Design,Synthesis And Mechanism Studies On The Tetrazole-Based High-Nitrogen Energetic Compounds

The tetrazole compounds have the advantages of high nitrogen content,positive heats of formation,good stability,clean product and being easy to adjust,etc.In order to explore new high-energy insensitive green energetic materials,in this paper,we took tetrazole-based high-nitrogen energetic compounds as the object,carried out a series of researches on molecular design,preparation and characterization,performance estimation and testing,and reaction mechanism.The main content is as follows:(1)The molecular structures containing the long nitrogen chain(N?6)were constructed by using tetrazole as the basic framework,and rich functional groups were introduced.Four series of 24 new tetrazole-based high-nitrogen energetic compounds were firstly designed.The geometrical optimization,electronic structure and vibration analysis were studied by first principle calculations.The density,heat of formation,energetic properties and impact sensitivity were predicted by the empirical formula.Results show that the heats of formation of most compounds are above 1000 k J/mol,of which HNBTz Tr is up to 1625.31 k J/mol.The densities of TNTz Tr,HNBTz Tr,N10-1 and N10-3 are comparable to that of CL-20(2.04 g/cm~3).The detonation heats of most compounds are higher than that of CL-20(1567 cal/g),of which N10-10 is 1833 cal/g.The range of detonation velocity is 8.60?9.94 km/s,and the range of detonation pressure is 32.04?47.30GPa.Overall,8 new compounds(DNOTz Tr TNTz Tr,HNBTz Tr,DNABTz,N10-1,N10,N10-9 and N10-10)exhibit the explosion performance comparable with HMX(D=8.75km/s,P=34.70 GPa).Thereinto,the compounds with OB being equal to zero(TNTz Tr,HNBTz Tr and N10-10)are close to CL-20(D=9.38 km/s,P=44.10 GPa),which can be potential candidates of high-energy green energetic materials.(2)Based on the 1,1'-dinitramino-5,5'-bitetrazolate(DNABT),7 novel DNABT high-nitrogen energetic salts were firstly designed and synthesized.The molecular structures were characterized by elemental,infrared spectroscopy and mass spectrometry.The crystal structures were firstly determined by the X-ray single crystal diffraction analysis.Thermal stabilities were studied by the DSC technology.The heats of formation were calculated based on the isodesmic reaction and the Born-Haber energy cycle.The detonation performance was estimated by using EXPLO5 6.01 program.The impact sensitivity and friction sensitivity were measured as well.Results show that DNABT salts have positive heats of formation(407.0?1377.9 k J/mol)with triaminoguanidinium salt(4)as highest one.The range of density is between 1.62 and 1.77 g/cm~3 of which diaminouronium salt(5)is the highest.Compared to neutral molecule,these energetic salts show higher thermal stability(180?210.5oC)with guanidinium salt(1)as the highest one.They also have high detonation velocity(8.18?8.71 km/s)and detonation pressure(24.3?32.3 GPa),suitable impact sensitivity(2.5?4.9 J)and friction sensitivity(40?120 N).Thereinto,triaminoguanidinium salt(4),diaminouronium salt(5)and3,4-diamino-1,2,4-triazolium salt(6)exhibit excellent comprehensive performance and are expected to be an alternative to RDX.(3)The azido cyclization mechanisms of tetrazolo-tetrazole,triazolo-bistetrazole and bistetrazolo-tetrazine were theoretically studied for the first time.The geometrical optimization,NBO charge and vibration frequency of each stationary point were calculated by using the DFT method.The effects of solvent on the reaction were investigated by using the SCRF theory and the PCM model.The transition states of each reaction were confirmed by the IRC calculation.The potential energy curve,the rate constant and Arrhenius equation were obtained by TST calculation.Results show that,for the reactions of azido cyclization into tetrazole,the electron transfers from the parent to the azido promoting the formation of the ring.The reaction energy barrier is below 40 kcal/mol,indicating that these reaction are feasible theoretically.In the two steps of cyclization,the first step of most of the reaction is easier,and 1,2,4-triazole is easier than 1,2,3-triazole.The second step is relatively difficult as a result of effect of the electron and space.The polar solvent DMSO can reduce the reaction energy barrier,especially for the first step.The energy barrier of rotational reaction for the azido group is very low,indicating that both3,6-diazido-1,2,4,5-tetrazine and its intermediate products have cis-trans isomerizations.The obtained kinetic data provides a theoretical basis for the experimental study of the azido cyclization.