From N-amino to N-azo derivatives: Influence of the structure of isomeric azo derivatives of dinitropyrazoles on their decomposition and combustion mechanism

The study investigates the thermal stability and combustion characteristics of isomeric 1,2-bis(dinitro-1H-pyrazol-1-yl)diazenes. The investigation of thermal decomposition revealed that over a wide temperature range, the activation energies for the decomposition of two isomeric molecules, 1,2-bis(3,4-dinitro-1H-pyrazol-1-yl)diazen (3,4-DNPAz) and 1,2-bis(3,5-dinitro-1H-pyrazol-1-yl)diazen (3,5-DNPAz), are relatively low: 145.2 and 134.6 kJ·mol -1 , respectively. It is suggested that the rate-limiting step is the isomerization of azo groups from the more stable trans form to the less stable cis form, rather than monomolecular N-N bond breaking. In the case of the 3,5-DNPAz isomer, the proximity of the nitro group to the azo linkage significantly facilitates the trans - cis isomerization reaction. The study of the combustion behavior of two isomeric azo compounds revealed an unusually large difference in their burning rates. Thermocouple studies indicated that the surface temperatures of 3,5-DNPAz are close to the surface temperatures of RDX, while the surface temperatures of 3,4-DNPAz are significantly higher. The combustion of isomeric azo compounds was found to follow different mechanisms, which are associated with the different thermal stabilities and volatilities of their parent dinitropyrazole isomers. Thermal safety predictions were made, and thermodynamic studies were conducted for azonitropyrazoles.