Pushing the Limits of Oxygen Balance in 1,3,4-Oxadiazoles

Gem-trinitromethyl groups were introduced into a 1,3,4-oxadiazole ring to give the first example of a bifunctionalized single five-membered ring with six nitro groups. 2,5-Bis(trinitromethyl)-1,3,4-oxadiazole (12) has a high calculated crystal density of 2.007 g cm^-3 at 150 K (1.941 g cm^-3 at 293 K) and a very high positive oxygen balance (39.12%), which makes it a strong candidate as a high energy dense oxidizer. The dihydroxylammonium and dihydrazinium salts of bis(trinitromethyl)-1,3,4-oxadiazole (5 and 6) exhibit excellent calculated detonation properties (5, v_D = 9266 m s^-1, P = 38.9 GPa; 6, v_D = 8900 m s^-1, P = 36.3 GPa) and acceptable impact sensitivities (5 20 J, 6 19 J), which are superior to those of RDX (7.4 J) and HMX (7.4 J). Such attractive features support the application potential of the gem-polynitromethyl group in the design of advanced energetic materials. Surprisingly, 2,5-bis(trinitromethyl)-1,3,4-oxadiazole (12) is more thermally stable and less sensitive than its bis(dinitromethyl) analogue, 8.