Energetic Ionic Liquids Research Articles

Energetic ionic liquids as explosives and propellant fuels: a new journey of ionic liquid chemistry.

Energetic ionic liquids as explosives and propellant fuels: a new journey of ionic liquid chemistry.

Recent developments in the field of energetic ionic liquids

Energetic ionic liquids (EILs) are a subset of the rapidly growing field of ionic liquid research.

Nitrogen‐Rich Energetic Ionic Liquids Based on the N,N‐Bis(1H‐tetrazol‐5‐yl)amine Anion – Syntheses, Structures, and Properties

AbstractN,N‐Bis(1H‐tetrazol‐5‐yl)amine anions (HBTA–/BTA2–) were used as suitable nitrogen‐rich components for the construction of energetic ionic liquids. Seven ionic liquids, namely, 1,3‐dimethylimidazolium (1, [C1mim]HBTA), 1‐ethyl‐3‐methylimidazolium (2, [C2mim]HBTA), 1‐butyl‐3‐methylimidazolium (3, [C4mim]HBTA), 1‐hexyl‐3‐methylimidazolium (4, [C6mim]HBTA), 1‐methyl‐3‐octylimidazolium (5, [C8mim]HBTA), and 1,2,3‐trimethylimidazolium (6, [C1mmim]HBTA) cations with the HBTA– anion and di‐1,2,3‐trimethylimidazolium N,N‐bis(1H‐tetrazol‐5‐yl)amine (7, [C1mmim]2BTA), were synthesized. All materials were fully characterized by IR and NMR spectroscopy, elemental analysis, and high‐resolution mass spectrometry. The crystal structures of 1 and 7 were determined by single‐crystal X‐ray diffraction [1: monoclinic, P21/n, a = 14.0653(4) Å, b = 6.9507(2) Å, c = 22.4699(7) Å, β = 93.996(3)°, V = 2191.38(12) Å3, Z = 8, ρ = 1.511 g cm–3; 7: monoclinic, P21/c, a = 17.5869(3) Å, b = 12.8757(2) Å, c = 21.9203(6) Å, β = 125.0580(10)°, V = 4063.15(15) Å3, Z = 8, ρ = 1.221 g cm–3]. The nitrogen contents of 1–7 exceed 40 %, and 1 has the highest value of 61.78 %. The ionic liquids 1–7 are thermally stable to 220 °C, and 2–5 are room‐temperature ionic liquids. The heats of formation of 1–7 obtained by both experimental and theoretical methods are all positive. The ionic liquids 1–7 are insensitive towards impact (>40 J) and friction (>360 N). They can be ignited in air. These new energetic ionic liquids contain only C, H, and N and are of interest as potential propellants with high energy, high thermal stability, low sensitivity to impact and friction, and environmentally friendly decomposition gases.

Energetic Ionic Materials: How Green Are They? A Comparative Life Cycle Assessment Study

Recently, several energetic ionic salts and liquids have been proposed as novel high-energy materials, propellants, and explosives. The life cycle environmental impacts of these new energetic salts have not been previously studied. Environmental impacts arise both from release of these energetic materials themselves as well as from their synthesis. In this work, for the first time, we report the results of cradle-to-gate life cycle environmental impacts of production of energetic ionic salt 1,2,3-triazolium nitrate and compare it with traditional energetic material 2,4,6-trinitrotoluene (TNT). The results indicate that the production processes of ionic salt have a significantly higher environmental footprint than conventional energetic materials. The above result was consistent across all nine impact categories analyzed and can be directly attributed to energy intensive steps needed to prepare the ionic salt and its precursors. The findings suggest that ionic energetic materials have higher environmental ...

Exploring the Structure of Nitrogen-Rich Ionic Liquids and Their Binding to the Surface of Oxide-Free Boron Nanoparticles

The structure of two different energetic ionic liquids and the nature of their binding to elemental boron surfaces were investigated by a combination of X-ray photoelectron spectroscopy, IR spectroscopy, zeta potential measurements, thermogravimetric analysis, and first-principles theory. It was found that both 1-methyl-4-amino-1,2,4-triazolium dicyanamide ([MAT][DCA]) and 1-butyl-3-methylimidazolium dicyanamide ([BMIM][DCA]) ionic liquids bind to boron well enough to resist removal by ultrasonic washing and to protect the boron surface from oxidation during air exposure of the washed powder. The data suggest that both the cation and the anion of the ionic liquids interact with the boron surface; however, for [MAT][DCA], the interaction of the cation appears to dominate, while for [BMIM][DCA] the interaction with the [DCA]− anion dominates. The difference is attributed to the binding of boron to the amino group of [MAT]+, and the amino group also appears to help bind a thicker ionic liquid (IL) capping layer.

