Synthesis And Structure-property Relationship Study Of Energetic Compounds Based On Amphoteric Triazine N-oxides

As a special energy source,energetic materials（EMs）have a wide range of irreplaceable applications in national defense and civilian purposes.Only when the development of new EMs focuses not only on the improvement of performance,but also on the convenience of synthetic routes,can the obtained new EMs replace traditional energetic compounds.N-oxidation and ionization of nitrogen-rich EMs are important methods to improve their performance and enhance their development efficiency,respectively,but there were few studies on the synthesis and properties of energetic N-oxides and ionized products of triazine nitrogen-rich compounds.Moreover,the special studies on the synthesis and properties of amphoteric energetic compounds which can increase the development efficiency of ionic EMs also remain scarce.In this paper,a series of triazine nitrogen-rich industrial chemicals and their derivatives were selected as starting materials of N-oxidation,and triazine industrial chemicals melamine and acetoguanamine were transformed into three amphoteric triazine N-oxides when the probability and conditions of N-oxidation for the triazine industrial chemicals were being explored.Then,the three amphoteric triazine N-oxides were further transformed into 31 ionic EMs with diverse functions when their amphoteric properties were being studied.This work enriched the types of energetic N-oxides and amphoteric energetic compounds and provided a low-cost and highly efficient development route for new EMs.In this paper,the synthesis mechanisms,crystal structures,thermal decomposition and thermal properties and application performance of the obtained series of EMs based on the three amphoteric triazine N-oxides were studied in detail through experimental measurement and quantum chemical calculations,and on the basis of these studies,the general structure-property relationships of the products were analyzed.The substituents have a great impact on the N-oxidation of triazine compounds.The strong electron-donating substituents are in favor of the N-oxidation of triazine compounds,and the hydrazino groups and the unsubstituted triazine rings can perform oxidation-reduction and electrophilic substitution reactions with peroxy-acids,respectively.The N→O bonds can be easily protonated,which can expand the cationization pathway for energetic compounds.Because the O←N=C-NH₂ structure can tautomerize into the HO-N-C=NH structure,the O←N=C-NH₂ structure which has widely existed in energetic N-oxides can give energetic compounds amphoteric properties,whereas the similar O←N=C-OH structure cannot give energetic compounds amphoteric properties by itself because it mainly exists in the keto form HO-N-C=O.In addition to the dominant strong hydrogen bond interactions,π-πstacking,lone-pair-electrons-π,anion-πand weak?interactions,which theπ-electron deficient triazine rings tend to be involved in,are also important contributing factors of the formation of product crystals including energetic cocrystals.The synthesized series of EMs based on the three amphoteric triazine N-oxides showed diversified properties.Their thermal decomposition temperatures（T_d）are in the range of169～350℃,detonation pressure and detonation velocity are in the ranges of 11.2～40.7 GPa and 4899～9180 m s^-1,respectively,and impact sensitivities（IS）are in the range of 2.0～>23.5J.Moreover,a synthesized energetic silver salt decomposes easily under light exposure.The initial thermal decomposition mechanism of the three amphoteric N-oxides（T_d>285℃）and their heat-resistant metal-containing deprotonated products（T_d>280℃）may be the cleavage of nitrogen-oxygen bonds,and those of the metal-containing deprotonated products and the metal-free ionized products with relatively low thermal stability may involve the cleavage of coordinate bonds involving metal ions,the interionic hydrogen transfer and the direct decomposition of high-energetic anions.Oxygen balance（OB）is the most important factor affecting the detonation performance of the synthesized series of products.The detonation performance of each synthesized series of EMs increases with the increase of OB obviously.Compared with the non-protonated products,the detonation performance and IS of the protonated products with high OB are higher in general.Energetic cocrystals can not only decrease the sensitivities of their more energetic pure components,but also significantly increase the thermal stability of the components whose initial thermal decomposition mechanism may be the interionic hydrogen transfer,and energetic cocrystals which are composed of ionic and nonionic energetic compounds and have superior OB than their components can overcome the detonation performance trade-off disadvantage.Six synthesized energetic lead and copper salts all showed obvious catalytic effects on the thermal decomposition of two main energetic components of solid propellants.In addition,the structure and performance of an unexpectedly obtained long-chain nitrogen-rich energetic compound were also investigated.According to the different properties,the application orientations of the synthesized series of EMs based on the three amphoteric triazine N-oxides can involve heat-resistant insensitive explosives,high explosives,oxidants for solid propellants,green primary explosives,combustible agents for gas generating agents,energetic combustion catalysts,etc.,exhibiting the great potential of amphoteric energetic compounds,especially those with balanced amphoteric properties,in enhancing the development efficiency of new EMs.In addition,this paper presented methods of predicting the N-oxidation products of nitrogen-heteroaromatic compounds by quantum chemical calculations,which may be helpful for the synthetic development of more energetic N-oxides in the future.