The Molecular Designing,Synthesizing And Properties Of Triazolone Energetic Compounds

Triazolone derivatives have received increasing attention due to their high positive heats of formation and high nitrogen content,which can be used in potential energetic materials and intermediates of preparing high-energy explosives.Due to their significant importance,design and synthesis of rich-nitrogen compounds with novel structures and better performances are essential to the development of novel energetic compounds.The geometric structures of nitro-triazolone derivatives,such as 1,3,5-3H-1,2,4-triazol-5-one（TO）,4-amine-1,2,4-triazol-5-one（ATO）,3-nitro-1,2,4-triazol-5-one,and4,4’-azo-bis（1H-1,2,4-triazole-5-one）（ZTO）were fully optimized by the density functional theory（DFT）B3LYP/6-311+G**level.The electronic structures,band gap,heat of formation,densities and detonation properties were also studied.The reactivity of the aromatic C–H and N–H of ATO,NTO,and ZTO were discussed.The products obtained under the different nitrating agent werecharacterized by IR,NMR,MS,and EA.Then the crystal structures of title compounds were determined by X-Ray,and the evaluation of thermal hazards and thermo-kinetic parameters of title compounds were studied by the differential scanning calorimetry（DSC）,thermogravimetric-differential thermal analysis（TG-DTA）,and accelerating rate calorimetry（ARC）.The ring of ATO,NTO and ZTO nitro derivatives molecules has a certain aromaticity.Bond dissociation energies（BDEs）of the weakest bond N–NO₂ of compounds1,4-dinitro-1,2,4-triazol-5-one（III）,3,4-dinitro-1,2,4-triazol-5-one（VIII）,1,3,4-trinitro-1,2,4-triazol-5-one（IX）and N,N’-dinitro-4,4’-azo-bis（1,2,4-triazol-5-one）（XI）were at the range of 144.14-374.35 kJ·mol^-1,and the BDEs of the weakest bond C–NO₂ for compound3-nitro-4-amino-1,2,4-triazol-5-one（IV）and 3,3’-dinitro-4,4’-azo-bis（1,2,4-triazol-5-one）（XII）were at the range of 352.40-376.98 kJ·mol^-1.Natural bond orbital（NBO）,molecular electrostatic potential（MESP）,band gap（ΔE）results of triazlone derivatives showed that the nucleophilic reagent were vulnerable to attack in the ring of 1,2,4-triazolone,and the atoms of N（1）and N（4）in the ring of 1,2,4-triazolone were involved in the formation of a conjugate system.The bond of N–NO₂ introduced in the position of N（1）improved the heat of formation for nitro-triazolone derivatives,and the introduction of azo groups significantly improved theheat of formation for nitro-triazolone derivatives.The calculated detonation velocities of compounds V,VII,VIII,XIII were 9.11,9.20,9.24,9.01 km·s^-1,and the detonation pressures were 37.4,39.12,39.56,and 37.07 GPa,respectively,which were closed to the experimental values of HMX.The calculated detonation velocities ofcompounds IX and XI were 8.85,8.87,and 8.73 km·s^-1,respectively,as well as the detonation pressures were 37.0,33.6,34.7 GPa,respectively,which were closed to the experimental values of RDX.The N–H bonds of TO,ATO,and NTO molecules were hardly nitrified,because the charge density of the N atoms on the N–H structure in the ring of TO,ATO,and NTO were reduced,and a conjugate ring of enol structure was formed by the interaction between the bond of C=O and the ortho bond of N–H.N（4）–NH₂ bond in ATO molecule,as a weakly alkaline,was easily broken in HNO₃ system.So the products obtained by the nitration reaction for TO,NTO and ATO in different nitrating agent.The N（4）–NH₂ bond of ATO was not able to oxidize to be form the N（4）–NO₂ bond by the mixture of H₂SO₄/H₂O₂,and the final product was also NTO.N-（1-acetyl-5-oxo-1H-1,2,4-triazol-4（5H）-yl）acetamide（DAcATO）was obtained by acetylation of N–NH₂ in the ring of ATO,and the single crystal X-ray measurements indicated that the DAcATO