Energetic N,N′-Ethylene-Bridged Bis(nitropyrazoles): Diversified Functionalities and Properties

A new class of N,N′-ethylene-bridged bis(nitropyrazoles) was synthesized and fully characterized. The highly efficient formation of the N,N′-ethylene bridge was accomplished using dibromoethane and ammonium or potassium pyrazolate. Further functional-group transformations of diaminobis(pyrazole) and dichlorobis(pyrazole) gave rise to diversified derivatives, including dinitramino-, diazido- and hexanitrobis(pyrazole). Single-crystal X-ray diffractions were obtained for hexanitro and diazido derivatives to illustrate the structural characteristics. Heats of formation and detonation performance were calculated by using Gaussian 03 and EXPLO5 v6.01 programs, respectively. Because of the different functionalized groups, the impact and friction sensitivities of these new compounds range from insensitive to sensitive. Among them, the hexanitro derivative displays the most promising overall energetic properties (density (ρ)=1.84 g cm^-3; decomposition temperature (T_d)=250 'C; detonation pressure (P)=34.1 GPa; detonation velocity (v_D)=8759 m s^-1; impact sensitivity (IS)=25 J; friction sensitivity (FS)=160 N), which is competitive with those of 1,3,5-trinitrotriazacyclohexane (ρ=1.80 g cm^-3; T_d=205 'C; P=35.0 GPa; v_D=8762 m s^-1; IS=7 J; FS=120 N).