Study On The Mechanism Of Nitrolysis Of HA

HMX is one of the best single explosives in comprehensive performance among all kinds of single explosives which are used so far,and it is a kind of strategic materials which are always valued by all countries in the world.The acetic anhydride technique is a widely used preparation technique of HMX in industry,high cost,high energy consumption and low yield are the shortcomings of the technique.A further study of the nitrolysis mechanism of preparing HMX by the acetic anhydride technique and the effect of ammonium nitrate in the acetic anhydride system will greatly help us to improve the acetic anhydride technique and increase the yield of HMX.In this paper,the nitrolysis mechanism of HA in the acetic anhydride-nitric acid-ammonium nitrate-acetic acid system was studied in detail,the morphological structure of HA and DPT in the mixture system,the effect of ammonium nitrate in the reaction system and the reaction mechanism of each step of the nitrolysis of HA were studied using quantum chemistry.The structures of HAMN,the HAMN―NO₃^-complex and the HAMN―NO₃^-―NH₄⁺complex were studied using DFT-B3LYP method at the 6-311++G（d,p）and aug-cc-pVTZ level.The aim of optimizing molecular structure,calculating molecular total energy,calculating corrected dissociation energy of BSSE and calculating stable energy using NBO was to determine the main configuration of the molecular structures in the nitrolysis system,the molecular hybrid orbital type and the atomic charge distribution in the molecule were analysized using NBO calculation.There are two structures of HAMN,a and b.a salt is formed by hydrogen bond of N atom of HA and HNO₃,b salt is consisted by protonated HA and NO₃^-.The a type structure of HAMN is the stable structure,and the single crystal of a salt was prepared in the experient,the structure of the molecules of the single crystal which was detected by the X light diffraction experiment was consistent with the calculated result.There are seven stable structures of the HAMN―NO₃^-complex,the structure of a6complex is the stablest structure among the seven structures and the main complex structure in the system.There are three stable structures of the HAMN―NO₃^-―NH₄⁺complex,the structure of d2 complex is the stablest structure among the three structures and the main complex structure in the system.The bond length and bond order of HA,HAMN,the a6complex and the d2 complex were studied,we found that the NO₃^-can make two N-C bonds of an active N atom of HAMN weaken to the same degree and another N-C bond of the active N atom strengthen.As a result the two weak N-C bonds of the HAMN―NO₃^-complex are broken easily at the same time in the nitrolysis of the complex,the change of bond length and bond order make the needed energy of breaking bond decrease theoretically.The NH₄⁺and NO₃^-can make the three N-C bonds of an active N atom of the HAMN―NO₃^-―NH₄⁺complex be different bond strength,so the complex can only break a weakest N-C bond of three N-C bonds in the nitrolysis of the complex,which may theorily explain that the effect of ammonium nitrate added into the acetic anhydridec reaction system is advantageous to prepare HMX.At the 6-31G（d）level,the nitrolysis reaction of HAMN,the HAMN―NO₃^-complex and the HAMN―NO₃^-―NH₄⁺complex with CH₃COONO₂ was studied using DFT-B3LYP method,the reactions transition states were designed and optimized,the IRC reaction pathways connect reactants and products,the bond length of the main bonds which are involved in the nitrolysis process was analysed,which indicated the reactions are reasonable.The activation energy of the reactions were calculated,the nitrolysis activation energy of HAMN is 129.373 kJ·mol^-1;the nitrolysis activation energy of the HAMN―NO₃^-complex is 115.744 kJ·mol^-1;the nitrolysis activation energy of the HAMN―NO₃^-―NH₄⁺complex is 31.331 kJ·mol^-1.The calculated results indicated that the catalytic effect of NO₃^-is very small.One of two weaker N-C bonds of the attacked N atom of the HAMN―NO₃^-complex was found to be broken,and the other N-C bond was elongated too long to be broken closely in the IRC,which indicated the NO₃^-of the HAMN―NO₃^-complex is disadvantageous to prepare the eight-element ring HMX.The NO₃^-and NH4⁺the HAMN―NO₃^-―NH₄⁺complex can greatly reduce the reaction energy barrier in the nitrolysis process,and play a catalyzer role,and two weaker N-C bonds of the active N atom of the HAMN―NO₃^-―NH₄⁺complex were not found to be broken at the same time,or one bond was broken and the other was elongated too long to be broken closely were not found in the IRC too,which is advantageous to prepare the eight-element ring HMX.At the 6-31G（d）level,the nitrification of MNPM and it’s derivatives with CH₃COONO₂ was studied using DFT-B3LYP method,the reactions transition states were designed and optimized,the IRC reaction pathways connect reactants and products.The bond length of the main bonds which are involved in the nitrification process and the atomic charge change of the reactants,transition states and products were analysized,which indicated the reactions are reasonable.When we optimized the molecular structure of MNPM,we found that there are two structures of MNPM,and because of the large steric hindrance of MNPM,it is difficult to be nitrified by CH₃COONO₂,and the transition state of the nitrification of MNPM were not designed and optimized always.But,the esterification of MNPMⅡwith