Triazolium-Based Energetic Ionic Liquids

Replacement of Toxic Hydrazines in Satellite Propulsion with Greener Dinitramide-Based Energetic Ionic Liquid Candidates

Satellite propulsion uses liquid mono or bi-propellants composed of a hydrazine in combination with a strong oxidant. However, hydrazines are highly toxic. As a result, many research efforts for more environmentally compatible propellants have been made over the past decade. In this study we evidence green formulations that retain high propulsive performances. They are based on the dinitramide anion. From an initial library of 37 ammonium dinitramides 3 best candidates were selected after evaluation of their potential syntheses, calculated theoretical performances, experimental synthesis optimizations and decomposition temperatures. These three salts were then formulated to obtain acceptable sensitivities and melting points, which eventually led to only one formulation being retained: a 40 : 60 mixture of dimethylammonium dinitramide and ammonium dinitramide phlegmatized by 10 % of glycerol.

Gel Polymer Electrolytes with Mixture of Triazolium Ionic Liquids and Propylene Carbonate

This study is focused on the structural influence of 1,2,4-triazolium ionic liquid (IL), that is, the effect of the length of the substituent and the type of substitution (1-methyl-4-alkyl or 1-alkyl-4-methyl) used in the mixture with propylene carbonate (PC) on the properties of thiol–ene polymer ionogels and on the preparation of an ionogel with satisfactory mechanical and conductive properties. PC allows for higher conductivity but also causes electrolyte leakage from the gel. When using triazolium IL (instead of the imidazolium one), because of the stronger interactions between components of the system, the ionogels do not leak. In this study, 1,4-dialkyl-1,2,4-triazolium ILs were successfully synthesized by the alkylation of 1,2,4-triazole. Subsequently, gel polymer electrolytes were obtained by one-pot thiol–ene photopolymerization reactions of tetrafunctional thiols with different chemical structures: pentaerythritol tetra(3-mercaptopropionate) (PETMP) or pentaerythritol tetra(3-mercaptobutyrate) (PETMB) and trifunctional ene (TATT) in the presence of a mixture of 1,4-dialkyl-1,2,4-triazolium IL with PC. Measurements made by electrochemical impedance spectroscopy showed that all ionogels with TATT+PETMB as a polymer matrix presented smaller relative ionic conductivity compared to ionogels containing TATT+PETMP. The puncture resistance and elongation at puncture, measured by the puncture resistance method, were higher for ionogels with poly(TATT+PETMB) than for those with poly(TATT+PETMP). Moreover, ILs containing a methyl group in position N1 of the 1,2,4-triazole ring presented lower puncture resistance than ionogels with ILs containing a methyl group in position N4, especially for shorter alkyl chains. Additionally, the photo-differential scanning calorimetry method was employed to characterize the course of photopolymerization. The compositions and their constituents were characterized by UV and IR spectroscopy.

Mechanistic Insights into the Formation of 1-Alkylidene/Arylidene-1,2,4-triazolinium Salts: A Combined NMR/Density Functional Theory Approach

In a recent report on the synthetic approach to the novel substance class of 1-alkylidene/arylidene-1,2,4-triazolinium salts, a reaction mechanism suggesting a regioselective outcome was proposed. This hypothesis was tested via a combined NMR and density functional theory (DFT) approach. To this end, three experiments with 13C-labeled carbonyl reactants were monitored in situ by solution-state NMR. In one experiment, an intermediate as described in the former mechanistic proposal was observed. However, incorporation of 13C isotope labels into multiple sites of the heterocycle could not be reconciled with the "regioselective mechanism". It was found that an unproductive reaction pathway can lead to 13C scrambling, along with metathetical carbonyl exchange. According to DFT calculations, the concurring reaction pathways are connected via a thermodynamically controlled cyclic 1,3-oxazetidine intermediate. The obtained insights were applied in a synthetic study including aliphatic ketones and para-substituted benzaldehydes. The mechanistic peculiarities set the potential synthetic scope of the novel reaction type.

