Investigation of thermal degradation products of mebendazole by thermal and spectroscopic analysis

In this work, the thermal decomposition of mebendazole (MBZ) was studied to elucidate divergent data found in the literature concerning the thermal behavior of this drug. To this end, thermogravimetry-differential scanning calorimetry (TG-DSC), differential scanning calorimetry (DSC), evolved gas analysis (EGA), and DSC-photovisual analysis were employed to fully evaluate the polymorphic form A of MBZ. Our results showed that mebendazole undergoes mass loss starting at 205 °C with the release of methanol and carbon monoxide. Characterization of the main thermal decomposition product of MBZ through mid-infrared spectroscopy (MIR), proton nuclear magnetic resonance ( 1 H NMR), high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), and powder X-ray diffraction (PXRD) indicated the formation of 2-amino-5-benzoylbenzimidazole (MBZ-A). Kinetic parameters for MBZ and MBZ-A were also evaluated and shown herein.