The assembly of nitrogen-rich building blocks determines the energy storage capacity and affects the stability of energetic materials. Owing to the environmentally harmful properties of the propellant, ammonium perchlorate (AP), much research has explored halogen-free replacements which often suffer from poor thermal stability. In our goal of balancing performance and stability, we report access to an energetic molecule (3) by smart assembly of an azo bridge into trinitromethyl triazoles. Compound 3 exhibits a decomposition temperature of 175 °C, which approaches the highest among reported trinitromethyl derivatives. The density (1.91 g cm −3 ) and oxygen balance (+29%) for 3 exceed other candidates, suggesting it as a high energy dense oxidizer (HEDO) replacement for AP in rocket propellants. One-step azo-involved cyclization of 3 give two fused nitro triazolones, (FNTO) 4 and its N -oxide 5, having thermal stabilities and energies superior to the analogous derivatives of 5-nitro-2,4-dihydro-3 H -1,2,4-triazole-3-one (NTO). The comparison of properties of the fused triazolones 4 and 8 and their N -oxide derivatives 5 and 9 shows that formation of an N -oxide is an effective strategy which results in an increase of the decomposition temperature, oxygen balance, specific impulse, and detonation properties and in a decrease of the sensitivity of the corresponding energetic material. This work highlights bridged and fused triazolic energetic frameworks with an azo building block providing an alternative structural motif for seeking an applicable high-energy ingredient. 
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                            Very thermostable energetic materials based on a fused-triazole: 3,6-diamino-1 H -[1,2,4]triazolo[4,3- b ][1,2,4]triazole
                        
                    
    
            3,6-Diamino-1 H -[1,2,4]triazolo[4,3- b ][1,2,4]triazole ( 1 ) and its energetic salts ( 2–9 ) were designed and synthesized based on a fused-triazole backbone with two C-amino groups as substituents. Their physicochemical and energetic properties were measured or calculated. Among them, compound 1 exhibits superior thermostability ( T d (onset) : 261 °C), surpassing its analogues 3,7-diamino-7 H -[1,2,4]triazolo[4,3- b ][1,2,4]triazole (DATT, 219 °C) and 3,6,7-triamino-7 H -[1,2,4]triazolo[4,3- b ][1,2,4]triazole (TATOT, 245 °C). The differences in thermal stabilities were further investigated by determining the lowest bond dissociation energies (BDE) where a positive correlation between the stability of the molecules and the lowest BDE values is observed. The results show that 1 with the highest value for the lowest BDE has a superior thermostability in comparison to DATT and TATOT. The energetic salts ( 2–9 ) also exhibit remarkable thermal stabilities as well as low impact and friction sensitivities. The fused-triazole backbone 1 H -[1,2,4]triazolo[4,3- b ][1,2,4]triazole with two C-amino groups as substituents is shown to be a promising building block for construction of very thermally stable energetic materials. 
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                            - Award ID(s):
- 1919565
- PAR ID:
- 10250551
- Date Published:
- Journal Name:
- New Journal of Chemistry
- Volume:
- 45
- Issue:
- 1
- ISSN:
- 1144-0546
- Page Range / eLocation ID:
- 85 to 91
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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