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

Abstract

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 groupsubstituted bipyrazoles containing the largest number of nitro groups among the bisazole 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 °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.

Understanding the Stability of Highly Nitrated Sensitive Pyrazole Isomers

“…Nevertheless, the synthesis and development of highly nitrated compounds are very challenging because of their conflicting energy and safety characteristics. − Generally, the larger the number of nitro groups, the better the energetic performance. , However, the former also results in higher sensitivity and lower stability, making striking a balance between these critical parameters more difficult. − The aim of the current study is to address these challenges by examining isomerism in heavily nitrated pyrazoles . It is hypothesized that structural isomerism can be leveraged to create energetic compounds with enhanced stability and reduced sensitivity, while maintaining high energy density.…”

“…14−16 Generally, the larger the number of nitro groups, the better the energetic performance. 17,18 However, the former also results in higher sensitivity and lower stability, making striking a balance between these critical parameters more difficult. 19−23 The aim of the current study is to address these challenges by examining isomerism in heavily nitrated pyrazoles.…”