Highly dense nitrogen-rich ionic compounds are potential high-performance energetic materials for use in military and industrial venues. Guanazinium salts with promising energetic anions and a family of energetic salts based on nitrogen-rich cations and the 6-nitroamino-2,4-diazido[1,3,5]triazine anion (NADAT) were prepared and fully characterized by elemental analysis, IR spectroscopy, 1H NMR and 13C NMR spectroscopy, and differential scanning calorimetry (DSC). The crystal structures of neutral NADAT (2) and its biguanidinium salt 5 were determined by single-crystal X-ray diffraction (2: orthorhombic, Pnma; 5: monoclinic, P21). Additionally, the isomerization behavior of 2 in solution was investigated by proton-decoupled 13C and 15N NMR spectroscopy. All the new salts exhibit desirable physical properties, such as relatively high densities (1.63–1.78 g cm−3) and moderate thermal stabilities (Td = 130–196 °C for 3–10 and 209–257 °C for 11–15). Theoretical performance calculations (Gaussian 03 and Cheetah 5.0) gave detonation pressures and velocities for the ionic compounds 3–15 in the range of 21.0–30.3  GPa and 7675–9048 m s−1, respectively, which makes them competitive energetic materials.

Nitrogen-rich salts based on energetic nitroaminodiazido[1,3,5]triazine and guanazine.

1-Nitroamino-1,2,3-triazole (5) was synthesized and its zwitterionic structure was established using single-crystal X-ray diffraction. The calculated detonation properties for 4-nitroamino-1,2,4-triazole (2) (P = 33.4 GPa, vD = 8793 m/s) and 1-nitroamino-1,2,3-triazole (5) (P = 33.0 GPa, vD = 8743 m/s) are comparable with RDX. A new family of energetic salts 7–21 based on either the 1-nitroamino-1,2,3-triazolate or the 4-nitroamino-1,2,4-triazolate anion were prepared and characterized by vibrational spectroscopy (IR), multinuclear NMR spectra, elemental analyses, density, TGA and DSC. The heats of formation (ΔfH°298) and detonation properties for these stable salts were calculated using Gaussian 03 and Cheetah 4.0, respectively. Comparison of the properties of the 1,2,3- and 1,2,4-triazolate salts indicates that while the 1,2,4-derivatives are more stable thermally, the 1,2,3-analogs invariably have higher heats of formation. In contrast to its salts, 1-nitroamino-1,2,3-triazole (5) is extremely shock-sensitive with an impact sensitivty of <1 J. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Nitroamino Triazoles: Nitrogen‐Rich Precursors of Stable Energetic Salts

The most comprehensive approach to analyze and characterize energetic materials is suggested and applied to enable rational, rigorous design of novel materials and targeted improvements of existing materials to achieve desired properties. We report synthesis, characterization of the structure and sensitivity, and modeling of thermal and electronic stability of the energetic, heterocyclic compound, 3,4-bis(4-nitro-1,2,5-oxadiazol-3-yl)-1,2,5-oxadiazole-2-oxide (BNFF). The proposed novel, relatively simple synthesis of BNFF in excellent yields allows for an efficient scale up. Performing careful characterization indicates that these materials offer an unusual combination of properties and exhibit a relatively high energy density, high and controllable stability against decomposition, low melting temperature, and low sensitivity to initiation of detonation. First-principles calculations of activation barriers and reaction rate constants reveal the decomposition scenarios that govern the thermal stability and...

Searching for Low-Sensitivity Cast-Melt High-Energy-Density Materials: Synthesis, Characterization, and Decomposition Kinetics of 3,4-Bis(4-nitro-1,2,5-oxadiazol-3-yl)-1,2,5-oxadiazole-2-oxide

First principles total energy calculations were combined with variational transition state theory to reveal a surface-induced effect on the decomposition of a molecular material. Explored decomposition reactions were illustrated with energetic molecular solid β-cyclotetramethylene-tetranitramine. Simulated N–NO2 homolysis reactions demonstrated that initiation of molecular material’s degradation is characterized by a reduced activation barrier and significantly accelerated reaction rates for molecules that are placed on a free surface, an internal void, or a vacancy as compared to the perfect bulk crystal.