A computational approach to design energetic ionic liquids

The present work deals with the theoretical estimation of ion-pair binding energies and the energetic properties of four ion pairs formed by combining the 1-butyl-2,4-dinitro-3-methyl imidazolium ion with nitrate (I), perchlorate (II), dinitramide (III), or 3,5-dinitro-1,2,4-triazolate (IV) anions. The counterpoise-corrected ion-pair binding energies were calculated for each ion pair at the B3LYP/6-311+G(d,p) level of theory. Results show that the cation-anion interaction is strongest for ion pair I and weakest for IV, indicating that the nitrate (I) has a greater tendency to exist as a stable ionic salt whereas the 3,5-dinitro-1,2,4-triazolate (IV) may exist as an ionic liquid. Natural bond orbital (NBO) analysis and electrostatic potential (ESP) mapping revealed that charge transfer occurs in all of the ion pairs, but is greatest (0.25e) for ion pair I and smallest (0.03e) for IV, resulting in ion pair I being the least polarized. A nucleus-independent chemical shift (NICS) study revealed that the aromaticity of the 1-butyl-2,4-dinitro-3-methyl imidazolium ion significantly increases in ion pair IV, indicating that this has the greatest charge delocalization among all of the four ion pairs considered. Studies of thermodynamic and detonation properties showed that ion pair II is the most energetic ion pair in terms of its detonation velocity (D = 7.5 km s(-1)) and detonation pressure (P = 23.1 GPa). It is also envisaged that ion pair IV would exist as an energetic azolium azolate type ionic liquid that could be conveniently used as a secondary explosive characterized by detonation parameters D and P of 6.9 km s(-1) and 19.3 GPa, respectively. These values are comparable to those of conventional explosives such as TNT.

Azolium azolates from reactions of neutral azoles with 1,3-dimethyl-imidazolium-2-carboxylate, 1,2,3-trimethyl-imidazolium hydrogen carbonate, and N,N-dimethyl-pyrrolidinium hydrogen carbonate

Utilizing previously reported synthetic protocols for the halide- and metal-free synthesis of organic salts, we have prepared a new group of imidazolium and pyrrolidinium azolate anion-based salts demonstrating the general applicability of the methodology and expanding our investigation into non ion exchange routes to potentially energetic ionic liquids. Eighteen salts, out of which six exhibit melting points below 100 °C, were prepared by a simple decarboxylation reaction, which resulted in clean formation of the new compounds without the need for extensive purification. The low stability of the H2CO3 by-product, and its decomposition to CO2 and H2O in aqueous media, allows for purification of the salts by evaporation only.

Hypergolic ionic liquids to mill, suspend, and ignite boron nanoparticles

Boron nanoparticles prepared by milling in the presence of a hypergolic energetic ionic liquid (EIL) are suspendable in the EIL and the EIL retains hypergolicity leading to the ignition of the boron. This approach allows for incorporation of a variety of nanoscale additives to improve EIL properties, such as energetic density and heat of combustion, while providing stability and safe handling of the nanomaterials.

