Backbone Isomerization to Enhance Thermal Stability and Decrease Mechanical Sensitivities of 10 Nitro-Substituted Bipyrazoles

The development of novel, environmentally friendly, and high-energy oxidizers remains interesting and challenging for replacing halogen-containing ammonium perchloride (AP). The trinitromethyl moiety is one of the most promising substituents for designing high-energy density oxidizers. In this study, a backbone isomerization strategy was utilized to manipulate the properties of 10 nitro group-substituted bipyrazoles containing the largest number of nitro groups among the bis-azole backbones so far. Another advanced high-energy density oxidizer, 3,3 ',5,5 '-tetranitro-1,1 '-bis(trinitromethyl)-1H,1 ' H-4,4 '-bipyrazole (3), was designed and synthesized. Compared to the isomer 4,4 ',5,5 '-tetranitro-2,2 '-bis(trinitromethyl)-2H,2 ' H-3,3 '-bipyrazole (4) (T-d = 125 degrees C), 3 possesses better thermostability (T-d = 156 degrees C), which is close to that of ammonium dinitramide (ADN) (T-d = 159 degrees C), and it possesses better mechanical sensitivity (impact sensitivity (IS) = 13 J and friction sensitivity (FS) = 240 N) than that of 4 (IS = 9 J and FS = 215 N), thereby demonstrating a promising perspective for practical applications.