Finding furoxan rings

A furoxan ring is derived from a dinitromethyl group. A plausible mechanism is proposed based on ¹H, ¹³C and ¹⁵N NMR spectral analysis where a dinitromethyl group releases one molecule of nitric acid to form an unstable nitrile oxide and its dipole isomer which cyclize to a furoxan ring [3,4-bis(4-nitro-1,2,5-oxadizaol-3-yl)-1,2,5-oxadiazole-N-oxide (5)]. This new method of constructing a furoxan (1,2,5-oxadiazole 2-oxide) ring offers a potentially efficient way to obtain excellent energetic materials. In order to stabilize the dinitromethyl-containing precursor [3-(dinitromethyl)-4-nitro-1,2,5-oxadiazole (4)], a series of new energetic salts was synthesized and fully characterized. These materials exhibit high densities, excellent detonation properties and acceptable sensitivities. For example, the hydrazinium salt 9 has a high density of 1.92 g cm^-3, a detonation velocity of 9437 m s^-1 and a detonation pressure of 41.3 GPa, which approach those properties of CL-20 (ρ, 2.03 g cm^-3; v_D, 9406 m s^-1; P, 44.6 GPa) and which are superior to those of HMX (ρ, 1.90 g cm^-3; v_D, 9320 m s^-1; P, 39.2 GPa).