Real-time measurements of the product gases arising from the thermal decomposition of triamino-trinitro benzene (TATB), its deuterated analogue, and plastically bonded TATB (LX-17) are presented in this study. Gas-phase decomposition products are identified by IR absorption spectroscopy. The frequency shifts in rovibrational spectra due to isotopic substitution and the change in rate of formation of decomposition products due to the kinetic-isotope-effect (KIE) help elucidate the decomposition pathways. The formation of H 2 O precedes other molecules (e. g., HCN, HNCO) during decomposition. After the concentrations of HCN and HNCO molecules reach a peak, their amounts gradually decrease. The concentrations of the other decomposition products (e. g., NH 3 and CO 2 ) rapidly rise after an induction period, which is attributed to the presence of autocatalytic reactions. The trends of chemical evo-lution are similar for all the samples, but their kinetic behaviors are different. This indicates the rates of consistent pathways are changed during thermal decomposition. The kinetics of deuterated TATB decomposition is slower than that of unsubstituted TATB due to the KIE (k H /k D~1 .41). The rate of LX-17 decomposition is slightly lower than unsubstituted TATB (k TATB /k LX-17~1 .15). The KIE is more pronounced during the early stage of decomposition, which is attributed to the first steps of TATB decomposition involving water formation (i. e., H vs D transfer). The KIE slows down the formation of all gases, including those lacking hydrogen (e. g., CO 2 ). These results suggest the TATB thermal decomposition mechanism might involve a series of pathways rather than a set of independent and parallel reactions.
Concerns surround whether insensitive (or any) energetic materials are more dangerous to handle when exposed to abnormal thermal environments. This study characterizes the residual material remaining after LX‐17 (92.5 % 1,3,5‐triamino 2,4,6‐trinitro benzene (TATB) and 7.5 % Kel‐F) is exposed to various thermal environments in a sealed small‐scale vessel cook‐off test reactor (heated at 0.1 to 100 °C/min until the reactor opened at 3000 psi (20.7 MPa)). Previous work has shown no additional sensitivity of these residues as evaluated by small‐scale safety analysis, but characterization on the molecular scale indicates the TATB is transformed to more reactive compounds as well as the residue could be precursors to toxic gases. The solids and chars were characterized by various analytical methods. Heat‐flow measurements indicated exothermic release is due to a mixture of residual TATB and related decomposition products (which may be more energetic). The N/C and O/N ratios indicated a material much more degraded than TATB. Primarily, the solids were a network of amorphous C inter‐dispersed with N and O. Types of bonding include C−C, C−N, N−H, N−C, N=C, N≡C, C−O=, and −OH. Solvent extracts of the solids showed TATB decomposition intermediates benzo‐furazans and benzo‐furoxans, substituted TATB (mono‐nitroso, hydroxyl, and chlorinated) along with several unidentified smaller molecules. These results indicate thermal treatment produces an amorphous carbon residue with heteroatoms incorporated through differing functionality, varying depending upon the thermal severity of exposure. These structures also could further decompose producing toxic light gases (such as cyanide).
Examining isotopically 15N-labeled versions of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) by NMR has experimentally demonstrated the effects of strong intra- and intermolecular hydrogen bonding on the solid-state and solution phase structure. Two isotopically labeled TATB compounds were synthesized using the wet-amination procedure: one with only the amino-nitrogen sites labeled, (15NH2)3-TATB, and the other with both the amino- and nitro-nitrogen sites labeled, (15NH2)3(15NO2)3-TATB. Isotopic and chemical purity was established by HPLC coupled to optical and mass spectroscopic detection. Solid-state NMR techniques (cross-polarization magic angle spinning (CP/MAS), 15N{1H} frequency switched, heteronuclear correlation (FSLG-HetCor)) were applied to assess the labeled nitrogen environments and revealed two distinctive nitrogen sites: one for the amino and one for the nitro. Closer examination of both sites revealed the nitro-nitrogen site represented one environment while the amino-nitrogen site represented three different environments. Equivalent solution NMR spectra show the presence of stable TATB tautomers in slow exchange with one another. A model was constructed (DFT to compute chemical shifts using the Gaussian16 revision A.03 computational code) demonstrating the inequivalence of the amino-nitrogen sites and shows essentially the equivalence of the nitro-nitrogen sites in the solid state. This provides further experimental evidence of intermolecular hydrogen bonding playing a significant role in the solid-state structure of TATB and possibly clarifies evidence of structural inequivalence suggested by some spectroscopic and crystallographic examinations. These results also may impact structure variations in future modeling studies.
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