Theoretical study of the unimolecular decomposition mechanisms of energetic TNAD and TNAZ explosives

Abstract

Calculation methods based on hybrid Density Functional Theory (DFT)with the basis sets of the B3LYP/6-31ϩG(d)//B3LYP/4-31G(d) method and the differential overlap (INDO) program were used to derive reasonable decomposition mechanisms of 1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin (TNAD) and 1,3,3-trinitroazetidine (TNAZ) explosives. All possible decomposition species and transition states, including intermediates and products, were identified and their corresponding enthalpy of formation and Gibbs free energy of formation were obtained using polyparametric modification equations. INDO bond energy calculation results reveal the weakest bonding site for reference and determine where cleavage can occur easily. This work is concerned mainly with eliminating HONO (cis or trans form). The activation energy for trans-form HONO elimination is lower than that of cis-form HONO elimination in the initial steps of both TNAD and TNAZ decomposition, being 18.5 kJ/ mol and 33.3 kJ/mol, respectively.

Thermal decomposition of 1,3,3-trinitroazetidine (TNAZ): A density functional theory andab initiostudy

“…Liu et al 19 reported a concerted one-step barrier for cis-HONO elimination that is higher in energy than trans-HONO elimination (see Figures 2(a) and 2(b) of Ref. 19). Also, to our knowledge, cis-HONO elimination has not been included in any proposed HONO elimination mechanisms.…”

“…We unsuccessfully searched for a saddle point for cis-HONO elimination. Liu et al 19 reported a concerted one-step barrier for cis-HONO elimination that is higher in energy than trans-HONO elimination (see Figures 2(a) and 2(b) of Ref. 19).…”

“…Note that Alavi et al 18 and all others mentioned here who have studied HONO elimination theoretically only explored the trans-HONO elimination channel. Liu et al 19 predicted that NO 2 elimination by N-N initial bond fission requires 38.95 kcal/mol, while NO 2 elimination by C-N bond fission requires 55.24 kcal/mol. They only reported results for HONO elimination involving N-N bond fission; consequently, they reported that the energy barrier is 32.60 kcal/mol for trans-HONO elimination, while that for cis-HONO elimination is 40.05 kcal/mol.…”

“…They reported energy barriers of 45.00 kcal/mol and 44.00 kcal/mol for HONO elimination involving, respectively, the nitramine and nitroalkyl NO 2 . Liu et al 19 used B3LYP/6-31+G(d)//B3LYP/4-31G(d) and the Intermediate Neglect of Differential Overlap (INDO) semi-empirical method to investigate the cis-and trans-HONO eliminations channels. These channels are essentially the same except that the HONO product can adopt either a cis conformation or a trans conformation.…”

Computational study of FOX‐7 synthesis in a solvated reaction system

“…Theoretical kinetics study is very important and necessary to gain an understanding of the mechanisms of a specific reaction. Early computational work to explore reasonable decomposition pathways of energetic materials has been executed in our laboratory [11][12][13][14], with the aim that unexpected and intricate problems can be avoided while the experimental process is proceeding. This study is based on theory and refers to the kinetics of some energetic materials [15,16] to elucidate comparative reaction routes for FOX-7 synthesis.…”