A kinetics and mechanism study of the thermal decomposition of energetic materials

Jun Zhang, University of Rhode Island

Abstract

The thermal decomposition rates and product distributions have been studied for two groups of compounds: nitro- and difluoramino-substituted six-membered rings and 3,6-disubstituted-1,2,4,5-tetrazines. The mass spectra of these compounds were also examined using electron impact (EI) mass spectrometry (MS). A collision induced dissociation (CID) study of the major EI peaks was carried out using tandem mass spectrometer. The mass fragmentation pathways were constructed and discussed. ^ Geminal-bis(difluoramino) compounds were observed to be slightly more stable than the corresponding geminal dinitro compounds, and they released more heat during decomposition. Where a nitramine functionality was present, the nitroso analog was observed as a major decomposition product. The decomposition pathways of gem-bis(difluoramino) and gem-dinitro compounds exhibited similarities. Both experienced homolytic loss of one NX2 group followed by the rearrangement of the remaining NX2. Where X was oxygen, the well-known nitro/nitrite rearrangement, followed by loss of NO, resulted in a C=O bond. Where X was fluorine, there were two possibilities; loss of fluorine radical leaving C=NF or loss of HNF resulting in =C-F; the latter pathway was the one mainly observed. ^ The mass fragmentation study on these compounds indicated the two nitramines with a six-member ring structure underwent initial loss of a geminal substituent; loss of a nitramine nitro group was the secondary step. The two cyclohexane structures showed similar initial fragmentation pathways, featuring the successive losses of nitro or difluoramino groups. ^ The thermal and electron-impact stabilities of eight 3,6-substituted-1,2,4,5-tetrazines were investigated in the same fashion. Major EI peaks were also investigated by tandem mass techniques to construct fragmentation pathways. No tetrazine ring structures were maintained under electron impact ionization nor under conditions of thermal decomposition. Under electron impact, all the tetrazines examined shared the same initial fragmentation pathways: elimination of two of the nitrogen atoms as N2 from the tetrazine ring and cleavage of the remaining N-N bond. This pathway was also applicable to thermal decomposition; however, the main route involves dissociation of the substituent on the tetrazine carbon, in some cases assisted by proton transfer. ^

Subject Area

Chemistry, Analytical|Chemistry, Inorganic

Recommended Citation

Jun Zhang, "A kinetics and mechanism study of the thermal decomposition of energetic materials" (2000). Dissertations and Master's Theses (Campus Access). Paper AAI9988241.
http://digitalcommons.uri.edu/dissertations/AAI9988241

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