The thermal decomposition mechanism and kinetics of tenoxicam

Tenoxicam (TNX) is a non-steroidal anti-inflammatory drug. Its thermal decomposition processes were studied with thermogravimetry and differential thermal analysis. The produced gaseous products and residues during decomposition were detected and characterized using Fourier transform infrared spectroscopy. Combining with the molecular bond order distribution obtained from the quantum chemistry calculation, the thermal decomposition mechanism of TNX has been speculated. The kinetic parameters for thermal decomposition, such as activation energy Eα and the pre-exponential factor A, were obtained using the ATSM E1641 method. The prospective lifetime of TNX was estimated using the ATSM E1877 method. The results indicated that the thermal decomposition of TNX is a three-stage process. During the first stage of thermal decomposition, the main part of the molecule, including sulfamide, thiophene and amide, decompose simultaneously, and to form gasifiable small molecules and carbonized residues. The initial decomposition temperature in either nitrogen or air is about 204°C. For decomposition in nitrogen, the Eα and A for the initial thermal decomposition are 174.8 kJ mol−1 and 2.512 × 1017  min−1, respectively. For decomposition in air, the corresponding Eα and A are 179.4 kJ mol−1 and 7.943 × 1017  min−1, respectively. The TNX has good thermal stability under routine temperature.