Pushing the Energy-Sensitivity Balance with High-Performance Bifuroxans
Several energy-rich bifuroxans incorporating nitro and azido functionalities have been synthesized and thoroughly characterized by IR and multinuclear NMR spectroscopy, elemental analyses, single-crystal X-ray diffraction, and differential scanning calorimetry. N-oxide regiochemistry was employed to design the tunable azido(nitro)bifuroxans with different physicochemical and energetic properties. All synthesized compounds have high enthalpies of formation (449-777 kJ mol(-1)) and attractive performances, as evidenced by the high detonation velocities (8.95-9.75 km s(-1)) and Champan-Jouguet pressures (35-45 GPa). The most powerful energetic material in this series is 4,4'-dinitro-3,3'-bifuroxan. This hydrogen-free molecule (C4N6O8) exhibits an outstanding heat of explosion value of 15.3 kJ cm(-1), far exceeding the top energetic material hexanitrohexaazaisowurtzitane CL-20. At the same time, the impact and friction sensitivities of 4,4'-dinitro-3,3'-bifuroxan were deemed acceptable for practical use. Overall, 4,4'-dinitro-3,3'-bifuroxan breaks a general trend called the "energy-sensitivity rule", which describes a linear increase of the mechanical sensitivity with a growth of the energetic content of the molecule, and, thus, offers great promise for future applications.