Synthesis And Characterization Of A Series Of Heat-resistant Explosives Derived From Fused-azines

With the increasing demands for high-energy insensitive explosives in military and civilian fields,nitrogen-rich energetic compounds have received extensive attention.Compared with traditional energetic compounds,nitrogen-rich energetic compounds have the following advantages:（1）There are a large number of N?N bonds,N-N bonds and C-N bonds in the molecules,which are conducive to the formation of high positive enthalpy of formation in energy storage;（2）The characteristics of high nitrogen content and low carbon and hydrogen content of polynitrogen compounds can not only increase their densities,but also make it easier to achieve oxygen balance;（3）The decomposition product is N₂,which is environmentally friendly.Therefore,the design and synthesis of nitrogen-rich compounds has received extensive attention in the field of energetic materials.The coplanar structure of six-membered nitrogen-rich fused ring（azines）makes it easier forπelectrons to delocalize and resonate to formπ-πstacking pattern.Moreover,nitrogen-rich fused-ring compounds have multiple chemical sites that can be modified by explosophores,which is beneficial to improve the detonation performances,densities and oxygen balances of energetic compounds.In this dissertation,a series of fused-ring heat-resistant explosives were synthesized and characterized by different analytical methods.The main research contents are as follows:（1）5,7-diamino-[1,2,5]oxadiazolo[3,4-d]pyrimidine,5,7-diamino-2H-[1,2,3]triazolo[4,5-d]pyrimidine and 2,6-diamino-9H-purine were oxidized under mild oxidation condition（TFAA/50%H₂O₂ or Ac₂O/50%H₂O₂）,respectively.Then three corresponding nitrogen-rich heterocyclic compounds were obtained.They are characterized by X-ray single crystal diffractometer,infrared spectrometer,nuclear magnetic resonance instrument and differential scanning calorimeter.These molecules all show high thermal stabilities,good detonation performances and low sensitivities（IS>40 J,FS>360 N）.Among them,2,6-diamino-9H-purine 1-oxide has the highest onset decomposition temperature（T_d）of309℃.T_dof compounds 5,7-diamino-[1,2,5]oxadiazolo[3,4-d]pyrimidine 6-oxide and5,7-diamino-2H-[1,2,3]triazolo[4,5-d]pyrimidine 6-oxide are 280℃and 303℃,respectively,indicating that they have potential application values as heat-resistant explosives（T_d>250℃）（2）Using inexpensive and easily available ethyl cyano（hydroxyimino）acetate as a starting material,via a simple three-step method,4-amino-3,8-dinitropyrazolo[5,1-c][1,2,4]triazin-7-ol was obtained,which contains a fused energetic skeleton of triazine and diazole,and NO₂/NH₂ and NO₂/OH as substituted groups.4-amino-3,8-dinitropyrazolo[5,1-c][1,2,4]triazin-7-ol was reacted with ammonia,hydroxylamine,98%hydrazine hydrate and potassium hydroxide aqueous solution,respectively,to obtain the corresponding energetic salts.In addition,using easily-prepared and air-stable potassium nitroacetonitrile（K-NAN）as an alternative,not only the reaction conditions become mild,the operation becomes safe and pollution-free,but also the total yield of the optimized scheme is improved to 46%.Neutral compound has an excellent onset decomposition temperature（T_d=332°C）and low thermal sensitivity(T_5s=380°C).In addition,4-amino-3,8-dinitropyrazolo[5,1-c][1,2,4]triazin-7-ol also shows good detonation performances(ν_D=8538 m·s^-1,P=30.4 GPa)and insensitivities（IS>40 J,FS>360 N）.（3）Based on the reaction of 6-（3,5-dimethyl-1H-pyrazol-1-yl）-[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazine with 3,5-dinitropyrazine-2,6-diamine under alkaline condition,an-NH-bridged planar energetic compound N²-（[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazin-6-yl）-3,5-dinitropyrazine-2,6-diamine was obtained.The structure was analyzed and characterized by nuclear magnetic resonance spectroscopy,infrared spectrum,single-crystal X-ray diffraction and other analytical methods.The measured density at room temperature is 1.70 g cm^-3,and the detonation performances areν_D=7568 m·s^-1 and P=23.5 GPa.In addition,its high decomposition temperature（T_d=255℃）and low sensitivity（IS=12.5 J,FS=240 N）enable it to be used as a heat-resistant explosive in the civilian industry.