| High-nitrogen compounds have gained extensive attention due to their high nitrogen content,high positive heats of formation and release of environmentally benign nitrogen gas after decomposition.Based on tetrazole,a stable heterocycle with high nitrogen content,many series of high-nitrogen energetic compounds employing triazene,pentaza-1,4-diene and azoxy as linkages have been designed and synthesized.Firstly,a series of hypergolic fuels,?2-methyltetrazol-5-yl?diazotates?2-2,2-3,2-5-2-8?havebeensynthesizedbytreatmentofbaseswith?2-methyltetrazol-5-yl?diazotatic acid?2-1?,which were easily prepared by using isoamyl nitrite.All the salts decompose at a low to moderate onset temperature,ranging from 98°C to 209°C.The measured densities of diazotates range between 1.49?1.61 g·cm-3.Besides,all the diazotates exhibit high positive heats of formation(658.8?999.5 kJ·mol-1),high specific impulse?246.4?291.2 s?and short to moderate ignition delay times?12?62 ms?.Among them,the ammonium salt?2-2?and the hydrazonium salt?2-3?display the highest specific impulse,which are 281.1 s and 291.2 s,respectively,and shortest ignition delay times,which are 12 ms and 14 ms,respectively.Secondly,a series of 1,3-bis?tetrazol-5-yl?triazenes?3-2a?3-2k?were synthesized and subsequently transformed into 5,5'-azoxybistetrazoles?3-3b?3-3f,3-3i?in moderate to high yields.The synthetic method of 5,5'-azoxybistetrazoles is one-pot of two steps by using fuming nitric acid and acetic anhydride respectively,whose mechanism is proposed to be nitration,deoxygenative reduction and rearrangement in sequence.The physical and detonation properties of some 1,3-bis?tetrazol-5-yl?triazenes?3-2b?3-2d,3-2g,3-2h,3-2k?and 5,5'-azoxybistetrazoles?3-3b,3-3d,3-3i,3-3k?were investigated and compared.It reveals that the 5,5'-azoxybistetrazoles possess higher densities(1.57?1.68 g·cm-3)and impact sensitivities?0.1?0.5 J?than their triazene precursors(1.32?1.55 g·cm-3 and 0.75?5J,respectively).Besides,most of the 5,5'-azoxybistetrazoles exhibit higher detonation velocities(7228?8066 m·s-1)than triazene precursors(6138?7151 m·s-1).Among the5,5'-azoxybistetrazoles,2,2'-dihydroxyethyl-5,5'-azoxybistetrazole dinitrate?3-3d?shows the best predicted detonation performance(detonation velocity is 8066 m·s-1 and detonation velocity pressure is 25.8 GPa).Finally,Utilizing 1,3-bis?tetrazol-5-yl?triazenes as starting materials,the moiety of pentaza-1,4-diene has been constructed by activating triazenes with carbodiimide under mild conditions.Thus,a series of 1,3,5-tri?tetrazol-5-yl?pentaza-1,4-dienes?4-1a?4-1j?have been synthesized in moderate to high yields.All the pentazadiene compounds exhibit poor thermal stabilities with decomposition temperature in the range of 100?141°C and poor chemical stabilities with decomposition to amine and diazonium salt by treatment with acid.Most of them show low densities(1.40?1.58 g·cm-3)but high positive heats of formation(871.5?1699.2 kJ·mol-1).Particularly,1,3,5-tri?2-methyltetrazol-5-yl?pentaza-1,4-dienes?4-1i?displays excellent heats of formation up to 1699.2 kJ·mol-1 and good predicted detonation performance(detonation velocity is 8572 m·s-1 and detonation velocity pressure is 25.1 GPa).However,it is extremely sensitive to impact?0.25 J?. |
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