Quantum Chemical Studies Of Mechanisms For The Cyclization Reaction Of TKX-50

Finding new high-energy insensitive materials to replace traditional ammonium nitrate explosives has been a hot research topic in the field of energetic materials in recent years.As a high-energy insensitive ion salt with outstanding performance,1,1'-dihydroxy-5,5'-bitetrazole dihydroxylamine ammonium salt?TKX-50?has received a lot of attention.Many studies have been made on the synthesis,reaction conditions,properties and characterization of TKX-50.However,the reaction mechanisms for the synthesis of TKX-50 are still unclear,with few reports found in the literature.The cyclization reaction of 1,1'-dihydroxy-5,5'-bitetrazole?H₂DHTB?by diazonium diazide oxime?DAzGO?is the key step in the synthesis of TKX-50.In this thesis,the DFT method was chosen to study the reaction mechanisms of the key step.The structures of the reactants and products were optimized,and the transition states of two elementary reactions and the structure of an intermediate were found by MCD calculation and IRC calculation.By analyzing the structures of the reactants,transition states and intermediates,including key bond lengths,bond angles and dihedral angles,we confirm that the cyclization reaction of diazidoethylenediazine is a two-step cyclization reaction.The reaction energy barriers of the two-step cyclization reaction under vacuum conditions are 20.78kcal·mol^-1 and 15.77 kcal·mol^-1,respectively.The effects of water molecules and hydrogen ions on the reaction were investigated.Calculations show that the water molecules together with the hydrogen ions ring with the hydroxyl of DAzGO by hydrogen bond,reducing the energy of the reaction system.The cleavage and formation of hydrogen bonds promotes cyclization reaction of DAzGO.The hydrogen ions and water molecules reduce the energy barrier of the elementary steps by 7.3kcal·mol^-1 and 1.7 kcal·mol^-1.Water molecules and hydrogen ions promote the cyclization reaction.Five common solvents,acetone,diethyl ether,N,N-dimethylformamide?DMF?,ethanol and water were chosen to calculate the solvation free energy and energy change of the different models.For all reaction models,the reaction exhbits the lowest barrier when diethyl ether is employed as the solvent.Polarity of the solvent affects the reaction.Among these solvents,diethyl ether,for its lowest polarity is the best solvent for the cyclization reaction of DAzGO,and a solvent with similar polarity as diethyl ether may be a substitute for the reaction solvent.A model of N-hydroxymethyldialkylamine was constructed,and the reaction mechanisms of N-hydroxymethyldialkylamine nitrosation reaction were studied.NH₃ promotes the nitration reaction by capturing H of the hydroxyl.The complete reaction mechanisms of N-nitrosomorpholine formation by N-hydroxymethyldialkylamine in HNO₃/NH₄NO₃ system were speculated.