1IntroductionPolyazido heteroaromaticc ompounds have currently been extensively studieda sh igh-density energeticm aterials in material science [1][2].These compounds possess high density [3],h igh positive heat of formation [4][5][6],g ood thermal stability [7,8],a nd thermodynamicallyf avorable decomposition [9] that the mainc ombustion product is typically nitrogen gas [10],w hich result in numerous unique applications such as solid fuels in micropropulsion systems [11],s mokefree pyrotechnic fuels [12],g as generators, effective precursors for carbon nanospheres [13] and carbon nitride nanomaterials [14,15].The introduction of an azido group playsavery important role in increasing the heat of formation (HOF) of energetic compounds [16].H owever, most of described polyazides sucha s2 ,4,6-triazido-1,3,5-triazine( TAT)a nd 3,6-diazido-1,2,4,5-tetrazine( DIAT) are so sensitivet owards hock, spark, friction, and thermal impulse [17][18][19][20] that their applications are extremely limited. Despite there are no precise data comparing the sensitivity of an azide to its isomeric tetrazole, the aromatic tetrazoles are generally less sensitive toward shock and friction than covalent azides. Therefore, the isomeric tetrazoles formed by 1,3-dipolar cyclization [21] of the polyazides are potential replacements for the sensitive polyazides.Hiskey's grouph as made progresso ni mprovingt he sensitivity of polyazidoh eteroaromatic compounds [22].T he unexpected azido-cyclization and irreversible tetrazolo transformation of DIATd ifferentf rom other polyazidoh eteroaromatic compounds was reported. Equilibria of diazidotetrazine with its monotetrazole and one of the isomeric di-tetrazole were observeda td ifferent temperatures in DMSO. Unfortunately,n either the isomeric products could be distinguished or separated the 13 CNMR spectroscopic data sufficient to support the predictionf or the azido-cyclization product. Furthermore, until now,c ompared with thet heoretical studies [21,[23][24][25][26],t he experimental studies on the azido-cyclization of DIATare few,w hich may be due to the difficulty in characterization and danger arising from their extremely high sensitivity [27].We herein report further experiments and results on the azido-tetrazolo tautomerizationso fD IATw ith HPLC and 13 CNMR in three kinds of representative solvents according to their polarity,C HCl 3 ,C H 3 OH and DMSO, respectively.T he unexpectedi rreversible transformation resulted 6-aminotetrazolo[1,5-b]-1,2,4,5-tetrazine (ATTZ) as the final product, is disclosed. After at hrough survey of literature, we found that Licht and Ritter [28] had reported the preparation of ATTZ in 1994, but no other physical properties or crystal structures were available. In this paper,anovel and more efficient approach for the synthesis of ATTZ is developed and its crystal structure and physical properties are reported.Abstract:T he azido-tetrazolo tautomerizations of 3,6-diazido-1,2,4,5-tetrazine (DIAT) in different solvents were investigated with HPLC and 13 CNMR spect...
