Abstract
After concerns regarding the use of chlorinated material for pyrotechnic items had reinforced, the action of the U.S. Environmental Protection Agency on health concerns about strontium ushered in a new era in the production of red light. Lithium was shown to impart red color to a pyrotechnic flame, however only a very narrow selection of such formulations can be found in the literature. Dihydrobis(azolyl)borates are a well investigated, easily accessible class of materials which have been proven to be suitable as pyrotechnic coloring agents. With their high nitrogen contents such moieties should also meet the requirements of a low combustion temperature and a reducing flame atmosphere for a lithium‐based red‐burning composition. This work evaluates the capability of the lithium salts of dihydrobis(pyrazol‐1‐yl)borate, dihydrobis(1,2,4‐triazol‐1‐yl)borate, and dihydrobis(tetrazol‐1‐yl)borate to serve as red color imparters. The latter compounds were characterized by multinuclear NMR experiments, IR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction and were investigated with respect to their thermal stabilities as well as sensitivities toward various ignition stimuli.
Highlights
The findings that the perchlorate anion impedes the iodide uptake into the thyroid gland[1] and that organochlorine compounds combust to highly carcinogenic polychlorinated aromatics[2] were followed by a reduction of the advised strontium level in drinking water by the U.S Environmental Protection Agency due to its impact on skeletal development.[3]. These events have recently motivated pyrotechnicians to break with the long-standing tradition of generating the metastable red light-emitting species strontium(I) chloride in a pyrotechnic flame by mixing strontium nitrate with a metallic fuel, poly(vinyl chloride) and potassium perchlorate as an additional chlorine donor.[4]
The formation of the metastable green light-emitting species boron dioxide[12] should require an excess of oxygen in the flame so that the red color impression provoked by a lithium dihydrobis(azolyl)borate is expected to be predominant
Three new lithium dihydrobis(azolyl)borate salts carrying 1H-pyrazole, 1H-1,2,4-triazole or 1H-tetrazole as ligands were synthesized in satisfactory yields via the Lewis acid-base reactions between borohydrides and the respective heterocycles
Summary
The findings that the perchlorate anion impedes the iodide uptake into the thyroid gland[1] and that organochlorine compounds combust to highly carcinogenic polychlorinated aromatics[2] were followed by a reduction of the advised strontium level in drinking water by the U.S Environmental Protection Agency due to its impact on skeletal development.[3]. Dihydrobis(azolyl)borates have been intensively studied over the past 50 years,[10] are accessible by only one reaction step and have even been reported to be suitable coloring agents for green-burning pyrotechnic items.[10c] Such salts and Li2ANAT have in common that both have high nitrogen contents to create a reductive flame atmosphere and to cool the flame.[11] The formation of the metastable green light-emitting species boron dioxide[12] should require an excess of oxygen in the flame so that the red color impression provoked by a lithium dihydrobis(azolyl)borate is expected to be predominant.
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