Oxidation of a Levitated Droplet of 1-Allyl-3-methylimidazolium Dicyanamide by Nitrogen Dioxide

Abstract

Understanding the reaction mechanisms of ionic liquids and their oxidizers is necessary to develop the next generation of hypergolic, ionic-liquid-based fuels. We studied reactions between a levitated droplet of 1-allyl-3-methylimidazolium dicyanamide ([AMIM]­[DCA]), with and without hydrogen-capped boron nanoparticles, and nitrogen dioxide (NO2). The reactions were monitored with Fourier-transform infrared (FTIR) and Raman spectroscopy. The emergence of new structures in the FTIR and Raman spectra is consistent with the formation of functional groups including organic nitrites (RONO), nitroamines (R1R2NNO2), and carbonitrates (R1R2C=NO2 –). Possible reaction mechanisms based on these new functional groups are discussed. The reaction rates were deduced at various temperatures by heating the levitated droplets with a carbon dioxide laser. We thereby determined an overall activation energy of 38.5 ± 2.3 kJ mol–1 for the oxidation of [AMIM]­[DCA] for the first time.

Oxidation of a Levitated 1-Butyl-3-methylimidazolium Dicyanoborate Droplet by Nitrogen Dioxide

“…This is consistent with our previous work on the oxidation of ionic liquids with NO 2 . 28,29,54 The oxidations of ionic liquids are very complex systems, so further reactions may occur. 54 The nitrogen dioxide was found to react significantly with both the [DCBH] − or [DCA] − anions.…”

“…28,29,54 The oxidations of ionic liquids are very complex systems, so further reactions may occur. 54 The nitrogen dioxide was found to react significantly with both the [DCBH] − or [DCA] − anions. For all four ionic liquids, the new peaks are consistent with the formation of functional groups of organic nitro-compounds, but only [BMIM][DCBH] formed structure produced by boron-containing compounds as expected.…”

“…There also appears to be a difference in the oxidation of the boron when incorporated into the anion or added to the ionic liquid in the form of nanoparticles, as in the previous studies. 28,29,54 The vibrational spectra of [BMIM][DCBH] after oxidation showed evidence for oxidized boron such as the B−N and B−O vibrational modes. In contrast, the IL-capped boron nanoparticles produced only minor effects on the vibrational spectra of the [DCA] − -containing ILs, implying that the IL capping limited the oxidation of the nanoparticles.…”

“…In contrast, the IL-capped boron nanoparticles produced only minor effects on the vibrational spectra of the [DCA] − -containing ILs, implying that the IL capping limited the oxidation of the nanoparticles. 28,29,54 ■ ASSOCIATED CONTENT * S Supporting Information…”

“…Key: v, stretching; s, symmetric; as, antisymmetric. The Journal of Physical Chemistry A i v i d u a l n o t d i r e c t l y a s s o c i a t e d w i t h s c i t e i s p r o h i b i t e d .cm −1 region could be caused by dinitrogen tetroxide (N 2 O 4 ) dissolved in the droplet 28,29,54. More specifically, the v 5 and v 9 vibrational modes of N 2 O 4 occur at 1718 and 1735 cm −1 and thus could account for the peak at 1733 cm −1 .55 Our previous studies on the [DCA] − -based ionic liquids revealed multiple resolved peaks in the 1700−1800 cm −1 wavenumber region that were assigned to the C=O functional group or N 2 O 4 vibrational modes; therefore, the unresolved structure here is likely a combination of the same modes 28,29,54.…”