Theoretical Study On HMX Produced From TAT Nitrating By N₂O₅/HNO₃

Improving the yield and reducing the production cost of energetic material1,3,5,7-tetranitro-1,3,5,7-tetrazocycloctane（HMX）has been a problem in the past decades.The method for the HMX produced from the1,3,5,7-tetraacetyl-1,3,5,7-tetraazacyclooctane（TAT）is one of the most promising ways to replace the acetic anhydride method in synthesizing HMX,and the advantages of mild reaction,fewer by-products,and high product recovery make it with much more competition.However,the difficulty of TAT nitrification and the differences existing in the nitrification rates at each step have not been researched theoretically.To provide some theoretical guidance for the synthesis of HMX in experiments,density functional theory（DFT）was used to study the mechanism of nitration from the TAT to synthesize the HMX.In this paper,The DFT method was first applied in this article to study the reaction mechanism of N₂O₅/HNO₃in the nitration of TAT to prepare HMX in the aqueous solvent environment.The calculation revealed that there are two different nitrification modes in the first step of NO₂⁺nitration of TAT,namely nitrating acetyl oxygen atom and nitrating ring skeleton nitrogen atom.The former is more prone to occur,but the spontaneous nitration of TAT acetyl oxygen atom products can react with NO₃^-to generate the initial reactant TAT.Due to the large consumption the NO₂⁺in the above process,it will affect the occurrence of the TAT ring skeleton nitrogen atom nitration reaction.After forming the main product of Step 1,its further nitrification direction tends to be para rather than ortho.Finally,our calculations demonstrate that the nitration reaction rate of the ring skeleton nitrogen atom is determined by the reaction driving force of the unstable intermediate and the energy barrier for the stable intermediate to undergo forward reaction.The calculated results are in good agreement with the experimental results.Secondly,the DFT method was used to study the reaction mechanism of N₂O₅/HNO₃nitrating TAT to prepare HMX in the ionic solution environment.The intermediate formed by each step of nitrating the TAT’s ring skeleton nitrogen atom in the ionic solution environment is stable,which means that the nitration reaction rate of each step of the TAT’s ring skeleton nitrogen atom is different from that in the aqueous solution environment.The calculation results indicate that the ionic solution environment is more conducive to the synthesis of HMX by nitrating TAT than the aqueous solution environment.The main factor in the ionic solution environment is the energy barrier for the stable intermediate to undergo a forward reaction.Finally,the effects of three different anions on Step 1 and Step 2 in the ionic liquid environment were studied,and the calculation results showed that HSO₄^-was the most unfavorable for the smooth progress of these two steps.