transformation from form I to form I' or vice versa produced a mosaic structure of the crystals, whereas mutual transformation between form II and form II' did not affect the appearance of the crystal, only causing contraction or expansion of the crystal in a certain direction. These differences are believed to be closely related to phenomena occurring in tablets prepared from these crystal forms.