Thermal and combustion behavior of novel oxygen-rich energetic pyrazoles

Physicochemical properties, such as thermal decomposition, burning behavior, and flame structure of low-melting oxygen-rich energetic N-trinitromethyl-3,4-dinitropyrazole (1), N-trinitromethyl-3,5-dinitropyrazole (2), N-flurodinitromethyl-3,5-dinitropyrazole (3), and N-[(difluoroamino)dinitromethyl]-3,5-dinitropyrazole (4), have been studied. It has been found that the stability of N-trinitromethyl azoles is relatively higher than stability of similar C-trinitromethyl heterocycles. Replacing one nitro group in the trinitromethyl moiety with fluorine or difluoroamine group changes the C–NO2 bond length and the thermal stability. However, there is no linear correlation between the rate constants and the C–NO2 bond length, which indicates the presence of other factors affecting the stability of trinitro- and substituted dinitromethyl derivatives. The burning rates of the nitropyrazoles varied from 26.8 mm s−1 (for 1) to 77.5 mm s−1 (for 4) at 10 MPa. An analysis of thermocouple data shows that the burning rate of nitropyrazoles 1, 2, and 4 depends on the rate of heat release in the condensed phase. The increased stability of the fluorodinitromethyl compound 3 causes a decrease in the depth of its decomposition in the melt and shifts the leading reaction of its combustion into the gas phase. Two-stage decomposition is stipulated by different thermal stabilities of the substituent and the dinitropyrazole fragment