Lithium dihydrobis(azolyl)borates as colorants for strontium- and chlorine-free red pyrotechnics

摘要

In 2014, the U.S. Environmental Protection Agency declared strontium to be harmful to health based on findings of its adverse effect on the human bone strength with calcium deficiency and during skeletal development. When this contaminant was determined to be present in 99 % of all public water systems in the U.S. and in 7 % out of these even at levels of concern, the EPA was considering to regulate the amount of strontium in drinking water. While the potential carcinogenicity of polychlorinated aromatics, released during the combustion of chlorinated material, had long been known at this point, this recent progress again revolutionized the way of producing red light in pyrotechnics. This work approaches the current issue of banning both chlorine and strontium from pyrotechnic formulations by proposing lithium dihydrobis(azolyl)borate salts as alternative colorants which generate metastable atomic lithium as the red light-emitting species in the flame. Such moieties should not only be environmentally benign in terms of their emitter but also in regard of their combustion products. The driving force for an efficient burn-down is the formation of molecular nitrogen and diboron trioxide. Detailed information are given on the synthesis of the lithium salts of dihydrobis(pyrazolyl)borate, dihydrobis(1,2,4-triazolyl)borate and dihydrobis(tetrazolyl)borate as well as on the analytics and on their optical performance in pyrotechnic compositions.