A potential insensitive-highly-energetic material through conjugation-promoted N-oxidation strategy

Striking a well balance between energy, sensitivity and thermostability of high performing organic materials has become a big challenge in the community of energetic materials. In the recent years, simple N-oxidation approach based on nitropyrimidine and nitropyridazine has been disclosed since the year of 1995 when nitropyrazine-N-oxides (such as LLM-105:2,6-diamino-3,5-dinitropyrazine-1-oxide) was developed, however, the development of facile N-oxidation via fused heterocylic ring is still stagnant, which has strongly limited the appearance of advanced materials. Herein, we present the specific synthesis of novel energetic materials with excellent properties in different aspects based on pyrazolium[5,1-C][1,2,4]triazine framework. Especially, for the first time we synthesized pyrazolium[5,1-C][1,2,4]triazine N-oxide, which also suggests that N-oxidation has introduced more intramolecular hydrogen bonds and resulted in larger conjugation effect at the molecular level, giving rise to an effective strategy in improving energy, safety and thermostability of energetic materials simultaneously. All compounds exhibit high densities (1.872–1.917 g·cm−3) and energetic performance (8657–8990 m·s−1). Among them, 8-nitro-3-(1H-tetrazol-5-yl)pyrazolo[5,1-c]00triazine-4,7-diamine (FPT-3) and 4-amino-7,8-dinitro-3-(1H-tetrazol-5-yl)pyrazolo[5,1-c][1,2,4]triazine-2-oxide (FPT-4) hold brilliant onset decomposition temperatures (FPT-3: Td = 335 °C; FPT-4: Td = 273 °C), good detonation properties (FPT-3: Vd = 8657 m s−1; FPT-4: Vd = 8851 m·s−1) and very low sensitivities (FPT-3: IS > 60 J, FS > 360 N; FPT-4: IS > 55 J, FS > 360 N), which indicate that both compounds are high energy explosives with very low sensitivity and excellent thermostability.