Thermal hazard and pyrolysis mechanism of tetrazolo[1,5-a]pyridine by TG, DSC, ARC, TG-MS and DFT methods

The pyrolysis characteristics of tetrazolo[1,5-a]pyridine were investigated by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). The apparent activation energy (E_α) was estimated with DSC and various kinetic analysis methods, and it was determined that the decomposition of tetrazolo[1,5-a]pyridine follows the Avarami-Erofeve (A₂) reaction pattern. The thermal safety and thermodynamic parameters were calculated. In addition, the thermal runaway behavior and kinetic parameters under adiabatic conditions were studied by employing an adiabatic accelerating calorimeter (ARC). Thermogravimetric-photoionization mass spectrometry (TG-MS) was used to identify the vapor phase products of the pyrolysis process. The different decomposition pathways were analyzed by density functional theory (DFT). The main decomposition products were N₂, C₂H₂ and HCN according to TG-MS experiments and theoretical calculations. The most likely proposed decomposition mechanism proceeded through the opening of the tetrazole ring to dissociate N₂ and the rupturing of the pyridine ring to release C₂H₂ and HCN. The findings of these experiments and theoretical calculations can contribute to the determination of safety precautions for possible heat hazard accidents during the handling, transportation, use and storage of tetrazolo[1,5-a]pyridine.