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Hypergolic ionic liquids: to be or not to be?

Souvick BiswasKazuumi FujiokaIvan AntonovGrace L RizzoSteven D ChambreauStefan SchneiderRui SunRalf I Kaiser
Published in: Chemical science (2023)
Hypergolic ionic liquids (HIL) - ionic liquids which ignite spontaneously upon contact with an oxidizer - emerged as green space propellants. Exploiting the previously marked hypergolic [EMIM][CBH] - WFNA (1-ethyl-3-methylimidazolium cyanoborohydride - white fuming nitric acid) system as a benchmark, through the utilization of a novel chirped-pulse droplet-merging technique in an ultrasonic levitation environment and electronic structure calculations, this work deeply questions the hypergolicity of the [EMIM][CBH]-WFNA system. Molecular oxygen is critically required for the [EMIM][CBH]-WFNA system to ignite spontaneously. State-of-the-art electronic structure calculations identified the resonantly stabilized N -boryl- N -oxo-formamide [(H 3 B-N(O)-CHO) - ; BOFA] radical anion as the key intermediate in driving the oxidation chemistry upon reaction with molecular oxygen of the ionic liquid. These findings challenge conventional wisdom of 'well-established' test protocols as indicators of the hypergolicity of ionic liquids thus necessitating truly oxygen-free experimental conditions to define the ignition delay upon mixing of the ionic liquid and the oxidizer and hence designating an ionic liquid as truly hypergolic at the molecular level.
Keyphrases
  • ionic liquid
  • room temperature
  • molecular dynamics
  • density functional theory
  • molecular dynamics simulations
  • single molecule
  • single cell
  • nitric oxide
  • electron transfer