Design and exploration of 5-nitro-3-trinitromethyl-1H-1,2,4-triazole and its derivatives as energetic materials

According to the fact that 5-nitro-3-trinitromethyl-1H-1,2,4 triazole (NTNMT) is a successful, good explosive, energetic groups such as -CH3, -NH2, -NHNO2, -NO2, -ONO2, -NF2, -CN, -NC, -N3 groups were introduced into NTNMT and their oxygen balance was at about zero. The energetic properties, detonation performance, and sensitivity were studied at the B3LYP/6-31G** level of density functional theory to seek for possible high energy density compounds. The effects of substituent groups on heat of formation (HOF), density ρ, detonation velocity D, detonation pressure P, detonation energy Q, and sensitivity (evaluated using oxygen balance OB, the nitro group charges -QNO2, and bond dissociation energies BDE were studied and discussed. The order of contribution of the substituent groups to ρ, D, and P was -NF2 > -ONO2 > -NO2 > -NHNO2 > -N3 > -NH2 > -NC > -CN > -CH3; while to HOF is -N3 > -NC > -CN > -NO2 > -NF2 > -ONO2 > -NH2 > -NHNO2 > -CH3. The trigger bonds in the pyrolysis process for NTNMT derivatives may be N-NO2, N-NH2, N-NHNO2, C-NO2, or O-NO2 varying with the attachment of different substituents. Results show that NTNMT-NHNO2, -NH2, -CN, and -NC derivatives have high detonation performance and good stability. In a word, the oxygen balance at about zero strategy in this work offers new routes for the improvement in properties and stabilities of energetic materials. In the present paper, several 5-nitro-3-trinitromethyl-1H-1,2,4 triazole (NTNMT) derivatives were designed. Their energetic properties, detonation performance, and sensitivity were studied at the B3LYP/6-31G** level of density functional theory (DFT) to seek for possible high energy density compounds (HEDCs). The different substituents have some changes in the influence on heat of formation (HOF), density ρ, detonation velocity D, detonation pressure P, detonation energy Q, and sensitivity. In a word, the oxygen balance at about zero strategy in this work offers new routes for the improvement in properties and stabilities of energetic materials.

Amino-tetrazole functionalized fused triazolo-triazine and tetrazolo-triazine energetic materials

In this study, two insensitive energetic compounds using fused triazolo-triazine and tetrazolo-triazine as the framework, one amino and one tetrazole as functional groups, were prepared through a two-step reaction.

Theoretical design of novel energetic salts derived from bicyclo-HMX

We designed three novel cage energetic anions by introducing ionic bridges containing NΘ, N(OΘ) and N(NΘNO₂) into cis-2,4,6,8-tetranitro-1H,5H-2,4,6,8- tetraazabicyclo[3.3.0] octane (bicyclo-HMX or BCMHX). The properties of 21 energetic salts, based on cage anions and ammonium-based cations, were studied by density functional theory (DFT) and volume-based thermodynamics (VBT) calculations. Compared to the parent nonionic BCHMX, most title salts have lower predicted impact sensitivities, higher predicted densities, larger predicted heats of formation (HOFs) and better predicted detonation properties. In particular, 11 energetic salts not only exhibit excellent predicted energetic properties, superior to 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20), but also have lower predicted sensitivity than CL-20. The best salt had a predicted detonation velocity of 10.06 km s^-1, a predicted detonation pressure of 48.54 GPa and a predicted sensitivity (h₅₀) of 23.99 cm. By introducing ionic bridges into highly nitrated rings, or modifying the original bridge with ionic bridges, some highly nitrated cage compounds with both excellent performance and low sensitivity can be developed strategically. Graphical abstract Heats of detonation, detonation velocities, and detonation pressures of salts derived from bicyclo-HMX.

Density functional study of guanidine-azole salts as energetic materials

A series of guanidine cations and azole anions were designed for use as energetic salts. Their geometrical structures were optimized by the density functional theory (DFT) method. The counter ions were matched by the similar magnitude of the electron affinity (EA) of the cation and the ionization potential (IP) of the anion. The densities, heats of formation, detonation parameters, and impact sensitivity were predicted. The incorporation of guanidine cations and diazole anions are favorable to form thermal stable salts except cation A1. The diaminoguanidine cation has greater impact on the density and detonation properties of the salts than the triaminoguanidine cation. 2-Amino-3-nitroamino-4,5-nitro-dinitropyrazole is the best anion for advancing the detonation performance among all the anions. Incorporating the C=O bond into the guanidine cations enhances the density and detonation performance of the guanidine-azole salts. The salts containing III1–III4 anion have better detonation properties than HMX, indicating that these salts are potential energetic compounds. Compared with RDX or HMX, some salts with diaminoguanidine cation display lower impact sensitivity.

