Synthesis and properties of 4,4’,5,5’-tetranitro-2,2’-biimidazolates: bis-semicarbazidium, bis(3-amino-1,2,4-triazolium) and bis(5-aminotetrazolium)
Ionic derivatives of 4,4’,5,5’-tetranitro-2,2’-biimidazole (TNBI) have recently been identified as interesting low sensitivity explosive compounds that combine low vulnerability to mechanical stimuli with high performance. In this work bis-semicarbazidium (1), bis(3- amino-1,2,4-triazolium) (2), bis(5-aminotetrazolium) (3) 4,4’,5,5’-tetranitro-2,2’-biimidazolates were synthesized and some of their experimental and calculated explosive properties are presented. TNBI was synthesized by nitration of 2,2’-biimidazole (BI) with nitric acid in polyphosphoric acid. Salts 1, 2, and 3 can be easily prepared in good yields and purity by reaction of TNBI with semicarbazide hydrochloride in water, 3-amino-1,2,4-triazole in methanol, and 5-aminotetrazole in diethyl ether, respectively. The compounds were characterized by NMR and vibrational spectroscopy, elemental analysis, thermal analysis (DSC, DTA/TG), 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. The TNBI salts have slightly better performance than TNT with regard to calculated detonation parameters.