Dynamics Simulations and Statistical Modeling of Thermal Decomposition of 1-Ethyl-3-methylimidazolium Dicyanamide and 1-Ethyl-2,3-dimethylimidazolium Dicyanamide

Li, Jianbo; Chambreau, Steven D.; Vaghjiani, Ghanshyam L.

doi:10.1021/jp5095849

Cited by 18 publications

(27 citation statements)

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“…This pathway is similar to that seen for the first steps in the DCA – and HNO 3 reaction, , and the free energy barrier here (78.7 kJ/mol) is significantly lower than for HNO 3 + DCA – (26.2 kcal/mol = 109.6 kJ/mol) determined previously (M06-2 X /6-311++G(d,p)) . More work is needed to identify the ignition mechanism, and further work including reactive, direct molecular dynamics − is currently being pursued to better understand the hypergolic nature of this borohydride EIL.…”

Section: Resultssupporting

confidence: 79%

Thermal Decomposition and Hypergolic Reaction of a Dicyanoborohydride Ionic Liquid

et al. 2020

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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 − .

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Section: Resultssupporting

confidence: 79%

Thermal Decomposition and Hypergolic Reaction of a Dicyanoborohydride Ionic Liquid

et al. 2020

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“…An earlier computational study using quasi-classical direct dynamics trajectories for 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]) at the B3LYP/6-31+G** level of theory explored decomposition reactions. Transition states and products were determined using DFT for several decomposition reactions.…”

Section: Resultsmentioning

confidence: 99%

Decomposition of Ionic Liquids at Lithium Interfaces. 1. Ab Initio Molecular Dynamics Simulations

et al. 2017

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This work is Part 1 in a two part series that investigates the interfacial decomposition chemistry of [pyr14][TFSI] and [EMIM][BF 4 ] ionic liquids (IL) at Li metal interfaces. Here, the decomposition is probed primarily through ab initio molecular dynamics (AIMD) simulations. For single ion pairs adsorbed on a Li(100) surface, hybrid ion states are found to emerge about the Fermi level. Interestingly, these states have a significant contribution from both ions, which suggests that the cathodic (reductive) stability could in part be governed by the anions. Room temperature AIMD simulations reveal rapid decomposition of the TFSI anion initiated by C−S and/or S−N bond cleavage due to charge transfer from Li to the anion. The unusual phenomenon of reductive decomposition of the anion is supported by recent experimental reports. The reaction products observed included LiF, LiO, Li 2 F, Li 2 O, SO 2 , NSO 2 , NSO 2 CF 3 , etc., which are all in excellent agreement with the XPS results. Initial decomposition reactions for both cations and the BF 4 anion were only observed in high temperature AIMD simulations. For bulk ILs interfaces with a Li(100) surface, interfacial decomposition reactions again result from charge transfer to the IL from the Li surface, in particular, to anions at the interfaces. The initial decomposition event at bulk interfaces is found to vary depending on the interface structure. The extensive computational analyses presented in this work provide valuable insights into the fundamental interfacial chemistry of ILs in contact with Li metal. In Part 2 1 of this series, we consider these results further by systematically examining ion reductive stability, the thermodynamics of decomposition, and kinetic limitations to decomposition using gas phase density functional theory (DFT) computations. Results from these studies can be used for further design of these, or perhaps other, ILs to obtain more stable solid electrolyte interface (SEI) layers to improve cycling in advanced battery chemistries.

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“…Alkyl abstraction only happens with a terminal N but not with the central N of DCA − , presumably because the barrier leading to the formation of a terminally alkylated DCA is lower than that for a centrally alkylated DCA. 30 In a previous work, 8 we simulated thermal decomposition of single EMIM + DCA − at 4000 K using the B3LYP/6-31G(d) level of theory. The results are included in Table 1 for comparison.…”

Section: Reaction Dynamics Reaction Coordinatesmentioning

confidence: 99%

“…1,6 Therefore, understanding IL thermal stabilities, their reaction mechanisms, and pathways leading to ignition and their associated reaction dynamics and reaction kinetics is of utmost importance in predicting the performance of hypergolic ILs and in optimizing the design of propulsion systems that use ILs. We previously reported photoionization mass spectrometric and infrared spectroscopic measurements 7 and molecular dynamics simulations 8 of the thermal decomposition of 1-ethyl-3-methylimidazolium dicyanamide (EMIM + DCA − ) and 1-ethyl-2,3-dimethylimidazolium dicyanamide (EMMIM + DCA − ). The combination of experimental and theoretical approaches allowed us to determine the decomposition products, branching ratios, and underlying reaction kinetics and reaction dynamics of alkylimidazolium−DCA ILs.…”

