Thermal Decomposition and Hypergolic Reaction of a Dicyanoborohydride Ionic Liquid

Abstract

In this study, in situ infrared spectroscopy techniques and thermogravimetric analysis coupled with mass spectrometry (TGA−MS) are employed to characterize the reactivity of the ionic liquid, 1-butyl-3-methylimidazolium dicyanoborohydride (BMIM + DCBH − ), in comparison to the well-characterized 1-butyl-3-methylimidazolium dicyanamide (BMIM + DCA − ) ionic liquid. TGA measurements determined the enthalpy of vaporization (ΔH vap ) to be 112.7 ± 12.3 kJ/mol at 298 K. A rapid scan Fourier transform infrared spectrometer was used to obtain vibrational information useful in tracking the appearance and disappearance of species in the hypergolic reactions of BMIM + DCBH − and BMIM + DCA − with white fuming nitric acid (WFNA) and in the thermal decomposition of these energetic ionic liquids. Attenuated total reflectance measurements recorded the infrared spectra of the reactant sample (BMIM + DCBH − ) and the liquid reaction products after reacting with WFNA. Computational chemistry efforts, aided by the experimental results, were used to propose key reaction pathways leading to the hypergolic ignition of BMIM + DCBH − + WFNA. Experimental results indicate that the hypergolic reaction of BMIM + DCBH − with WFNA generates both common and unique intermediates as compared to previous BMIM + DCA − + WFNA investigations: nitrous oxide was generated during both hypergolic reactions indicating that it may play a crucial role in the hypergolic ignition process, NO 2 was generated in significantly higher concentrations for BMIM + DCBH − than for BMIM + DCA − , CO 2 was only generated for BMIM + DCA − , and HCN was only generated during thermal decomposition and hypergolic ignition of BMIM + DCBH − .

Molecular Dynamics Simulations and Product Vibrational Spectral Analysis for the Reactions of NO2 with 1-Ethyl-3-methylimidazolium Dicyanamide (EMIM+DCA–), 1-Butyl-3-methylimidazolium Dicyanamide (BMIM+DCA–), and 1-Allyl-3-methylimidazolium Dicyanamide (AMIM+DCA–)

“…55 However, NO 2 is indeed produced in the hypergolic reactions via the thermal decomposition of HNO 3 . 56 In this context, the work on the NO 2 oxidation of dialkylimidazolium− DCA ILs provides insights into the IL oxidation and combustion chemistry that occur at high temperatures.…”

“…In fact, the addition of N 2 O 4 /NO 2 has made the ignition delay time longer in the hypergolic reaction of BMIM + DCA – with HNO 3 . However, NO 2 is indeed produced in the hypergolic reactions via the thermal decomposition of HNO 3 . In this context, the work on the NO 2 oxidation of dialkylimidazolium–DCA ILs provides insights into the IL oxidation and combustion chemistry that occur at high temperatures.…”

Molecular Dynamics Simulations, Reaction Pathway and Mechanism Dissection, and Kinetics Modeling of the Nitric Acid Oxidation of Dicyanamide and Dicyanoborohydride Anions

“…, HNCO, N 2 O, and NO 2 ) could be produced by the thermal decomposition of its preignition product O 2 N–NHC­(O)­NCN – and/or DNB – . Herein, we focus on comparing the theoretical oxidation products of DCBH – (identified in the trajectories and/or inferred from the reaction coordinates) with the TGA–MS and infrared spectroscopic measurements of the thermal decomposition and hypergolic reaction of BMIM + DCBH – …”

“…Recently, Thomas et al compared the hypergolic reactions of BMIM + DCA – and BMIM + DCBH – with WFNA . The two ILs generated both common and unique products.…”

The Electrolysis of Ammonium Dinitramide in Dimethyl Sulfoxide

“…The discovery of IL hypergols , which ignite instantly upon contact with an appropriate oxidizer, has also opened up a new research avenue related to bipropellant applications. Thus, the exploration of high‐performance hypergolic EILPs has become of interest in the field of IL chemistry, and there have been numerous studies related to new hypergolic EILPs and their hypergolic mechanisms .…”