Study On The Mechanism And Kinetics Of The Nitration Reaction During The Preparation Of Nitro-energetic Materials

The strength of national defense is one of the most important components of national comprehensive power,and is a strong backing for the national economy and social development.A strong national defense depends on the development of energetic materials with high-powered?low sensitivity,high energy density,and high reliability?so as to meet the increasing demands of the explosive materials?dynamites?and power energy materials?propellants?for various weapons.Nitro energetic materials are the most widely and massively used energetic materials in military field so far.The development of the nitro energetic materials has become one of the most important factors that influence or even constrain the comprehensive performance of weapons.However,the traditional energetic materials?such as TNT etc?are prone to explosion when they are stimulated by friction,impact,electrostatic spark or shock wave during the process of preparation,storage,transportation,and application.Thus,the insensitive energetic materials have increasingly become a hot topic in the field of energetic materials.Owing to the unique advantages over traditional ones,5-nitro-2,4-dihydro-1,2,4-triazol-3-one?NTO?,1,1-diamino-2-2-dinitrolene?FOX-7?and N-guanyl-2-nitro-amide?FOX-12?have become the typical representative of the insensitive energetic materials.Until now,the insensitive nitro energetic materials are mainly prepared via the nitration of proper substitutes in nitric-sulfuric acid system.While simultaneously,some severe defects?such as high risk,grievous equipment corrosiveness,massively discard acid and acidic waste water?are also found in such mixed acid system.Therefore,it is imperative to deeply explore the nitration mechanism and kinetics in the preparation of nitro energetic materials in order to develop safe,controllable,efficient,and environmental benign processes,which are firmly believed to have special significance to the national economy,social development and national security.This dissertation aims at the problems of low yield,poor safety,and serious enviromental pollution in the current research and application,and concentrates on the establishment of green,efficient and safe preparation of nitro energetic materials.The nitration mechanisms and kinetics in the preparation of insensitive energetic materials of NTO,FOX-7 and FOX-12 in the nitric-sulfuric acid were systematically studied by the quantum chemistry method along with the on-line monitoring technologies.Moreover,the mechanism of the green/efficient nitration of aromatics in ceric ammonium nitrate?CAN?system was also investigated.The main findings are summarized in four parts as follows.?1?The nitration mechanisms in the preparation of NTO in concentrated nitric acid system and nitric-sulfuric acid system were systematically investigated via the B3LYP/6-311G?d,p?method.The quantum chemical calculation method for the energy of each species was evaluated and optimized by a two-step calorimetry experiments.The canonical variational transition?CVT?state theory with small curvature tunneling?SCT?correction was used to calculate the rate constants of all elementary reactions.The possible nitration mechanisms,including NO₂⁺ direct nitration,NO₃^--induced nitration,and HSO₄^--induced nitration were presented.It is found that the energy barrier of the nitration system may distinctly decrease via the presented inductive effect of the acidic group,and thus promot the formation of NTO.Moreover,it is found that the acidic group-induced C-nitration pathway may be the most favorable way to occur.Compared with the promotion of NO₃^-in concentrated nitric acid system,the promotion of HSO₄^-in nitric-sulfuric acid system is more significant.Additionally,lower reaction temperature usually means less by-products and better selectivity during the nitration in both the concentrated nitric acid system and the nitric-sulfuric acid system.The acid concentration should also be well controlled so as to ensure that not only enough nitration reagent NO₂⁺ is generated,but also more acidic groups are simultaneously dissociated to induce and promote the nitration process.?2?The synthesis mechanism of FOX-7 in nitric-sulfuric acid system was systematically investigated by using the B3LYP/6-311G?d,p?method.The synthesis of FOX-7 involved in two processes of the nitration of 2-methyl-4,6-dihydroxypyrimidine?MDP?and the hydrolysis of nitration product?NMP?.In view that four-NO2 are needed in the nitration process of MDP,the introduced order of-NO2 may bring about the fluctuation of charge distribution in the corresponding pre-intermediates,resulting that the HSO₄^--induced preferential dinitration on methyl group become the most favorable nitration pathway of MDP. and increase the yeild of FOX-7.The induction effect of HSO₄^-in nitric-sulfuric acid The proposed induction of HSO₄^-may effectively promote/catalyze not only the NO₂⁺ attack,but also the H-transfer and H-abstraction as well,and thus dramatically decreases the activation free energy of the nitration system.Meanwhile,the induction of HSO₄^-can also effectively promote the hydrolysis of NMP and the decomposition of the hydrolysis product DMA.Therefore,the concentration of HSO₄^-is moderately improved to accelerate the preparation process system may promot not only the nitration of MDP,but also other reaction system involved in the activation of C-H,N-H,and O-H groups.?3?The nitration of NH₂SO₃M?M = 0,H,NH₄,Na,and K?is used as the model reaction in the synthesis of FOX-12 in nitric-sulfuric acid system.The mechanisms of five nitration models were systematically studied by the M06-2X/6-311G?d,p?method.The induction effect of HSO₄^-is also found to promot the nitration of NH₂SO₃M.The HSO₄^--induced preferential substitution-SO3 is the most favorable nitration pathway of NH₂SO₃M with the mixed acids.The active order of substrate in the nitration of NH₂SO₃M is NH₂SO₃->NH2S03H>NH₂SO₃NH₄>NH₂SO₃K>NH2S03Na.Moreover,such active order is also confirmed by the rate constants obtained via the TST/Eckart method.Although NH₂SO₃H has higher acitivity than other sulfamates in the nitration process,it is difficult to quickly and effciently dissociate the required NH₂SO₃-,which limits its application in the synthesis of FOX-12.?4?The nitration of acetanilide is used as a model reaction.The nitration mechanisms of aromatics in CAN system were systematically investigated by the M06-2X/6-311G?d,p?-SDD method.The nitartion mechanisms of acetanilide with CAN mainly include four pathways.They are N02+ nitration,-NO2 nitration,NO₃^-nitration,and-NO3 nitration.The-NO3 nitration mechanism is found to be the most favorable pathway both kinetically and thermodynamically.Moreover,the-NO3 nitration mechanism is also verified by the in-situ pH detection,free radical scavenger,and XPS experiments.The-NO3 nitration is a mechanism of the redox coupled with free racical.In the-NO3 nitration mechanism,Ce4+of CAN may act as a temporary electron accepter,and NO₃^-may provide the source of-NO2-In nitric-sulfuric acid system,the proposed acidic group-induced effect may contribute great to the better understanding of the nitration process,and provide the theoretical basis and guidance for the research and engineering amplification of the preparation of insensitive energetic materials.Based on the green nitration system of CAN,it is expected that the proposed NO3 nitration mechanism may also fit for other nitration systems when CAN is used as the reaction agent,which is expected to provide a theoretical and technical basis to the experimental investigation of the nitration in CAN system and the optimization of process condition.