Synthesis, characterization, testing, and detonation performance studies of fused pyrazole-based fluorescent energetic materials

Abstract

Experts in the field of high energy materials strive to maintain a fine balance between energy and stability using nitrogen-rich materials and to apply sustainable development principles. Among the heterocyclic backbones, fused moieties are considered a significant backbone in energetic materials owing to their high energy content, dense nature, and stability. We have synthesized pyrazole-based fused compounds with high thermal stability, insensitivity, and moderate detonation performance to contribute to this development. All the compounds were isolated without column chromatography in one or two steps using commercially available affordable starting materials with excellent yields. Their molecular structure, crystallization, physicochemical properties, thermal stability and sensitivity behaviour were evaluated and compared with 2,4,6-trinitrotoluene (TNT), hexanitrostilbene (HNS), and 3,5-dinitro-N,N′-bis(2,4,6-trinitrophenyl) (PYX). All the compounds show acceptable detonation velocities (VOD: 7344–8068 m s−1), pressures (DP: 19–24.5 GPa), and insensitive to impact (25 - > 40 J) and friction (360 N). Among all the compounds, ammonium salt of 4-oxo-3,4-dihydropyrazolo[3,4-d] [1,2,3]triazin-6-ide (6) shows good density (1.77 g cm−3), detonation velocity (8068 m s−1) as well as 4-amino-pyrimidine 5-oxide (13) shows good physicochemical properties (d: 1.85 g cm−3, VOD: 7924 m s−1) Along with excellent insensitivity to impact and friction (35 - > 40 J and >360 N, respectively). These properties suggest that this can be a suitable replacement for benchmark explosives such as TNT, HNS, and PYX. Interestingly 4-amino-2H-pyrazolo[3,4-d]pyrimidine-5-oxide (3) exhibits fluorescence property, which can be used as a potential candidate in energetic filler or the formulations of energetic material for easy detection.