Synthesis, limitations, and thermal properties of energetically-substituted, protonated imidazolium picrate and nitrate salts and further comparison with their methylated analogs

The possibility of forming simple energetic ionic liquids via the straightforward protonation of heterocyclic amines with nitric or picric acid was explored with 1-alkylimidazoles, 1-alkyl-2-methylimidazoles, and nitro, dinitro, and dicyano-substituted derivatives. The melting points of most of the prepared salts were lower than expected and of the 30 compounds prepared, more than half were found to melt below 100 °C. Limitations in the approach were found as a result of the use of energetic electron withdrawing substituents, such as nitro or cyano, which results in a reduction in nucleophilicity of the heterocycle and an inability to form salts with the acids studied. Interesting thermal behavior was observed with several of the new salts including supercooling and crystallization on heating. Comparison of the simple protonated imidazolium nitrate and picrate salts with their methylated analogs indicated that the protonated ionic liquids do not differ substantially in their melting points from the methylated analogs. However, the thermal stabilities of protonated imidazolium salts are much lower than their alkylated derivatives. Nitrate salts with alkylated cations tend to be more thermally stable than the corresponding picrate salts, but with protonated cations, the picrate salts tend to be approximately 70–80 °C more stable than the nitrate salts. Moreover, accelerating rate calorimetry (ARC) revealed that alkylated salts decompose much less exothermically (in some cases endothermically) than the protonated analogs, and that among all the analyzed salts, the most energetic materials found were protonated 1-methylimidazolium nitrate and 1,2-dimethylimidazolium picrate.

Structure and Dynamics of the 1-Hydroxyethyl-4-amino-1,2,4-triazolium Nitrate High-Energy Ionic Liquid System

An investigation of the structure and dynamics of the high-energy ionic liquid, 1-hydroxyethyl-4-amino-1,2,4-triazolium nitrate (HEATN), was undertaken. Both experimental and computational methods were employed to understand the fundamental properties, characteristics, and behavior of HEATN. The charge separation, according to the electrostatic potential derived charges, was assessed. The MP2 (second-order perturbation theory) geometry optimizations find six dimer and five tetramer structures and allow one to see the significant highly hydrogen bonded network predicted within the HEATN system. Due to the prohibitive scaling of ab initio methods, the fragment molecular orbital (FMO) method was employed and assessed for feasibility with highly energetic ionic liquids using HEATN as a model system. The FMO method was found to adequately treat the HEATN ionic liquid system as evidenced by the small relative error obtained. The experimental studies involved the investigation of the solvation dynamics of the HEATN system via the coumarin 153 (C153) probe at five different temperatures. The rotational dynamics through the HEATN liquid were also measured using C153. Comparisons with previously studied imidazolium and phosphonium ionic liquids show surprising similarity. To the authors' knowledge, this is the first experimental study of solvation dynamics in a triazolium-based ionic liquid.

Peculiar Behavior of Azolium Azolate Energetic Ionic Liquids

We present studies of molecular dynamics and interactions in azolium azolate energetic ionic liquids (ILs) by utilizing a variety of physical methods. We observe peculiar rheological behavior for t...

Computational study of proton and methyl cation affinities of imidazole-based highly energetic ionic liquids

The present study deals with the evaluation of gas phase proton and methyl cation affinities for alkyl- and nitrosubstituted imidazoles using DFT (B3LYP)/6-31 + G(d) and MP2 methods in the Gaussian 03 software package. The extent of charge delocalization of these cations is correlated with proton affinity. The study reveals that weakly electron-donating alkyl groups at position 1 of the imidazole enhance its proton affinity, which also increases with increasing alkyl chain length. This is expected to result in an increased tendency to form salts. In contrast, the presence of strongly electron-withdrawing nitro groups lowers proton affinity, which decreases as the number of nitro groups on the ring increases. The same trend is observed for the methyl cation affinity, but to a lower degree. These trends in the proton and methyl cation affinities were analyzed to study the effects of these substituents on the basicity of the energetic imidazole moieties and their tendency to form salts. This, in turn, should aid searches for better highly energetic ionic liquids. In addition, calculations performed on different isomers of mono and dinitroimidazoles show that 5-nitro-1H-imidazole and 2,4-dinitro-1H-imidazole are more stable than the other isomers. Amongst the many nitro derivatives of imidazoles considered in the present study, cations resulting from these two would be the best choice for creating highly energetic ionic liquids when coupled with appropriate energetic anions.

