[(3-Nitro-1H-1,2,4-triazol-1-yl)-NNO-azoxy]furazans: energetic materials containing an N(O)N–N fragment†
The strategy for the synthesis of substituted [(3-nitro-1H-1,2,4-triazol-1-yl)-NNO-azoxy]furazans 4–7, in which the distal nitrogen of the azoxy group is bonded to the nitrogen atom of the azole ring, includes, firstly, the reaction of 1-amino-3-nitro-1H-1,2,4-triazole with 2,2,2-trifluoro-N-(4-nitrosofurazan-3-yl)acetamide in the presence of dibromisocyanuric acid followed by removing of the trifluoroacetyl protecting group to afford aminofurazan (4). Transformation of the amino group in the latter made it possible to synthesize the corresponding nitro (5), azo (6), and methylene dinitramine (7) substituted furazans. The compounds synthesized are thermally stable (decomposition onset temperatures 147–228 °C), exhibit acceptable densities (1.77–1.80 g cm−3) and optimal oxygen balance (the oxidizer excess coefficients α = 0.42–0.71). Their standard enthalpies of formation (576–747 kcal kg−1) were determined experimentally by combustion calorimetry and these compounds have been estimated as potential components of solid composite propellants. In terms of the specific impulse level, model solid composite propellant formulations based on nitro and methylene dinitramine substituted furazans 5 and 7 outperform similar formulations based on CL-20 by 1–4 s, and formulations based on HMX and RDX by 5–8 s.