Synthesis and Properties of 4,4',5,5'-Tetranitro-1H,1'H-2,2'-Biimidazole Salts: Semicarbazidium, 3-Amino-1,2,4-Triazolium, and 5-Aminotetrazolium Derivatives

Ionic derivatives of 4,4',5,5'-tetranitro-1 H ,1' H -2,2'-biimidazole have recently been identified as interesting low-sensitivity explosive compounds that combine low vulnerability to mechanical stimuli with high performance. In this work, the synthesis of bis-semicarbazidium), bis(3-amino-1 H -1,2,4-triazol-4-ium), and bis(5-amino-4 H -tetrazol-1-ium) 4,4',5,5'-tetranitro-2,2'-biimidazol-1-ides is described, and some of their experimental and calculated explosive properties are presented. 4,4',5,5'-Tetranitro-1 H ,1' H -2,2'-biimidazole was synthesized by nitration of 2,2'-biimidazole with nitric acid in polyphosphoric acid and produced the salts in good yields and purity by reaction with semicarbazide hydrochloride in water, 3-amino-1,2,4-triazole in methanol, and 5-aminotetrazole in diethyl ether. The obtained salts were characterized by NMR and infrared spectroscopy, elemental analysis, thermal analysis, and small-scale safety testing impact and friction sensitivity). The measured densities and standard enthalpy of formation, as well as calculated performance characteristics are reported. The compounds are thermally stable up to 180–210°C and insensitive to mechanical stimuli and have slightly better performance than trinitrotoluene with regard to calculated detonation parameters.