Broken-Symmetry Density Functional Theory Study on Pyrolysis Mechanisms of 3-Nitro-1,2,4-triazol-5-one (NTO)

Homolytic cleavage of covalent bonds is very common during the pyrolysis of energetic molecules. However, instead of locating the transition state and calculating the free energy barrier.G, the bond dissociation energy (.H, BDE) is usually considered as the energy barrier of the homo-cleavage processes. This simplification brings large errors. In the present work, several pyrolysis pathways of 3-nitro-1,2,4-triazol-5-one (NTO) were studied using broken-symmetry density functional theory method (BS-UB3LYP/6-311+G**). Each transition state of homolytic cleavage was located. The results show that the best pyrolysis pathway under the experimental conditions proceeds via the homolytic cleavage of the C-NO2 bond and the subsequent radical recombination, the energy barrier of the rate-determining step is 216.9 kJ center dot mol(-1) (523 K). Then, NO can promote the subsequent ring-opening, and finally yielding HNCO, N-2O and CO. Further reactions between these small molecules lead to NO2, N-2 and CO2. These products are consistent well with the experimental observations.

Automated summary

Homolytic cleavage is a common process in the pyrolysis of energetic molecules. This study investigated the pyrolysis pathways of 3-nitro-1,2,4-triazol-5-one (NTO) using density functional theory. The results showed that the best pathway involves the homolytic cleavage of the C-NO2 bond followed by radical recombination, leading to the formation of HNCO, N-2O, and CO. Further reactions between these small molecules result in the production of NO2, N-2, and CO2, consistent with experimental observations.