Pushing the boundaries of the oxygen balance of a pyrazole ring

Highly nitrated azoles exhibit high densities and good oxygen balances, and they are potential oxidizing agents in solid propellants and space exploration, replacing environmentally hazardous materials, such as ammonium perchlorate. However, synthesizing such compounds is often very challenging because of the instability caused by multiple nitro groups and limited numbers of modification sites on their azole rings. In this study, two high-energy oxidizers, i.e., 3,5-dinitro-1,4-bis(trinitromethyl)-1H-pyrazole and 4,5-dinitro-1,3-bis(trinitromethyl)-1H-pyrazole, were synthesized using a three-phase nitration strategy. Notably, they are the first examples of single azole rings bonded to eight nitro groups. Both compounds exhibit exceptional physicochemical properties, with positive oxygen balances (21.1%) and good thermal stabilities (147.0 and 145.5 °C). This study represents a significant advancement in determining the limits of the oxygen balances of compounds based on single pyrazole rings, thus contributing to the exploration of highly nitrated compounds.