Synthesis and performance study of methylene-bridged bis(nitramino-1,2,4-oxadiazole) and its energetic salts

In this work, a series of new compounds, 2–9, was synthesized through a simple, safe and efficient route. Dihydroxyimino-malonic acid diamide was chosen as the starting material to react with trichloroacetic anhydride to form 1,2,4-oxadiazole rings. Then, the products from the ring-forming reaction were reacted with an excess amount of ammonia in methanol to give 3,3′-methylenebis(1,2,4-oxadiazol-5-amine) (2). Further nitration of compound 2 gave N,N′-(methylenebis(1,2,4-oxadiazole-3,5-diyl))dinitramide (3, DNAMBO). A series of DNAMBO-based energetic salts, 4–9, paired with nitrogen-rich cations was readily obtained by treating compound 3 with two equivalents of free base. The physicochemical and energetic properties of compounds 3–9, including density, thermal stability, and sensitivity, were investigated, and the detonation performances were calculated by using the Kamlet–Jacobs equations. Among them, the hydrazinium salt (5) shows the best detonation performance (5: d = 1.69 g cm−3; Td = 147.5 °C; P = 27.1 GPa; vD = 7962 m s−1).