Thermal hazard and pyrolysis mechanism investigation using thermal analysis coupled with quantum-chemical DFT simulation for 1-hydroxy-7-azabenzotriazole

1-Hydroxy-7-azabenzotriazole (HOAT) as a key benzotriazole derivative has been widely used in biological, chemical, and pharmaceutical fields. Nevertheless, its energetic property was usually neglected and its thermal hazard characteristics were still unknown. Therefore, this study focused on analyzing the thermal hazard characteristics of HOAT in nonisothermal, isothermal, and adiabatic conditions through differential scanning calorimetry, thermogravimetric analyzer, and accelerating rate calorimeter. The relevant thermal decomposition parameters and process safety parameters were evaluated, and the most probable mechanistic function of the main exothermic stage of HOAT decomposition was identified. The microscopic pyrolysis mechanisms of HOAT were investigated based on density functional theory calculations, thermogravimetric-photoionization mass spectrometry, X-ray photoelectron spectroscopy, and energy-dispersive spectra tests. Electrostatic potentials, Laplacian bond order, and main decomposition pathways of HOAT pyrolysis were explored. The research results demonstrated that HOAT decomposition is a process with large amounts of heat and gas released rapidly. The main gaseous products include N₂, C₂H₂, NO, and HCN. The most dangerous step is the six-membered ring opening to form a five-membered carbon–nitrogen heterocyclic with higher heat release. This study contributed to understanding the thermal decomposition characteristics of HOAT and properly providing guidance for improving the thermal safety of HOAT production, transportation, storage, application and formulating emergency plans for related thermal hazards. Graphical abstract: [Figure not available: see fulltext.]