Study On Molecular Thermal Decomposition And Synthesis Reaction Mechanism Of Several Energetic Materials

As an important energetic material,energetic material is generally regarded as a metastable material with relatively high energy density,mainly fuel,explosive and propellant,etc.,playing an increasingly important role in national defense,industrial production,and other fields.With the rapid development of science and technology,people have more and more requirements for energetic materials.Good energetic materials need not only high energy density but also high stability.The development of energetic materials has been nearly one hundred years,but the research on their thermal decomposition and synthesis reaction mechanism is still relatively slow.This is a basic problem in the field of energetic materials,so the research on the thermal decomposition and synthesis reaction mechanism of energetic materials is particularly important.The Ab initio method can accurately describe bond changes in chemical reactions,clearly define reaction conditions,and has higher computational accuracy than general classical position dynamics,which is widely used in theoretical calculations related to chemical reactions.Based on density functional theory,the mechanism of thermal decomposition and cyclization of energetic materials is studied in this thesis.The main research contents and innovative achievements of this paper include:（1）The reaction mechanism of molecular pyrolysis of nitromethane has been extensively studied by scholars,but the initial reaction and the reaction path with a lower energy barrier in the initial thermal decomposition of nitromethane are still hot issues at present.The pathways in the initial thermal decomposition of nitromethane were studied by the Density function theory.It is found that in the early stage of the thermal decomposition reaction of nitromethane,the reaction between nitromethane molecules can generate catalytic intermediates.The catalytic process has a low energy barrier,so the catalytic reaction is easy to occur.The formation of stable small molecule products（H₂O,CH₄,CO₂,etc.）in the initial stage of reaction was verified by calculation.The chemical process of nitromethane in the initial stage of a thermal decomposition reaction is described accurately,which has a certain reference value for the study of molecular thermal decomposition of other energetic materials.（2）Large conjugated structures exist in the molecules of carbon-nitrogen heterocyclic energetic compounds,which reduce the sensitivity of explosives to a certain extent,so scientists pay special attention to it.In the experiments,carbon and nitrogen heterocyclic energetic compounds with good physical and chemical properties can be synthesized from nitroguanidine and glyoxal,urea and glyoxal respectively.However,the synthesis mechanism is not clear,and the temperature required by the two cyclization reactions and the yield of the product is quite different.In this paper,the mechanism of cyclization reaction of 4,5-dihydroxy-2-nitroiminoimidazolidine and 3,4-dihydroxy-imidazolidine-2-ketone was studied by the ab initio method according to the experimental conditions.By analyzing the calculated results,it is found that there are side reaction paths in both cyclization reactions.The main reason that the yield of 3,4-dihydroxy-imidazolidine-2-one is much lower than that of 4,5-dihydroxy-2-nitroiminoimidazolidine-2-one is not only the relatively high energy barrier but of the 3,4-dihydroxy-imidazolidine-2-one cyclization reaction path but also the stronger chemical driving force of side reaction path.The cyclization reaction mechanism of partial ammonia aldehyde condensation is explained,which is of great significance for the synthesis of polynitrocyclic compound.