Hypergolicity of Cyanoborohydride Ionic Liquids with H ₂ O ₂ and HNO ₃ as Oxidizers in the Liquid Phase

Ab initio molecular dynamics simulations were performed to investigate the reaction mechanisms and kinetics of the ionic liquid 1-ethyl-3-methylimidazolium cyanoborohydride ([EMIM]⁺[CBH]⁻) with two oxidizers, hydrogen peroxide (H₂O₂) and nitric acid (HNO₃), in liquid phases. Neither of the systems is unstable enough to react within the time frame of unbiased simulations; thus, well-tempered metadynamics was employed to accelerate reactions along selected collective variables (CVs). A large number of CVs were screened, and the CVs corresponding to the lowest bias energy were chosen. The required bias energy for oxidation of the [EMIM]⁺[CBH]⁻/H₂O₂ system was found to be about half of what is required for [EMIM]⁺[CBH]⁻/HNO₃. Reaction rate constants estimated using infrequent metadynamics indicate that the oxidation with H₂O₂ is about 10¹⁰ times faster than that with HNO₃. Both results agree with the levitated droplet merging experiments, which showed that rock-grade H₂O₂ is a much more efficient oxidizer. Analysis of the trajectories reveals an extensive rearrangement of the hydrogen bond network in the H₂O₂ system.