Study on the thermal decomposition of capecitabine

Abstract

The thermal decomposition of capecitabine (CAP) was measured with thermogravimetry, differential scanning calorimetry, and thermogravimetric analysis coupled with Fourier transform infrared spectroscopy. The IR spectra, high-performance liquid chromatography, and liquid chromatography–mass spectrometry of CAP and the residue of its thermal decomposition at various temperatures were determined. The molecular bond orders were calculated using an ab initio method from the GAMESS program of quantum chemistry. The mode of thermal decomposition for CAP was discussed. The kinetic parameters for thermal decomposition such as activation energy E a and the pre-exponential factor A were obtained using the Ozawa method. The prospective lifetime of CAP was estimated using the Dakin equation. The results indicated that the thermal decomposition of CAP is a three-step process, and the first mass loss stage is to lose pentyl formate. The initial decomposition temperature in either nitrogen or air is 120 °C. For decomposition in nitrogen, the E a and A for the initial thermal decomposition are 105.1 kJ mol−1 and 9.12 × 1011 min−1, respectively. For decomposition in air, the corresponding E a and A are 105.1 kJ mol−1 and 9.55 × 1011 min−1, respectively. The CAP has poor thermal stability under routine temperature.