Section: Introductionmentioning

confidence: 99%

“…A commonly accepted ignition mechanism between hypergolic ILs and an oxidizer involves two stages: a low-temperature preignition stage during which exothermic redox reactions lead to the formation of gaseous transient species and release of heat, followed by a stage in which the system temperature reaches the kindling point of the highly inflammable gaseous species leading to ignition and subsequent combustion to occur. , Therefore, understanding IL thermal stabilities, their reaction mechanisms, and pathways leading to ignition and their associated reaction dynamics and reaction kinetics is of utmost importance in predicting the performance of hypergolic ILs and in optimizing the design of propulsion systems that use ILs. We previously reported photoionization mass spectrometric and infrared spectroscopic measurements and molecular dynamics simulations of the thermal decomposition of 1-ethyl-3-methylimidazolium dicyanamide (EMIM + DCA – ) and 1-ethyl-2,3-dimethylimidazolium dicyanamide (EMMIM + DCA – ). The combination of experimental and theoretical approaches allowed us to determine the decomposition products, branching ratios, and underlying reaction kinetics and reaction dynamics of alkylimidazolium–DCA ILs.…”

Section: Introductionmentioning

confidence: 99%

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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^–)

2020

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Direct dynamics trajectory simulations were carried out for the NO 2 oxidation of 1-ethyl-3-methylimidazolium dicyanamide (EMIM + DCA − ), which were aimed at probing the nature of the primary and secondary reactions in the system. Guided by trajectory results, reaction coordinates and potential energy diagrams were mapped out for NO 2 with EMIM + DCA − , as well as with its analogues 1-butyl-3-methylimidazolium dicyanamide (BMIM + DCA − ) and 1-allyl-3-methylimidazolium dicyanamide (AMIM + DCA − ). Reactions of the dialkylimidazolium− dicyanamide (DCA) ionic liquids (ILs) are all initiated by proton transfer and/or alkyl abstraction between 1,3-dialkylimidazolium cations and DCA − anion, of which two exoergic pathways are particularly relevant to their oxidation activities. One pathway is the transfer of a H β -proton from the ethyl, butyl, or allyl group of the dialkylimidazolium cation to DCA − that results in the concomitant elimination of the corresponding alkyl as a neutral alkene, and the other pathway is the alkyl abstraction by DCA − via a second order nucleophilic substitution (SN 2 ) mechanism. The intra-ion-pair reaction products, including [dialkylimidazolium + − H C2 + ], alkylimidazole, alkene, alkyl-DCA, HDCA, and DCA − , react with NO 2 and favor the formation of nitrite (−ONO) complexes over nitro (−NO 2 ) complexes, albeit the two complex structures have similar formation energies. The exoergic intra-ion-pair reactions in the dialkylimidazolium−DCA ILs account for their significantly higher oxidation activities over the previously reported 1-methyl-4-amino-1,2,4-triazolium dicyanamide [Liu, J.;et al. J. Phys. Chem. B 2019, 123, 2956−2970] and for the relatively higher reactivity of BMIM + DCA − vs AMIM + DCA − as BMIM + has a higher reaction path degeneracy for intra-ion-pair H β -proton transfer and its H β -transfer is more energetically favorable. To validate and directly compare our computational results with spectral measurements in the ILs, infrared and Raman spectra of BMIM + DCA − and AMIM + DCA − and their products with NO 2 were calculated using an ionic liquid solvation model. The simulated spectra reproduced all of the vibrational frequencies detected in the reactions of BMIM + DCA − and AMIM + DCA − IL droplets with NO 2 (as reported by Brotton et al. [

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Dynamics Simulations and Statistical Modeling of Thermal Decomposition of 1-Ethyl-3-methylimidazolium Dicyanamide and 1-Ethyl-2,3-dimethylimidazolium Dicyanamide

Cited by 18 publications

References 48 publications

Thermal Decomposition and Hypergolic Reaction of a Dicyanoborohydride Ionic Liquid

Thermal Decomposition and Hypergolic Reaction of a Dicyanoborohydride Ionic Liquid

Decomposition of Ionic Liquids at Lithium Interfaces. 1. Ab Initio Molecular Dynamics Simulations

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^–)

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Dynamics Simulations and Statistical Modeling of Thermal Decomposition of 1-Ethyl-3-methylimidazolium Dicyanamide and 1-Ethyl-2,3-dimethylimidazolium Dicyanamide

Cited by 18 publications

References 48 publications

Thermal Decomposition and Hypergolic Reaction of a Dicyanoborohydride Ionic Liquid

Thermal Decomposition and Hypergolic Reaction of a Dicyanoborohydride Ionic Liquid

Decomposition of Ionic Liquids at Lithium Interfaces. 1. Ab Initio Molecular Dynamics Simulations

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–)

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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^–)