The Reaction Mechanism And Kinetics Of Sulfamate And Aromatic Hydrocarbons In Mixed Acid System

Ammonium dinitramide?ADN?is a typical representative of high energy oxidizer,is used as a solid rocket propellant with the advantages of large gas volume,high energy,low characteristic signal and no chlorine,and has wide application prospect in conventional weapons and equipment.Until now,ADN is mainly prepared via the nitration of sulfamates in nitric-sulfuric acid system.So far there is no consensus on the synthesis mechanism.The absence of a detailed synthesis mechanism of ADN hinders its further study and application to a large extent.In nitric-sulfuric acid system,the investigation of nitration mechanism is mainly focused on the nitration of aromatic at present.The nitration mechanism of aromatics is found to be a typical mechanism of electrophilic substitution in organic chemistry.The induction effect of coexistence HSO4-in nitric-sulfuric acid system is found and proposed in our previous work.Such induction effect can promote the target nitration.We suppose that such induction effect may also exist in the nitration of aromatic in nitric-sulfuric acid system.Therefore,the nitration mechanism as well as kinetics of sulfamates and aromatics is systematically investigated in the present work.This thesis is expected to contribute a better understanding of the nitration mechanism,and provide theoretical basis to the research and engineering amplification of the preparation of energetic materials.The nitration mechanisms of sulfamates and aromatics in nitric-sulfuric acid system are systematically investigated by density functional theory?DFT?.Moreover,the rate constants of all elementary reactions are calculated by conventional transition state theory?TST?combined Eckart tunnel effect.The relation of rate constants with temperature and substrates are also discussed in two nitration systems.The main conclusions are summarized as follows:?1?The nitration thermodynamics,mechanisms and kinetics of NH₂SO₃R?R=H,NH4,Na,and K?are systematically investigated in gas and solvent phase via M06-2X/6-311G?d,p?method.NH₂SO₃Na and NH₂SO₃NH4 are the most favorable substrate in gas and solvent phase,thermodynamically.This result indicates that the solvent effect may significantly impact on the nitration thermodynamics.The nitration of NH₂SO₃R mainly involves in the direct nitration,HSO4--induced preferential substitution-SO3?pathway A?and-H?pathway B?nitration pathways.The inductive effect of HSO4-is found to effectively reduce the active free energy,and promote the nitration of NH₂SO₃R in nitric-sulfuric acid system.NH₂SO₃K is kinetically the most favorable substrate in gas and solvent phase.This prediction is in good agreement with the preparation experiment of ADN.Therefore,the nitration of NH₂SO₃K may be mainly controlled by kinetics.The optimized structures of all species and the active energies in all pathways is found to be close in gas and solvent phase,indicating that the solvent effect is not significant in the nitration of NH₂SO₃R.?2?The nitration mechanisms and kinetics of benzene?-H?,the aromatics of electron-donating group?-NH2,-OCH3,-OH,and-CH3?,and the aromatic of electron-withdrawing group?-Cl,-COOH,-CHO,and-NO2?are investigated in nitric-sulfuric acid system via M06-2X/6-311G?d,p?method.The nitration selectivity?ortho,meta,para?of the substituted aromatics are systematically discussed.The inductive effect of HSO4-may effectively reduce the active free energy,and promote the nitration of aromatics in nitric-sulfuric acid system.In the HSO4--induced mechanism,the nitration regioselectivity of the electron-donating group of aromatics is found to be an orientation effect of ortho and para.While the nitration regioselectivity of the electron-withdrawing group of aromatics is a meta-position effect?expect for chlorobenzene?.Moreover,the active free energies of the nitration of aromatics can be gradually deceased?increased?with the increase of the ability of the electron-donating?electron-withdrawing?group.Therefore,the stronger the ability of the substituted group donates electron,the higher the reaction activity may be obtained in the nitration of aromatics.