Extensive Evaluation of Dinitropyrazole and Tetrazole-Based Energetic Compounds: Role of Isomerism and Oxygen Balance on the Overall Performance

Abstract

Nitrogen-rich heterocycles have been instrumental in the pursuit of design, synthesis, and modification of advanced energetic materials developed to fulfill evolving requirements. Thus, the role of material chemists is to bridge the research gap by understanding how different rings and functional groups influence overall performance. In this work, 3,4-dinitritropyrazole (3,4-DNP) and 3,5-dinitropyrazole (3,5-DNP) were taken as precursors for the synthesis of energetic materials having harmonized energy and safety. Utilizing N-methylene-C bridging, they were paired with tetrazole and N-hydroxytetrazole explosophores, followed by salt formation for performance modification. The isomeric dinitropyrazoles were found to be more favorable for pairing with the N-hydroxytetrazole than commonly utilized 4-substituted 3,5-dinitropyrazoles. Consequently, this marks the first report of an asymmetric combination involving the N-hydroxytetrazole moiety, achieved through the bridging approach. After the performance evaluation, a comparative assessment of isomeric analogues was implemented. The presence of an additional oxygen supplement results in higher energetic properties with respect to tetrazole-based compounds. All compounds demonstrated energetic performance superior to TNT and good physical stability. This study revealed that among the isomeric 3,4-DNP and 3,5-DNP derivatives, the energetic performance of neutral 3,4-DNP derivatives (7 and 15) was higher, and the thermal stability of the 3,5-DNP derivatives (8 and 16) was superior.