Proton Transfer in 1,2,4-Triazolium Dinitramide: Effect of Aqueous Microsolvation

The gas phase proton transfer process in 1,2,4-triazolium dinitramide (TD) was studied using second-order perturbation theory to determine how the presence of one and two water molecules modifies the potential energy surface that connects the ion pair to the neutral pair. The presence of one water molecule can introduce small proton transfer energy barriers that separate the ion pair from the lower-energy neutral pair. These energy barriers are easily surmounted. Reaction paths were determined for single proton transfers and double proton transfers via one water molecule. In the presence of two water molecules, the global minimum is an ion pair, as are most of the lower-energy local minima. Energy barriers for single, double, and triple proton transfers were also found for TD in the presence of two water molecules. One TD ion pair structure with two water molecules has no corresponding neutral pair energy minimum. A quasi-atomic orbital analysis is used to understand the nature of the bonding in the various species studied in this work.

Effect of Boron Clusters on the Ignition Reaction of HNO3 and Dicynanamide-Based Ionic Liquids

Many ionic liquids containing the dicynamide anion (DCA^-, formula N(CN)₂^-) exhibit hypergolic ignition when exposed to the common oxidizer nitric acid. However, the ignition delay is often about 10 times longer than the desired 5 ms for rocket applications, so that improvements are desired. Experiments in the past decade have suggested both a mechanism for the early reaction steps and also that additives such as decaborane can reduce the ignition delay. The mechanisms for reactions of nitric acid with both DCA^- and protonated DCAH are considered here, using accurate wave function methods. Complexation of DCA^- or DCAH with borane clusters B₁₀H₁₄ or B₉H₁₄^- is found to modify these mechanisms slightly by changing the nature of some of the intermediate saddle points and by small reductions in the reaction barriers.

Insensitive ionic bio-energetic materials derived from amino acids

Energetic salts/ionic liquids have received increasing attention as fascinating energetic materials, and the use of renewable compounds is a promising approach to developing energetic materials. Until recently, biomolecules have been used as raw materials to develop neutral energetic compounds, whereas research focused on ionic energetic materials obtained from natural bio-renewable frameworks is scarce. This work systematically investigates ionic bio-energetic materials (IBEMs) derived from sustainable natural amino acids. In addition to combustibility, high density, good thermal stability, and one-step preparation, these IBEMs demonstrated apparent hypotoxicity and insensitivity. Moreover, a theoretical examination was performed to explore their appropriate properties. The intriguing results of this study indicates that IBEMs are potential bio-based energetic materials.

Energetic compounds featuring bi(1,3,4-oxadiazole): a new family of insensitive energetic materials

Energetic compounds featuring bi(1,3,4-oxadiazole) with good detonation performances and acceptable sensitivities were synthesized.

Replacement of 2,4,6-trinitrotoluene by two eutectics formed between 4-amino-1,2,4-triazolium nitrate and 4-amino-1,2,4-triazolium perchlorate

Mixtures of 4-ATN and 4-ATP were submitted to DSC and a binary phase diagram was constructed by using DSC data.

Insensitive energetic 5-nitroaminotetrazolate ionic liquids

Combustible 5-nitroaminotetrazolate-based energetic ionic liquids with high stability as well as environmentally friendly decomposition gases were prepared and fully characterized.

A DFT-D study on the stability and intramolecular interactions of the salts of 1,2,3- and 1,2,4-triazoles

Nitrogen-rich 1,2,4-triazole (1) and 1,2,3-triazole (2) react as bases with the oxygen-rich acids HNO3 (a), HN(NO2)2 (b), and HClO4 (c) to produce energetic salts (1a, 1b, and 1c and 2a, 2b, and 2c, respectively) potentially applicable to composite explosives and propellants. In this study, these salts were studied with the dispersion-corrected density functional theory. For the isomers such as 1a and 2a, the more negative ΔrGm of the formation reaction leads to a higher thermally stable salt. The ability to form intramolecular hydrogen bonds predicted with the quantum theory of atoms in molecules has the order of 2 > 1. Different hydrogen bonds result in different second-order perturbation energies, redshifts in IR, and electron density differences. The charge transfer, binding energy, dispersion energy, lattice energy, and energy gap between frontier orbits in the salts of 1 are larger than those of 2, which is helpful for stabilizing the former, and 1 is more obviously stabilized than 2 by formation of salts. Different conformations of 1 and 2 hardly affect the frontier orbital distributions. Base 1 is a more preferred base than 2 to form salts.