Surface-Enhanced Decomposition Kinetics of Molecular Materials Illustrated with Cyclotetramethylene-tetranitramine

The pathways corresponding to the most energetically favorable decomposition reactions that can be envisaged for o-nitrotoluene (and 20 of its derivatives) have been studied, using density functional theory, in order to evaluate the influence of substituents’ nature (nitro, methyl, amino, carboxylic acid, and hydroxyl) and position. The first mechanism consists of the direct dissociation (homolysis) of the carbon nitrogen bond (CH3C6H4NO2 = CH3C6H4 + NO2) whereas the second one is a more complex process initiated by C−H alpha attack and leading to the formation of anthranil and water (C6H4C(H)ON + H2O). For each compound, the initial step of this last channel is the rate limiting one, the Gibbs activation energy of all systems being very close, that is all in the 40−44 kcal/mol range. More important variations have been observed for the C−NO2 homolysis Gibbs activation energies (46−60 kcal/mol). These variations have been related to electron donor−acceptor properties of substituents by considering signifi...

A theoretical study of the decomposition mechanisms in substituted o-nitrotoluenes.

Possible decomposition mechanisms of C-nitro-and N-nitro-1,2,4-triazoles were simulated. We showed that in addition to the experimentally detected thermolysis products including N2, N2O, NO, CO2, HCN, HNCO, 1,2,4-triazole, 3(5)-nitroso-1,2,4-triazole, and 1,2,4-triazolone, some other decompositon products (H2O, CO, NO2, cyanamide, cyanuric acid, and melamine) can be formed. Using the density functional approach (B3LYP/6-31G* approximation), we assessed the most favorable thermal decomposition pathways of nitrotriazoles and studied the relationships between the thermolysis pathways of these substances and their molecular and electronic structures. We found a correlation between the energy gap width (energy difference between the frontier molecular orbitals) and the stabilities of the C-nitro-1,2,4-triazole tautomers to thermal decomposition.

Thermal decomposition mechanisms of nitro -1,2,4 -triazoles : a theoretical study

Data on the experimental and theoretical studies of thermal decomposition of C- and N-nitro compounds of aliphatic, alicyclic, aromatic and heteroaromatic compounds, which formed the grounds for the develpment of ab initio appoach to the prediction of the mechanisms of thermolysis of energetic compounds, are described systematically. The relationships between the structures and thermolysis mechanisms of compounds based on differentiation of the structural fragments depending on the functional surrounding of nitro groups are identified. Using the RRN (Recombination Reaction Network) strategy and original CASB (Computer Assisted Structure Building) softwere, full reaction mechanisms for the thermal destruction of nitro compounds at different thermal decomposition levels (including extensive ones) are simulated. The full set of possible mechanisms of thermal decomposition of 38 chemically different nitro compounds is presented

Differentiation of the molecular structure of nitro compounds as the basis for simulation of their thermal destruction processes

Modeling of the probable mechanisms of the thermolysis of C-and N-nitramino-1,2,4-triazoles has been carried out by methods of mathematical chemistry. It was established that the formation is possible of a more diverse spectrum of products in their destruction than was previously recorded by different experimental methods. Subsequent assessment of the thermochemical preference for pathways of decomposition of the compounds was carried out by the density functional method in the B3LYP/6-31G* approach. It was determined that the thermal destruction of C-and N-nitramino-substituted polynitrogen heterocycles, capable of tautomeric conversion, was most probably through the thermochemically least stable nitramine form. Thermal decomposition of the considered tautomers is preferred at the NNO2 fragment and not at the triazole ring. The direction of the structural stabilization of the investigated compounds has been clarified by comparison of the geometric, electronic, and thermochemical characteristics of C-NNO2-and N-NNO2-substituted 1,2,4-triazoles.

Molecular modeling of the mechanisms of thermolysis of nitramino-1,2,4-triazoles

We have used MNDO and PM3 approximations and the density functional method (6–31G*) for a quantum chemical study of the structure and some physicochemical properties of N-nitro and N-nitroso derivatives of piperazine, furazano[3,4-b]piperazine, and bisfurazano[3,4-b;3′,4′-e]piperazine. We have analyzed the structural, electronic, and thermochemical characteristics and the enthalpies of formation for the compounds in the gas phase and in the solid phase. We have found a correlation between the strength of the N-N bond and the N-N bond length, the pyramidality of the nitrogen atom of the piperazine ring, and the size of the energy gap between the frontier orbitals. Based on calculations by the density functional method, we have carried out a comparative analysis of the thermochemical stability of the compounds in homolytic reactions.

T. V. Petukhova

Papers

Thermal decomposition mechanisms of nitro -1,2,4 -triazoles : a theoretical study

Differentiation of the molecular structure of nitro compounds as the basis for simulation of their thermal destruction processes

Molecular modeling of the mechanisms of thermolysis of nitramino-1,2,4-triazoles

Quantum-chemical study of the structure and thermochemical properties of nitropiperazines and nitrosopiperazines

Differentiation of the Molecular Structures of Nitro Compounds as the Basis for Simulation of Their Thermal Destruction Processes