Thermal decomposition mechanisms of nitro-1,2,4-triazoles: A theoretical study

Abstract

Possible decomposition mechanisms of C nitro and N nitro 1,2,4 triazoles were simu lated. We showed that in addition to the experimentally detected thermolysis products includ ing N 2 , N 2 O, NO, CO 2 , HCN, HNCO, 1,2,4 triazole, 3(5) nitroso 1,2,4 triazole, and 1,2,4 triazolone, some other decompositon products (H 2 O, CO, NO 2 , cyanamide, cyanuric acid, and melamine) can be formed. Using the density functional approach (B3LYP/6 31G* approximation), we assessed the most favorable thermal decomposition pathways of nitro triazoles and studied the relationships between the thermolysis pathways of these substances and their molecular and electronic structures. We found a correlation between the energy gap width (energy difference between the frontier molecular orbitals) and the stabilities of the C nitro 1,2,4 triazole tautomers to thermal decomposition.

Thermochemistry and Initial Decomposition Pathways of Triazole Energetic Materials

“…The Gibbs free energy of P15 is 69.8 kcal/mol, also too high to make the OH path be the primary decomposition path. The energy barrier of the OH elimination path is comparable to the previous work by Korolev et al, 37 in which the energy barrier is about 70 kcal/mol. The consistent energy barriers again prove the validity of the current work.…”

“…4,32−36 Nevertheless, less efforts have been made regarding triazole, leaving the thermolysis mechanism of triazole poorly understood. Korolev et al 37 investigated the thermal decomposition mechanism of nitro-1,2,4-triazole using density functional theory (DFT) and found the energy barriers of NO 2 elimination and nitro-nitrite rearrangement channels were about 67 and 65 kcal/mol, respectively. Removal of the hydroxyl radical (energy barrier: ∼50 kcal/mol) was found to be a preferable decomposition channel for the aci-nitro form tautomer of nitro-1,2,4-triazole (tautomerization energy: ∼23 kcal/mol).…”

Decomposition Mechanisms and Kinetics of Novel Energetic Molecules BNFF-1 and ANFF-1: Quantum-Chemical Modeling

“…The similar rearrangement in nitroethylene was found to require about 57.9 kcal/mol [58]. Close barriers were also obtained in C-nitro isomers of triazole (60.1–65.2, 63.5 kcal/mol [48]) and nitroaromatics, nitrobenzene (61.1 kcal/mol [59], 63.7 kcal/mol [60]) and trinitrotoluene (54.9 kcal/mol [61]). The BNFF-1 and ANFF-1’s behavior (Table 1) resembles the nitroethylene’s decomposition trend (with CONO-isomerization requiring ~15 kcal/mol less than the energy needed to cleave the C–NO 2 bond) [58] and somewhat differs from that of DADNE, which exhibits nearly isoenergetic reactions of the nitro-nitrite isomerization and the C-NO 2 cleavage [52].…”

“…Experimental and theoretical data on BNFF-1 and ANFF-1 are limited at the time being, therefore we will link our results to existing relevant literature on other nitro-compounds and general trends reported in earlier studies [44,45,46]. The calculated activation energies of the C–NO 2 homolysis of ANFF-1, 59.5–61.1 kcal/mol, and BNFF-1, 57.6–63.1 kcal/mol, rest at the lower end of the range of the typical dissociation energies of C–NO 2 bonds, 61–70 kcal/mol, determined for nitrofurazan (56.8 kcal/mol [47]), C-nitro derivatives of triazole (~67 kcal/mol [48]), a wide variety of nitroaromatics [44], including TATB (59–64 kcal/mol [45,49], ~70 kcal/mol [50,51]), DADNE (58–67.0 kcal/mol [52], ~70 kcal/mol [53]), and a series of related aminotrinitrobenzene compounds [45,46].…”

Time-resolved, laser initiated detonation of TATP supports the previously predicted non-redox mechanism

“…16 The calculated multistep decomposition pathway of 1, which predicted highly reactive intermediates, including various diradicals and singlet molecular oxygen, seemed counterintuitive on grounds of the commonly known redox processes of energetic materials. 20,21 Furthermore, the experimental observation of a fireball associated with the explosion of 1 seemed to disagree with the theoretical study, suggesting that 1, like all other energetic materials, decomposes via internal combustion processes. 22 Product analysis could provide an experimental support for these theoretical predictions.…”