Construction of 3-Nitro-1H-pyrazole-5-yl-Bridged/Fused 4,5-Diamino-4H-1,2,4-triazoles Achieving High-Energy Insensitive Energetic Materials.

Abstract

Aminotriazole is a privileged structural motif in the design of various thermostable and insensitive energetic materials. A series of 3-nitro-1H-pyrazole-5-yl-bridged/fused 4,5-diamino-4H-1,2,4-triazoles was prepared via the cycloaddition of carboxyl pyrazole as a raw material. These newly synthesized compounds and their corresponding salts were fully characterized by chemical analysis (single-crystal X-ray diffraction, infrared, NMR, and mass spectroscopy) as well as experimental tests (thermostability and sensitivities). Their detonation properties (detonation velocity, detonation pressure, etc.) were determined with the EXPLO5 program on the basis of crystal density and calculated heat of formation with the Gaussian 09 suite. These pyrazole-triazoles show very high thermostabilities (Td > 320 °C) and low mechanical sensitivities (IS ≥ 25 J, FS ≥ 288 N) due to intermolecular hydrogen bonding interactions in polycyclic triazoles. In particular, tricyclic 3a displays an ultrahigh decomposition temperature of 371 °C, surpassing that of 2,2',4,4',6,6'-hexanitrostilbene (HNS) and can be used as a candidate for heat-resistant explosives. Dinitroamino compounds 2 (PCJ = 38.58 GPa, Vdet = 9268 m s-1) and 2d (PCJ = 36.15 GPa, Vdet = 8913 m s-1) were found to show excellent detonation performance, with 2 being comparable to 1,3,4,7-tetranitro-1,3,5,7-tetrazocane (HMX). Furthermore, compound 1 exhibits desirable detonation properties (PCJ = 34.74 GPa, Vdet = 9284 m s-1), high thermostability (333 °C), and low sensitivities (IS > 40 J, FS > 360 N), making it a promising HMX replacement. This study supports the superiority of utilizing the polycyclic pyrazole-triazole system in the development of new high-energy insensitive energetic materials.