Thermal studies on the polymorphic modifications of (R,S) propranolol hydrochloride

Abstract

The polymorphism of (R,S) propranolol hydrochloride was investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray powder diffractometry (XRPD) and thermomicroscopy (HSM) coupled with FT-IR spectroscopy. Propranolol hydrochloride existed in three different crystalline forms, denoted as forms I, II and III, according to their decreasing melting temperatures. Modification II was the commercial product. The forms I and III were obtained by melting form II in different experimental conditions. Form III was obtained only by solidification of the melt in the presence of an alkali halide matrix (as a crystalline film on an alkali halide window or as powder dispersion in a KBr pellet). Forms I and II were also obtained by crystallization from 95% aqueous ethanol and acetone, respectively. The three forms were easily differentiated by their IR spectra in the 3400–2000 cm −1 range. The different crystalline structures of forms I and II were characterized by means of their X-ray powder diffraction patterns.