Photolysis of the Insensitive Explosive 1,3,5-Triamino-2,4,6-trinitrobenzene (TATB).

Annamaria Halasz,Nancy N Perreault,Jalal Hawari

doi:10.3390/molecules27010214

Annamaria Halasz, Nancy N Perreault + Show 1 more

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https://doi.org/10.3390/molecules27010214

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Abstract

The explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is of particular interest due to its extreme insensitivity to impact, shock and heat, while providing a good detonation velocity. To determine its fate under environmental conditions, TATB powder was irradiated with simulated sunlight and, in water, under UV light at 254 nm. The hydrolysis of particles submerged in neutral and alkaline solutions was also examined. We found that, by changing experimental conditions (e.g., light source, and mass and physical state of TATB), the intermediates and final products were slightly different. Mono-benzofurazan was the major transformation product in both irradiation systems. Two minor transformation products, the aci-nitro form of TATB and 3,5-diamino-2,4,6-trinitrophenol, were detected under solar light, while 1,3,5-triamino-2-nitroso-4,6-dinitrobenzene, 1,3,5-triamino-2,4-dinitrobenzene and mono-benzofuroxan were produced under UV light. The product identified as 3,5-diamino-2,4,6-trinitrophenol was identical to the one formed in the dark under alkaline conditions (pH 13) and in water incubated at either 50 °C or aged at ambient conditions. Interestingly, when only a few milligrams of TATB were irradiated with simulated sunlight, the aci-isomer and mono-benzofurazan derivative were detected; however, the hydrolysis product 3,5-diamino-2,4,6-trinitrophenol formed only much later in the absence of light. This suggests that the water released from TATB to form mono-benzofurazan was trapped in the interstitial space between the TATB layers and slowly hydrolyzed the relatively stable aci-nitro intermediate to 3,5-diamino-2,4,6-trinitrophenol. This environmentally relevant discovery provides data on the fate of TATB in surface environments exposed to sunlight, which can transform the insoluble substrate into more soluble and corrosive derivatives, such as 3,5-diamino-2,4,6-trinitrophenol, and that some hydrolytic transformation can continue even without light.

Highlights

For several decades, 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) have been the most commonly used military explosives
The degradation products were analyzed by LC-MS using electrospray ionization in the negative mode (ESI-), producing mainly deprotonated molecular mass ions [M − H]−
The formation of the aci-nitro isomer of TATB requires a relatively low energy of 42.1 kcal/mol, subsequent cyclization by removing water to produce mono-benzofurazan requires an overall activating barrier of 68.6 kcal/mol [14], which is much higher than that calculated for the biradical process, 47.5 kcal/mol [15]; this suggests that the precursor of the monobenzofurazan derivative of TATB (C1) is rather a biradical during photolysis by simulated sunlight (Scheme 1, route 1)

Summary

Introduction

2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) have been the most commonly used military explosives. The environmental fate of insensitive EMs, such as TATB, and their products requires particular attention because some insensitive munition rounds are less efficient in highorder and blow-in-place detonations, depositing greater masses of energetic residues per round [3]. Attempts to identity the TATB green product have led to different assumptions, and the mechanism of color formation and transformation is still controversial. Williams et al [7] confirmed the formation of a free radical using electron paramagnetic resonance (EPR) spectroscopy of the green powder generated after UV-irradiation of TATB. The green color was attributed to the formation of the mono-nitroso derivative of TATB [6] or to a furazan derivative detected during gamma irradiation of TATB [9]. The color change of TATB was attributed to physical structural transformations instead [10]

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