Kinetics of Decomposition of Energetic Ionic Liquids

AbstractThe Arrhenius‐type reaction rate parameters for the initiation reactions governing the thermal decomposition of several energetic ionic liquids (EILs) were determined by numerical techniques. The compounds chosen for this purpose were the energetic 4‐amino‐1,2,4‐triazolium nitrate (4ATN) and 1‐hydroxyethyl‐hydrazinium nitrate (HEHN). The supplementary compounds studied for comparison were 4‐amino‐1,2,4‐triazolium chloride (4ATCl) and ammonium nitrate (AN). The reaction rate parameters were obtained by an evolutionary genetic algorithm (GA) that compared the difference between the experimental and simulated species evolution profiles from the decomposition process. The experimental data were generated by confined rapid thermolysis (CRT). The decomposition process was simulated by applying conservation equations to the condensed and gas phases individually. The optimization module recovered the experimental species profiles with reasonable accuracy for all the compounds studied. The processes governing the decomposition of these energetic compounds were found to be autocatalytic in nature, and the autocatalytic agents were the strong acids generated by the initial decomposition step. The activation energy and pre‐exponential factor for the unimolecular decomposition step for 4ATN, HEHN, and 4ATCl were 167–188 kJ mol−1 and 1016 s−1, respectively, similar to previously determined values for AN.

Confined rapid thermolysis/FTIR/ToF studies of methyl-amino-triazolium-based energetic ionic liquids

Thermal decomposition of the energetic ionic liquids 1-methyl-4-amino-1,2,4-triazolium iodide (Me4ATI), 1-methyl-4-amino-1,2,4-triazolium nitrate (Me4ATN), 1-amino-3-methyl-1,2,3-triazolium iodide (Me1ATI), and 1-amino-3-methyl-1,2,3-triazolium nitrate (Me1ATN) was studied by confined rapid thermolysis. Sub-milligram quantities of the compounds were subjected to decomposition under isothermal conditions achieved by initially heating the sample at rates of approximately 2000 K/s. The products formed by decomposition under the afore-mentioned conditions were sampled by rapid scan FTIR spectroscopy and time-of-flight mass spectrometry. Decomposition studies involving the iodide salts were carried out around 270–290 °C, whereas the nitrate salts were subjected to 320–340 °C. The amino group was found to be involved in the initiation reaction, forming copious quantities of ammonia from the iodide compounds and, N 2O and H 2O from the nitrate compounds. The extent of decomposition of the triazole ring was minimal at the considered temperatures.

Inorganic or Organic Azide-Containing Hypergolic Ionic Liquids⊥⊥ As poster published in 1st Korean International Symposium on High Energy Materials, Incheon, Korea, October 6−9, 2009.

Recently extensive research has focused on replacing toxic hydrazine, monomethylhydrazine, and unsymmetrical dimethylhydrazine as liquid propellant fuels. 2-Azido-N,N-dimethylethylamine (1) is a good candidate to replace hydrazine derivatives in certain hypergolic fuel applications. Energetic ionic liquids that contain the 2-azido-N,N,N-trimethylethylammonium cation with nitrocyanamide, dicyanamide, dinitramide, or azide anion have been successfully synthesized in good yields by metathesis reactions. Ionic liquids have received considerable attention as energetic materials. The replacement of hydrazine with tertiary ammonium salts is especially attractive since many ionic liquids are models for green chemistry. In this work, new azide-functionalized ionic liquids are demonstrated to exhibit hypergolic activity with such oxidizers as 100% nitric acid or nitrogen tetraoxide (NTO).

Ionic Liquids Based on Azolate Anions

Compartmentalized molecular level design of new energetic materials based on energetic azolate anions allows for the examination of the effects of both cation and anion on the physiochemical properties of ionic liquids. Thirty one novel salts were synthesized by pairing diverse cations (tetraphenylphosphonium, ethyltriphenylphosphonium, N-phenyl pyridinium, 1-butyl-3-methylimidazolium, tetramethyl-, tetraethyl-, and tetrabutylammonium) with azolate anions (5-nitrobenzimidazolate, 5-nitrobenzotriazolate, 3,5-dinitro-1,2,4-triazolate, 2,4-dinitroimidazolate, 4-nitro-1,2,3-triazolate, 4,5-dinitroimidazolate, 4,5-dicyanoimidazolate, 4-nitroimidazolate, and tetrazolate). These salts have been characterized by DSC, TGA, and single crystal X-ray crystallography. The azolates in general are surprisingly stable in the systems explored. Ionic liquids were obtained with all combinations of the 1-butyl-3-methylimidazolium cation and the heterocyclic azolate anions studied, and with several combinations of tetraethyl- or tetrabutylammonium cations and the azolate anions. Favorable structure-property relationships were most often achieved when changing from 4- and 4,5-disubstituted anions to 3,5- and 2,4-disubstituted anions. The most promising anion for use in energetic ionic liquids of those studied here, was 3,5-dinitro-1,2,4-triazolate, based on its contributions to the entire set of target properties.

