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)-1 H ,1' H -4,4'-bipyrazole ( 3 ), was designed and synthesized. Compared to the isomer 4,4',5,5'-tetranitro-2,2'-bis(trinitromethyl)-2 H ,2' H -3,3'-bipyrazole ( 4 ) ( T d = 125 °C), 3 possesses better thermostability ( T d = 156 °C), which is close to that of ammonium dinitramide ( ADN ) ( T d = 159 °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.