The nitration pattern of energetic 3,6-diamino-1,2,4,5-tetrazine derivatives containing azole functional groups

Abstract

One of the successful strategies for the design of promising new energetic materials is the incorporation of both fuel and oxidizer moieties into the same molecule. Therefore, during recent years, synthesis of various nitro-azole derivatives, as compounds with a more balanced oxygen content, has become very popular. In the framework of this effort, we studied nitration of N³,N⁶-bis(1H-tetrazol-5-yl)-1,2,4,5-tetrazine-3,6-diamine (BTATz; 5) and its alkylated derivative N³,N⁶-bis(2-methyl-2H-tetrazol-5-yl)-1,2,4,5-tetrazine-3,6-diamine 12, using a ¹⁵N-labeled nitration agent and monitoring and analyzing products of these reactions by ¹⁵N NMR. It was seen that the nitration of both compounds takes place only on the exocyclic (“bridging”) secondary amine groups. Possible tetranitro derivative isomers N,N′-(1,2,4,5-tetrazine-3,6-diyl)bis(N-(1-nitro-1H-tetrazol-5-yl)-nitramide) 6 and N,N′-(1,2,4,5-tetrazine-3,6-diyl)bis(N-(2-nitro-2H-tetrazol-5-yl)nitramide) 7, both of which have OB = 0% and calculated VODs of 9790 and 9903 m s⁻¹, respectively, could not be observed in the reaction mixtures, during the in situ¹⁵N NMR monitoring of nitration of 5, using ¹⁵N-labeled nitrating agents. Following a similar strategy, a new analog of BTATz – N³,N⁶-Bis(1H-1,2,4-triazol-5-yl)-1,2,4,5-tetrazine-3,6-diamine 15 was obtained and its nitration was studied. The reaction of 15 with a HNO₃–Ac₂O nitration mixture resulted in the formation of a new N³,N⁶-bis(3-nitro-1H-1,2,4-triazol-5-yl)-1,2,4,5-tetrazine-3,6-diamine derivative 20 in a moderate yield. Structures and properties of 15 (in the form of its perchlorate salt, 16) and 20 were measured by FTIR, multinuclear NMR, MS, DSC and X-ray crystallography. It is important to note that compound 20 exhibits exothermic decomposition at 302 °C (DSC) and >353 N (sensitivity to friction), making it a highly-promising thermally-insensitive energetic material for further development.