crystals appeared as a monoclinic system with space group P2₁/n.The products obtained by the nitration reaction of DAcATO in different nitrating agent were also proved to be NTO.4,4’-Azo-bis（1,2,4-triazolone）（ZTO）based salts from alkaline（Li⁺,K⁺,Na⁺,and Cs⁺）,alkaline earth metal salts(Mg²⁺,Ca²⁺,Sr²⁺,and Ba²⁺)and hydrazinium（N₂H₅⁺）salt were synthesized in a simple,straightforward manner and were characterized by IR and NMR spectroscopy,elemental analysis.The single-crystal X-ray diffraction of seven salts(Na⁺,K⁺,Cs⁺,Mg²⁺,Ca²⁺,Sr²⁺,Ba²⁺,and N₂H₅⁺)showed that in the title compounds,the metal atoms were bonded to the nitrogen and oxygen atoms in the bistetrazole ring to form a sandwich structure.The thermal stabilities of all the title compounds were determined using TG-DTA,and the impact sensitivities of those were tested with a fall hammer apparatus.All these new materials exhibited excellent thermal stability,high density,acceptable detonation properties,and excellent insensitivity to impact(h₅₀≥60 cm).In particular,the CsZTO·H₂O（4）,SrZTO·4H₂O（8）and BaZTO·4H₂O（9）salts are of great interest as potential insensitive energetic materials.N,N′-Diacetyl-4,4′-azo-bis（1,2,4-triazolone）（DAcZTO）and N,N′-Dinitro-4,4′-azo-bis（1,2,4-triazolone）（DNZTO）were two novel N,N′-azo azole poly-nitrogen compound with N₄ structure.The crystal structures showed a delocalization of the azoπbond along the N₄ moiety within the molecules of DAcZTO and DNZTO,which may also accounted for the remarkable stability of this type of compound.Thanks to many C–H,C=O,and N–N bonds that exist in the structure of DAcZTO,many moderate insensitive hydrogen bond of C–H…O（the bond length is 2.32–2.60?and the angle is 117–169°）play an important role in the stability of DAcZTO.The crystal structure of DNZTO·CH₃CN appeared as a monoclinic system with space group P2₁/n.There was no obvious hydrogen bond interaction between the molecules.DSC results showed that a single sharp exothermic decomposition occurred at 282.4,250.8 and 156.4℃at heating rates of 2℃·min^-1 during the thermal decomposition of ZTO,DAcZTO and DNZTO,respectively.There were one endothermic peak and one exothermic peak located at 144.0 and 266.6℃during the thermal decomposition of N₂H₅ZTO,respectively.Under non-isothermal conditions,the apparent activation energies（E_a）of ZTO,DAcZTO,N₂H₅ZTO,and DNZTO were 261.6,302.5,252.6,and 148.0kJ·mol^-1,respectively,and the pre-exponential factor（A）of those were 1.552×10²²,1.395×10²⁸,1.632×10²²,and 3.81×10¹⁵ s^-1,respectively.The critical temperatures of thermalexplosion（T_b）of were 268.6,245.2,265.1,and 125.2℃,respectively.FTIR-TGA-MS results showed that ZTO and DNZTO pyrolysis into gas at 283 and 152℃,respectively,and the gas product was mainly made up of CO₂,CO,NO₂,NO,HCN and N₂.The TGA results showed that at 165℃,N₂H₅ZTO salt and then the ZTO^-ligand accelerated to decompose with the increase of temperature,as well as the gas product of was mainly made up of CO₂,NO₂,HCN and N₂.Accelerating Rate Calorimetry（ARC）results showed that the onset decomposition temperatures（T_o）of ZTO,N₂H₅ZTO,and DNZTO were 203.6,105.7 and 116.7℃,respectively;the adiabatic rising temperatures(ΔT_ad)of those were 25.5,17.7,and 13.1℃,respectively;the max temperature rate（β_T）were 105.6,0.08,and 0.47℃·min^-1,as well as their self-accelerating times were 238.5,260.0,and 49.0 min,respectively.Time to maximum rate（TMR）and self-accelerating decomposition temperature(T_D24)of DNZTO were 1.01 minand 109.8℃,respectively.Under adiabatic condition,the E_a of ZTO,N₂H₅ZTO,and DNZTO were 933.1,215.9,and283.1 kJ·mol^–1,and the A of those were 1.326×10⁹²,1.181×10²⁵,and 9.915×10³³ s^-1,respectively,suggesting that DNZTO composition was vulnerable to thermal hazard.