Preperation And Theoretical Investigation Of Aromatic Compound-based Cocrystal Explosives

When two or more neutral species are combined via intermolecular interaction to form a new crystal structure,cocrystals are created with distinct physicochemical properties.Through cocrystallization,the detonation performance,sensitivity,and some other properties of the explosive can be modified.The previous studies show that the-CH�O type hydrogen bond,?-? stacking,and electrostatic interaction are the main driving forces for cocrystal explosive formation.However,those studies do not involove kinetic factor,including solvent effect,and so on.So,it has a great limit in the new cocrystal explosive design and preperation.In this paper,the cocrystal formation mechanism was investigated via solid-phase reaction.On the basis of thermal analysis data,we proposed a criterion for the cocrystal formation,and it is beneficial for the coformer screening.Moreover,focusing on the three kinds of intermolecular interaction,the preperation and formation mechanism of several aromatic compound-based cocrystal explosives were investigated.The main contents are as follows:Based on the experimental crystal structure,DFT(Density Functional Theory)calculation was performed to study the binding energy,intermolecular interaction,thermodynamic property,detonation performance of CL-20(2,4,6,8,10,12-hexanitrohexaazaisowurtzitane)/TNT(2,4,6-trinitrotoluene)cocrystal at M062x/6-311+G(d,p)level.The result shows-CH�O type hydrogen bonding is the main driving force for the cocrystal formation.The detonation performance of the cocrystal is better than that of the physical mixture of CL-20 and TNT in a molar ratio of 1:1 Based on the conclusion,a novel cocrystal of CL-20/TEX(4,10-dinitro-2,6,8,12-tetraoxa-4,10-diaza-tetracyclododecane[5.5.0.05.9.03,11)was designed.The same calculation method was employed to investigate the binding energy of different complex and the intermolecular interaction between CL-20 and TEX.The thermodynamic property,crystal structure,and detonation performance were also predicted.Similarly,-CH�O type hydrogen bonding plays a key role in the formation of the cocrystal.The detonation performance of the cocrystal is between CL-20 and TEX,and its sensitivity is lower than pure CL-20.The thermodynamics calculation shows that low temperature will be benefit for the cocrystal formation.A lot of experiments were carried out,while we did not get the CL-20/TEX cocrystal yet.This phenomenon suggests that intermolecular interaction can be used as an indicator,but there exists limitation.Molecular dynamics simulation was used to study the difference between physical mixture and cocrystallization of TNT/CL-20.The results show that maximum trigger bond length,trigger bond energy,and cohesive energy density may be utilized as criterion to judge the relative sensitivity for simple explosive and cocrystal.Based on the experimental crystal structure of BTF(benzotrifuroxan)/TNA(2,4,6-trinitroaniline)cocrystal,the behavior of the crystal structure,molecular structure,and electronic structure under hydrostatic pressure at 0-100 GPa was investigated within CASTEP code.The results show that the crystal and electronic structures change all of a sudden in the region of 40 GPa and 79-83 GPa,indicating the phase transition at those pressure.In addition,when the pressure reachs 83 GPa,new chemical bonds were found.Discover code was utilized to study the mechanical property of BTF/TNA cocrystal at different temperature.The results suggest the cocrystal has a better ductility at lower temperature,while it has the best tenacity at 295K.Using ?-? stacking and hydrogen bond as the design idea,styphnic and picric acid were used as the host nmolecules and many cocrystal coformers were chosen to get the corresponding cocrystal.Finally,styphnic/1,4-dioxane and picric acid/acetophenone solvates were obtained by solvent method.The structural analysis shows hydrogen bonding is the main driving force for the formation of styphnic/1,4-dioxane solvate.In picric acid/acetophenone solvate,there exists both hydrogen bonding and ?-? stacking.DFT calculations indicate ?-? stacking is stronger than hydrogen bonding.In order to study the competition between electrostatic interaction and halogen bond or hydrogen bond,four solvates containing TCTNB(1,3,5-trichloro-2,4.6-trinitrobenzene)or TBTNB(1,3,5-tribromo-2,4,6-trinitrobenzene)were designed and synthesized.MEP calculation shows that the competition between halogen bonding and electrostatic interaction is the main reason for the different crystal structure.A novel co crystal of TNB(1,3,5-trinitrobenzene)/NNAP(1-nitronaphthalene)was synthesized by solution method.The crystal structure shows a layer structure constracted by TNB and NNAP molecules.This kind of crystal structure is helpful to dilute the external force.Through a systematic study of solvate or cocrystal,we can have a deeper understanding of the intermolecular interaction and crystal structure.It also can provide some guidance for the cocrystal design and preparation.Cocrystls of TNT/NNAP,TNP(2,4,6-trinitrophenol)/NNAP,and TNB/NNAP were prepared by grinding method.The formation process of the cocrystals was monitored by XRD,FTIR,and DSC.Taking TNT/NNAP for example,with the grinding process going on,TNT and NNAP molecules stack on the {2-11} crystal face of the cocrystal.In fact,{2-1 1}crystal face is almost parallel with the benzene ring of TNT and the naphthalene ring of NNAP,indicating that ?-? stacking plays an important role in the cocrystal formation.The FTIR spectroscopy shows that the bending vibration of C-N-O in TNT is blue shifted because of the formation of hydrogen bonding.Due to the effect of ?-? stacking,the bending vibration of C-C in the benzene of TNT shift to the lower frequency.The C-H in the benzene ring takes part in the hydrogen bonding in the pure TNT,while no hydrogen bonding was observed in the cocrystal.DSC was utilized to study the phase transition in the TNT/NNAP cocrystal formation process.The melting point of the cocrystal was determined to be 65 ?.The cocrystal explosive formation mechanism is further understood through the analysis of the intermediate based on the solid-phase reaction.What's more,explosive-explosive cocrystal was prepared by grinding for the first time to the best knowledge of we known.It provides a fresh idea for the cocrystal explosive preparation.Three systems,including CL-20,NNAP,and BTF,were utilized to vertify the applicability of DSC method in cocrystal coformer screening.The two compounds were physically mixed at a molar ratio of 1:1.Then,the DSC curves of the mixture were recorded at a certain heating rate.The characteristic peak at the DSC curves were utilized to judge the cocrystal formation.The results show that the thermal behavior of each system is not thesame,but exothermic peak associated with cocrystal formation was observed in all the DSCcurves.The final products were identified by XRD and it has the same patterns with the cocrystal.Therefore,we can deduce that DSC method can be employed in the coformer screening of cocrystal explosive.Based on this method,a new candidate for BTF was chosen.The cocrystal was obtained by grinding method,and it was characterized.by PXRD.Meanwhile,solution method was used to get the cocrystal,the crystal structure was determined by single crystal X-ray diffraction.DSC method can remove the interference of the solvent effectively when we screen or prepare the cocrystal explosive.Compared to the other methods,it is more effective,accurate,and environment friendly.