CH₃COONO₂ is very easy,and the product of the esterification can be MNPM nitric ester,the foreward reaction activation energy of the esterification is 25.934 kJ·mol^-1,the reverse reaction activation energy of the esterification is 99.389 kJ·mol^-1,the foreward reaction is very easy and can occur at room temperature.When we studied the intramolecular nitrification of MNPM nitric ester,we found there are two structures of MNPM nitric ester,one type is the nitrate type（reactant1）,the other type is the nitric ester type（reactant2）,the energy of the configuration conversion from the reactant 1 to the reactant 2 is 31.186 kJ·mol^-1.The foreward reaction activation energy of the intramolecular nitrification of MNPM nitrate is 204.138 kJ·mol^-1;the foreward reaction activation energy of the intramolecular nitrification of MNPM nitrate ester is 172.952kJ·mol^-1,the reverse reaction activation energy of the two intramolecular nitrifications is almost equal to 202.535 kJ·mol^-1.The intramolecular nitrification of the reactant 1 is carried out by converting it’s configuration to the reactant 2,which was found in the IRC,and resulting in DPT at last.The nitrification of MNPM nitric ester and MNPM acetate are not easy to occur,the two reactions energy barrier is very high,and the reactions can occur at higher temperature,but higher temperature is disadvantageous to the nitrolysis of HA.The structures of DPT,the DPT―NO₃^-complex and the DPT―NO₃^-―NH₄⁺complex were studied using the DFT-B3LYP method at the 6-311++G（d,p）level and aug-cc-pVTZ level.The aim of optimizing molecular structure,calculating molecular total energy,calculating corrected dissociation energy of BSSE and calculating stable energy using NBO was to determine the main configuration of the molecular structures in the nitrolysis system,the molecular hybrid orbital type and the atomic charge distribution in the molecule were analysized using NBO calculation.There are three stable structures of the DPT―NO₃^-complex,the structure of t3 is the main complex structure in the system.There is only one stable structure of the DPT―NO₃^-―NH4+complex.The DPT―NO₃^-complex and the DPT―NO₃^-―NH₄⁺complex can keep that the bridge C-N bonds of DPT weaker than the ring C-N bonds of DPT always.However,the NO₃^-of the DPT―NO₃^-complex makes a ring N-C bond length increase more which is adjacent to the bridge N-C bond,and the longer ring N-C bong is easy to be broken in the nitrolysis of the DPT―NO₃^-complex,which is disadvantage to prepare eight-elements ring intermediates.The NH₄⁺and NO₃^-of the DPT―NO₃^-―NH₄⁺complex can reduce the structural defects of the DPT―NO₃^-complex and make a ring N-C bond length increase less,and the ring bonds are not easy to be broken in the nitrolysis,which makes the weakest bridge bond be broken only in the nitrolysis process of the DPT―NO₃^-―NH₄⁺complex.Obviously the NH₄⁺and NO₃^-of the DPT―NO₃^-―NH₄⁺complex are favourable for preparing eight-element ring intermediates,and which can decrease the nitrolysis reaction energy barriers,the nitrolysis of DPT can be catalyzed by ammonium nitrate.The nitrolysis of DPT,the DPT―NO₃^-complex and the DPT―NO₃^-―NH₄⁺complex with CH₃COONO₂ was studied using the DFT-B3LYP method at the 6-31G（d）level,the reactions transition states were designed and optimized,the IRC reaction pathways connect reactants and products,the bond length of the main bonds which are involved in the nitrolysis process was analysized,which indicated the nitrolysis of DPT and it’s complex is reasonable.The nitrolysis activation energy of DPT is 224.957 kJ·mol^-1;the nitrolysis activation energy of the DPT―NO₃^-complex is 87.448 kJ·mol^-1;the nitrolysis activation energy of the DPT―NO₃^-―NH₄⁺complex is 68.710 kJ·mol^-1,the catalytic effect of the NO₃^-of the DPT―NO₃^-complex,the NH₄⁺and NO₃^-of the DPT―NO₃^-―NH₄⁺complex are evident,and the catalytic effect of NH₄⁺and NO₃^-is more obvious than the NO₃^-,and the difference of the foreward and reverse reaction activation energy of the latter is more than the former,which is favorable for the foreward reaction and preparing eight-element ring intermediates.In the IRC,it was found that the bond length of one ring N-C bond of the DPT―NO₃^-complex increases more to be broken closely when the bridging N-C bond was broken in the nitrolysis of DPT―NO₃^-complex,which is disadvantageous to preparing the eight-ring HMX.The nitrification of TNTM and it’s derivatives with CH₃COONO₂ was studied using the DFT-B3LYP method at the 6-31G（d）level,the reactions transition states were designed and optimized,the IRC reaction pathways connect reactants and products,the bond length of the main bonds which are involved in the nitrification process and the atomic charge change of the reactants,transition states and products were analysized,which indicated the nitrification of TNTM and it’s derivatives is very reasonable.The nitrification of TNTM and it’s derivatives is easier,the nitrification activation energy of TNTM is59.153 kJ·mol^-1;the nitrification activation energy of TNTM nitrate ester is 100.755kJ·mol^-1;the nitrification activation energy of PHX is 83.176 kJ·mol^-1.However,the intramolecular nitrification of TNTM nitrate ester is more difficult,the intramolecular nitrification activation energy of its is 222.187 kJ·mol^-1.The esterification of TNTM with CH₃COONO₂ is very easy,and the product can be TNTM nitrate ester,the esterification activation energy is 44.427 kJ·mol^-1.