Thermal, phase transition, and thermal kinetics studies of carbamazepine

Abstract

The thermal, phase transition of carbamazepine dihydrate and the solid-state transformation of carbamazepine from form III to form I were performed by Differential scanning calorimetry (DSC), Thermo gravimetry (TG-DTA), and X-ray powder diffraction.The non-thermal kinetic analysis of carbamazepine dihydrate and form III was carried out by DSC at different heating rates in dynamic nitrogen atmosphere. The model-free model, the Kissinger method, was used to give the Arrhenius parameters. Arrhenius plots from the kinetic model yielded activation energies corresponding to dehydration of dihydrate and melting of anhydrate CBZ form I were 95.28, 966.06 kJ mol -1 , the pre-exponential factors were 8.34E?11 and 1.41E?149, respectively. For the transformation of carbamazepine from form III to form I, activation energies corresponding to the melting of CBZ form III, recrystallization of form I, and melting of form I were 1160.81, 710.89, 1265.89 kJ mol -1 , the pre-exponential factors were 2.29E?144, 4.43E?91, and 1.61E?151, respectively. As a comparison, Ozawa method was used to verify the activation energy values obtained by Kissinger method. The result shows a close activation energy values between two methods.

Thermoanalytical studies of carbamazepine: hydration/dehydration, thermal decomposition, and solid phase transitions

“…The first endothermic peak, at 67.1 °C, was attributed to dehydration, and the second endothermic peak, at 147.8 °C, was attributed to melting of the anhydrous polymorphic Form III (Liu, Dang, Wei, 2012;Kobayashi et al, 2000). The exothermic peak at 174.4 °C and the sharp endothermic peak at 184.9 °C corresponded to crystallization and to melting of the polymorphic Form I, respectively.…”

“…The most stable known anhydrous form under room conditions is Form III. It is also known that in a humid environment, the anhydrates take up water and convert to the hydrates (Liu, Dang, Wei, 2012). Forms I and III of the drug constitute an enantiotropic pair, whose relative thermodynamic stability changes at 70 °C.…”

“…It is therefore important to investigate the stability and thermal behavior of the spontaneously hydrated form, the regeneration of the active anhydrous Form III, and the polymorphic conversions involved in this process. Thermal analyses employing DSC and TG-DTA have been used previously to gain insight into the thermal behaviors of hydrated CBZ and Form III (Liu, Dang, Wei, 2012;McGregor et al, 2004;Han, Suryanarayanan, 1997).Although Liu and co-workers (Liu, Dang, Wei, 2012) recently described the thermal behavior of hydrated carbamazepine, considering dehydration, degradation, and kinetic data, to the best of our knowledge there have been no detailed studies of the degradation of CBZ and the formation of volatile products using TG-FTIR and DSC with heat-cool-heat cycles in order to elucidate the crystallization processes.…”

Structure and Stability of Racemic and Enantiopure Pimobendan Monohydrates: On the Phenomenon of Unusually High Stability

“…The stability of hydrates in general is determined by the crystal structure − (if other factors including the sample itself and its preparation can be assumed to be of a minor importance) and depends on temperature and water activity it is exposed to. − However, dehydration as a process is affected by particle size and the crystallinity of the sample, as well as dehydration conditions, such as the heating rate, humidity, and inert gas flow rate. − Nevertheless, dehydration temperature, if determined for a well described system under well-defined conditions, is a meaningful parameter that can be used to compare the stability of hydrates (solvates). , Usually, by performing the dehydration of organic molecule hydrates upon heating, the onset temperature is below the boiling point of water. ,,− Because of strong ion–dipole interactions, higher dehydration temperatures are observed for ionic organic compounds, especially when a metal ion is present. , …”

Solvent-Mediated Polymorphic Transformation of Famoxadone from Form II to Form I in Several Mixed Solvent Systems

“…Taking all this into account, the nucleation and growth rate can be assumed to be constant. In order to compare SMPT rates quantitatively in different mixed solvent systems, experimental data were fitted with an appropriate kinetic model [30,31]. Solid-state kinetic models are theoretical, mathematical descriptions of experimental data and are usually expressed as rate equations [32].…”