Probing the Effects of Deuteration on the Structure and Thermal Behavior of TNT-d₅

TNT and TNT-d₅ were synthesized through a nitration process in nitrating mixtures. The molecular structure, deuterium isotopic content, and C−H(D) bonds vibrational properties of them were investigated by ¹H, ²H, and ¹³C NMR and FTIR. The results suggested that the methyl group of TNT-d₅ containing residual protons may have two ²H nuclei and one ¹H nucleus (−CD₂H). Furthermore, the deuteration of TNT resulted in an evident red-shift phenomenon with the ratio of the stretch frequencies ((Formula presented.)) is about 1.36. The effect of deuteration on the thermal decomposition of TNT is obtained in isothermal conditions. The isothermal decomposition of TNT and TNT-d₅ have obvious autocatalytic characters, and the Arrhenius constant of each reaction stage was obtained. For the non-catalytic and catalytic decomposition stages, TNT has significant deuterium isotope effects (k_{1, H}/k_{1, D}=1.49, k_{2, H}/k_{2, D}=1.39). Meanwhile, the non-isothermal decomposition kinetic parameters of TNT-d₅ and TNT were obtained using Kissinger's and Ozawa's methods. The values of apparent activation energy for TNT-d₅ (E_K=129.91 kJ/mol, E_O=133.12 kJ/mol) are higher than those for TNT (E_K=113.43 kJ/mol, E_O=117.21 kJ/mol), which implies the higher thermal stability of TNT-d₅. The calculated thermal explosion critical temperatures of TNT (T_b=564.54 K) and TNT-d₅ (T_b=578.02 K) also support this conclusion. Finally, the thermodynamic parameters of the non-isothermal decomposition process were also calculated and discussed.