Comparison of Functionalized Lithium Dihydrobis(azolyl)borates with Their Corresponding Azolates as Environmentally Friendly Red Pyrotechnic Coloring Agents

Abstract

The recent awareness of the impact of strontium on health has stimulated research efforts on lithium-based red pyrotechnic colorants. We have previously shown lithium dihydrobis(azolyl) borates to be promising candidates due to their favorable adjustment to a reductive and low-temperature flame atmosphere. These compounds are assumed to be sufficiently stable only if the pK a values of the heterocycles are between 5 and 20. Apart from their acidities, functionalization of 1H-tetrazole and 1H-pyrazole with nitro or amino groups, respectively, tailors the oxygen balances of the resulting Lewis acid base adducts to enhance the fuel-rich flame environment or to make them oxidizing agents. This work determines whether the lithium salts of dihydrobis(3-nitropyrazol-1-yl)borate and dihydrobis(5aminotetrazol-1-yl)borate are suitable replacements for strontium-containing color imparters. Furthermore, the influence of potentially green-light-producing boron is evaluated by comparing the emissions of the lithium borates and the corresponding lithium azolates.

Lithium Nitropyrazolates as Potential Red Pyrotechnic Colorants

“…[23] Although a lot of effort has been put into finding synthesis strategies circumventing the unstable intermediate 1 N-nitropyrazole (1) and into establishing milder and more environmentally benign nitration systems, [27] the conventional method has been studied more comprehensively. [23,26] When 1 was rearranged according to our optimized procedure, [28] we did not encounter any problems concerning the isolation of the desired product, but with that of 1,3-dinitropyrazole (4). Commonly, after thermolysis 5 is separated from 3-nitro-1H-pyrazole (2) impurities by precipitation of a corresponding salt and subsequent neutralization [5,29] or by recrystallization from benzene.…”

A review of colored light production by pyrotechnic materials

“…In another study [47c], Klapötke and co‐workers examined salts of lithium dihydrobis(azolyl)borates with 5‐aminotetrazole or 3‐nitropyrazole as ligands as well as their corresponding azolates. The synthesis of potassium dihydrobis(3‐nitropyrazol‐1‐yl)borate was improved in terms of safety and yield.…”