Investigation on the decomposition kinetics, thermal safety and mechanism of the nitration products of m-xylene: experiment and DFT calculations

Background: Nitro-m-xylene (NMX) is a critical raw material and intermediate widely used in the synthesis of fine chemical products and energetic materials. A clear understanding of the thermal hazards and safety performance of NMX is especially critical for practical applications in chemical processes.

Methods: Calorimetric experiments combined with theoretical chemical calculations were applied to investigate the thermal decomposition and kinetic behavior of NMX.

Significant findings: The average apparent activation energies for the decomposition of NMX, the nitration products of m-xylene, calculated using the DAEM, Starink and Friedman methods were 141.1 kJ/mol, 141.4 kJ/mol and 144.9 kJ/mol, respectively. The most probable decomposition mechanism functions were determined by the master plots method at conversions of 0.05–0.50 and 0.50–0.95 for modes A4 and F2, separately. Furthermore, calculations of thermal safety and thermodynamic parameters revealed the excellent thermal stability of the nitration products, which require an external heat source to trigger decomposition. The C-NO₂ bond was identified as a possible initial decomposition site for 4-NMX by theoretical bond order and dual descriptor analysis. The possible decomposition pathways for 4-NMX were deduced by density functional theory, and alkyl compounds were the main gaseous products, followed by small molecules containing O and N.