Reaction Mechanism and Thermal Hazard Analysis of 4,10-Dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane Synthesis Process

4,10-Dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane (TEX) synthesis process involves potential thermal hazards and ambiguous reaction mechanisms, which hinder safe and efficient production. This study systematically investigates the reaction mechanism and thermal hazards of the TEX synthesis process. The key intermediates, DFIW and its mononitro derivatives, were identified by HPLC-MS and FTIR. Quantitative analysis of their concentration profiles, together with that of TEX, supports a reaction mechanism involving precage formation followed by nitration, which was further verified by density functional theory (DFT) calculations. Furthermore, reaction calorimetry (RC1e) and differential scanning calorimetry (DSC) were used to evaluate the exothermic characteristics and thermal stability. RC1e results show that the heating rate significantly affects exothermic behavior: increasing the heating rate reduces both the total heat release (Q) and the maximum temperature of the synthesis reaction (MTSR), likely due to excessive volatilization of fuming acid during the reaction. DSC analysis indicates that fuming nitric acid catalyzes the thermal decomposition of TEX, thereby elevating the thermal hazard of the synthesis process. The temperature corresponding to the maximum reaction rate reached in 24 h under adiabatic conditions (TD24) for the final reaction solution is predicted to be 131.5 °C. Finally, risk assessment based on heating rate reveals distinct criticality classes: at higher heating rates (1.0 and 1.5 K·min–1), TD24 > MTSR, resulting in a criticality class of 3; in contrast, at 0.5 K·min–1, TD24 < MTSR raises the criticality class to 4, indicating a substantially increased thermal runaway risk. These findings underscore the necessity of protective measures and provide crucial guidance for the safe production of TEX.