Confined rapid thermolysis/FTIR/ToF studies of tetrazolium-based energetic ionic liquids

The initiation of decomposition of several energetic ionic liquids (EILs) was studied by confined rapid thermolysis. Rapidscan FTIR spectroscopy and time-of-flight mass spectrometry were utilized to identify the products evolved from sub-milligram quantities subjected to heating rates of about 2000 K/s. The compounds studied were 2-amino-4,5-dimethyl-tetrazolium iodide (2AdMTZI), 2-amino-4,5-dimethyl-tetrazolium nitrate (2AdMTZN), 1-amino-4,5-dimethyl-tetrazolium iodide (1AdMTZI), and 1-amino-4,5-dimethyl-tetrazolium nitrate (1AdMTZN). Decomposition studies involving the 2AdMTZ salts were carried out around 300 °C. The major decomposition pathway involves a nucleophilic transfer to the anion leading to the formation of methyl iodide and methyl nitrate, from 2AdMTZI and 2AdMTZN, respectively. Methyl iodide ( m/ z = 142) was detected both in the ToFMS and FTIR spectra. Methyl nitrate ( m/ z = 77) was visible in the FTIR spectra. The resultant nitrogen-rich amino-methyl-tetrazole ( m/ z = 99) was found to decompose to form primarily molecular nitrogen and methyl isocyanide. Unlike the 2AdMTZ salts, the 1AdMTZ salts were found to initiate decomposition at temperatures lower by at least 50 °C. Decomposition was found to proceed through three major pathways—formation of the corresponding methylated anion and 1-amino-5-methyl-tetrazole, formation of ammonia by the amino group, and expulsion of nitrogen from the tetrazole cation itself. 1-Amino-5-methyl tetrazole was found to rapidly decompose to form mainly ammonia and nitrogen. The ammonia formed in the condensed phase during the decomposition of 1AdMTZN was reduced by methyl nitrate, to form smaller molecular weight species, such as N 2O, H 2O, NO 2, NO, CO 2, and others.

Direct, Atom Efficient, and Halide‐Free Syntheses of Azolium Azolate Energetic Ionic Liquids and Their Eutectic Mixtures, and Method for Determining Eutectic Composition

Three in a row: We report i) the successful halide-free, efficient syntheses of azolium azolates by reaction of 1,3-dimethylimidazolium-2-carboxylate with neutral azoles (by a one-pot synthesis with an easy to remove byproduct (CO2 gas, see scheme), ii) the development of a facile, low sample demand method for ready determination of the eutectic point compositions of mixtures of these salts, and iii) the application of the new synthetic techniques for the direct preparation of the eutectic mixtures.

Energetic Ionic Liquids based on Lanthanide Nitrate Complex Anions

Energetic ionic liquids based on anionic lanthanide nitrate complexes Cat(+) (3)[Ln(NO(3))(6)](3-), where Cat(+) is guanidinium, 4-aminotriazolium, 4-amino-1-methyltriazolium, 4-amino-1-ethyltriazolium, 4-amino-1-butyltriazolium, 1,5-diaminotetrazolium, and 1,5-diamino-4-methyltetrazolium, were prepared. The hexanitratolanthanate (-cerate) salts with the last two cations, which are the first CO-balanced energetic ionic liquids that are stable to hydrolysis and air, have impact sensitivities of about 27 J. These ionic liquids were obtained by an environmentally friendly, simple method using nitrate-containing precursors. All salts were fully characterized by IR and NMR spectroscopy, elemental analysis, and determination of thermal stability, phase behavior, density, and water content. According to theoretical calculations, these new compounds have potential as propellants.

Energetic Ionic Liquids Based on Anionic Rare Earth Nitrate Complexes

not Available.