Synthesis And Properties Of Energetic Salts Based On Nitropyrazole

Energetic materials are a class of energetic compounds containing explosive groups（single explosives）or mixtures containing both oxidizer and fuel（composite explosives,propellants,pyrotechnics）.They can release a large amount of energy and gas products through its own redox reactions.Traditional single explosives（such as TNT,RDX,etc.）have conflicts between energy and stability.Therefore,researchers have been focus on the design and synthesis of new energetic compounds.There are three modifiable carbon sites and one modifiable NH site on the pyrazole ring.Various types of pyrazole energetic compounds can be synthesized through the modification of these four sites,and energetic salts can be further prepared.Based on the reasonable matching of pyrazole-based anions/cations with different cations/anions,the performance control of pyrazole energetic salts is realized,and it is expected that new energetic compounds with excellent performance can be designed and synthesized.In this paper,the synthesis and performance of monocyclic and bicyclic nitropyrazole energetic salts have been studied.First of all,monocyclic pyrazole energetic salts were synthesized.Using 4-chloropyrazole as the starting material,two different nitrating reagents were used to synthesize 4-chloro-3,5-dinitropyrazole,and then it reacted with ammonia at high temperature to give ammonium salt of 4-amino-3,5-dinitropyrazole.Amination of ammonium salt of 4-amino-3,5-dinitropyrazole and the neutral molecule with THA and hydroxylamine-O-sulfonic acid to give 1,4-diamino-3,5-dinitropyrazole as the product.For the first time,hydroxylamine-O-sulfonic acid was used to directly aminate ammonium salt of 4-amino-3,5-dinitropyrazole.After the experimental conditions were optimized,the yield was improved,the reaction steps were shortened,and the use of hydrochloric acid was avoided.Four new 1,4-dinitramino-3,5-dinitropyrazole energetic salts were prepared from 1,4-diamino-3,5-dinitropyrazole by nitration,acid-base neutralization and ion exchange reaction and have been fully characterized and analyzed.The structure was characterized using ¹H NMR,¹³C NMR,elemental analysis,and infrared spectroscopy.In addition,single crystal X-ray diffraction was used to determine the structures of energetic salts 2.8～2.10.The densities of these energetic salts（2.6,2.8～2.10）ranged between 1.572 to 1.800 g cm^-3.Their thermal decomposition temperatures ranged between 93.4 to 175.7℃and were measured by thermogravimetric analysis-differential scanning calorimetry.Their enthalpy of formation were calculated by Gaussian 09 software to be between 193.4 and 613.2 k J mol^-1.The impact sensitivity and friction sensitivity of these energetic salts were between 1.5～39 J and 54～360 N.These energetic salts were measured by impact sensitivity instrument and friction sensitivity instrument.The Hirshfeld surface and the 2D fingerprint region of the energetic salts 2.8～2.10 were studied by Crystal Explorer 17.5 software,the interaction between different atoms in them was analyzed.According to the Kamlet-Jacobs equation,their detonation velocity and detonation pressure were calculated to be between 7638～8982 m s^-1and 23.8～35.1 GPa,respectively.Their detonation heat were between 1229～1335 J g^-1.The oxygen balance（CO₂）were between-35.1%～-10.3%.Among them,the energetic salt 2.10 has good detonation performance and sensitivity,and were expected to be used as green primary explosive.The density of energetic salt 2.6 reaches 1.800 g cm^-3,and the detonation performance(P=35.1 GPa,D=8982 m s^-1)is close to RDX(P=38.0 GPa,D=8983 m s^-1),and the sensitivity is low（IS=12 J,FS=120 N）,it is expected to be used as secondary explosive.Bicyclic pyrazole is a combination of two monocyclic pyrazoles with different bonding methods such as C-C,C-N or N=N.Then energetic salts of bicyclic pyrazoles havebeendesignandsynthesizedbyus.Wedesigned4,4’-azo-bi（1-hydroxy-3,5-dinitropyrazole）,4,4’-azo-bi（1-nitramino-3,5-dinitropyrazole）and their energetic salts,the corresponding synthetic routes have been drawn up,the relevant synthetic researches have been carried out.First,4,4’-azo-bi（3,5-dinitropyrazole）was used as the starting material,and it was N-hydroxylated with Oxone.As a result,the starting material was not converted.Secondly,ammonium salt of1-hydroxy-4-amino-3,5-dinitropyrazole was used as the starting material,and potassium permanganate is used for azotization,the crude products have multiple points and the yield wereextremelylow.Thenweexploredthesynthesisof4,4’-azo-bi（1-nitramino-3,5-dinitropyrazole）.First,4,4’-azo-bi（3,5-dinitropyrazole）was used as the starting material,the THA reagent was used for amination.As a result,the crude product had multiple points and similar polarity,which was difficult to separate.In addition,we are trying to use 1,4-diamino-3,5-dinitropyrazole as a starting material to prepare 4,4’-azo-bi（1-nitramino-3,5-dinitropyrazole）,a new method for preparing sodium salt of nitrocyano-1,2,3-triazole by using 1,4-diamino-3,5-dinitropyrazole as a starting material to produce a new rearrangement reaction in the presence of an oxidizer was discovered.