A comprehensive analysis of molecule-intrinsic quasi-atomic, bonding, and correlating orbitals. I. Hartree-Fock wave functions

Through a basis-set-independent web of localizing orbital-transformations, the electronic wave function of a molecule is expressed in terms of a set of orbitals that reveal the atomic structure and the bonding pattern of a molecule. The analysis is based on resolving the valence orbital space in terms of an internal space, which has minimal basis set dimensions, and an external space. In the internal space, oriented quasi-atomic orbitals and split-localized molecular orbitals are determined by new, fast localization methods. The density matrix between the oriented quasi-atomic orbitals as well as the locations of the split-localized orbitals exhibit atomic populations and inter-atomic bonding patterns. A correlation-adapted quasi-atomic basis is determined in the external orbital space. The general formulations are specified in detail for Hartree-Fock wave functions. Applications to specific molecules exemplify the general scheme.

Structure, Thermal Behaviour, and Energetic Properties of 4-Amino-1,2,4-triazole Dinitroguanidine Salt

A novel nitrogen-rich energetic compound 4-amino-1,2,4-triazole dinitroguanidine salt (4-ATDNG) was synthesized and fully characterized. Its crystal, thermal behaviour, and detonation properties were investigated by X-ray diffraction, thermogravimetry-derivative thermogravimetry-differential scanning calorimetry (TG-DTG-DSC) coupling system, and the Kamlet–Jacobs equation. In view of the obtained values such as the critical temperature of thermal explosion (Tb, 186.36°C), entropy of activation (ΔS≠, 60.22 J mol–1 k–1), enthalpy of activation (ΔH≠, 143.24 kJ mol–1), free energy of activation (ΔG≠, 116.34 kJ mol–1), detonation pressure (P, 29.78 GPa), detonation velocity (V, 8.28 km s–1), and impact sensitivity (h50 = 135 cm), it is proposed that 4-ATDNG possesses excellent thermal stability and has the potential to be a useful energetic material in the future.

Bis(1,5-diamino-4-methyl-tetrazolium)hydrazinetetrazolate: synthesis, structure and energetic properties

Bis(1,5-diamino-4-methyl-tetrazolium)hydrazinetetrazolate (BMDATHBT) was synthesized for the first time from 1,5-diamino-4-methyl-tetrazolium sulfate (MDATS) and hydrazino bitetrazole barium (HBTBa·5H₂O) as raw materials.

A comparative theoretical study of heterocycle-functionalized tetrazolate- and tetrazolate-1-oxide-based dianionic salts

Density functional theory and volume-based thermodynamics calculations have been performed to study the crystal densities, heats of formation, energetic properties, thermodynamics of formation, and impact sensitivity for a series of heterocycle-functionalized tetrazolate- and tetrazolate1-oxide-based dianionic salts. The results show that the hydroxylammonium cation is better than the tetrazolium cation for increasing the densities and detonation performance of the tetrazolate dianionic salts. The salts containing series B (tetrazolate-1-oxide) have larger densities and detonation performance than corresponding ones containing series A (tetrazolate) with the same cation. Incorporating a zwitterionic N-oxide into the nitrogen system is helpful for increasing its density and detonation performance for each salt series, but it is not favorable for improving its heat of formation. The salt including the tetrazine-dioxide conjugated with two tetrazolide exhibits the best energetic performance. The salts containing the tetrazolium cation could be possibly synthesized by the proposed reactions. Some of the salts with the cation hydroxylammonium show lower impact sensitivity than RDX or HMX.

Theoretical studies of energetic nitrogen-rich ionic salts composed of substituted 5-nitroiminotetrazolate anions and various cations

We have performed density functional theory and volume-based thermodynamics calculations to study the effects of different combinations of energetic anions and cations on the crystal densities, heats of formation, energetic properties, and thermodynamics of formation for a series of 5-nitroiminotetrazolate-based ionic salts. The results show that the substitution of the -NO2, -NF2, -N3, or -C(NO2)3 group is helpful for increasing the densities of the salts. Incorporating every substituent (-NH2, -NO2, -NF2, -N3, or -C(NO2)3) into the salt is favorable for improving its HOF and detonation performance. Incorporating the cation B1, B2, B10, or B11 into the salts is helpful for improving its detonation properties. Increasing negative charge for the 5-nitroiminotetrazolate-based salts is unfavorable for enhancing the density and detonation performance, but is helpful for increasing the HOFs. Many salts present comparable detonation performance with commonly used explosives RDX or HMX. Among them, 21 salts have near or better properties than HMX. The thermodynamics of formation of the salts show that the majority of the 5-nitroiminotetrazolate salts with the cation B1, B3, B9, B10, B12 could be synthesized by the proposed reactions.

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.