Thermal Rearrangement of 1,4-Dinitroimidazole to 2,4-Dinitroimidazole: Characterization and Investigation of the Mechanism by Mass Spectrometry and Isotope Labeling

Polynitro-N-aryl-C-nitro-pyrazole/imidazole Derivatives: Thermally Stable-Insensitive Energetic Materials

A wide array of methoxy-substituted-polynitro-aryl-pyrazole/imidazoles with readily oxidizable -NH₂/NO₂/NHNO₂/diazo functional groups is synthesized. Single crystal X-ray diffraction (XRD) analysis confirms the molecular structure of the compounds. Energetic properties of the synthesized compounds are determined by theoretical and experimental studies. Most of the compounds are thermally stable and insensitive to impact and friction. Some of the molecules possess better detonation velocity and detonation pressure over TNT.

Comparative Quantum Chemistry Study on the Unimolecular Decomposition Channels of Pyrazole and Imidazole Energetic Materials

The difference in the initial decomposition step of pyrazoles and imidazoles was explored using the M062X method for optimization and G4-MP2 and approximated CCSD(T) methods for energies. Laplacian bond order analysis was used to study the effect of the nitro group on the bond strength and predict the bond dissociation energy (BDE) of the ring. Thermochemistry results show that the most possible decay channel of 1H-pyrazole and 3-nitropyrazole is the N₂ elimination, while the preferred initial step of 1H-imidazole is the CHN elimination. However, the nitro-nitrite isomerization dominates the decomposition of other nitro derivatives of 1H-pyrazole and 1H-imidazole. As for the formation of HO and HONO, the high energy barrier makes it difficult to take place. Based on the analysis of the lowest energy barrier and the BDE of NO₂ loss, it can be concluded that imidazoles are more stable than pyrazoles. This work contributes to revealing the difference in the initial step of energetic isomers and the understanding of the decomposition mechanism of energetic azoles.

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.

Thermal stability and detonation character of nitro-substituted derivatives of imidazole

A series of nitro-imidazole derivatives were designed by replacing hydrogen atoms on imidazole ring with nitro group one by one. In order to investigate the thermodynamic stability, heat of formation (HOF), and bond dissociation energy (BDE) are calculated at the B3PW91/6-311+G(d,p) level. In order to investigate the impact sensitivity and detonation property, the drop height (H₅₀), free space per molecule in crystal lattice (ΔV), detonation velocity (D), and detonation pressure (P) are calculated by using the empirical Kamlet-Jacobs (K-J) equation. The results show that the thermal stabilities of title molecules are determined by whether nitro group is associated to 1-position or not and accompanied with the steric hindrance between nitro groups and the charge population on the carbon atoms of imidazole ring. The excellent impact sensitivity and detonation performance of title molecules are also evaluated. On the consideration both of stability and detonation characters, 2,4,5-trinitro-1H-imidazole (D = 8.98 km/s, P = 36.70 GPa) is screened out as the potential high-energy-density molecule for further research.

15N labeling and analysis of 13C–15N and 1H–15N couplings in studies of the structures and chemical transformations of nitrogen heterocycles

This review provides a generalization of effective examples of ¹⁵N labeling followed by an analysis of J_CN and J_HN couplings in solution as a tool to study the structural aspects and pathways of chemical transformations in nitrogen heterocycles.

Model free isoconversional procedure for evaluating the effective activation energy values of thermally stimulated processes in dinitroimidazoles

The decomposition kinetics of 1,4-dinitroimidazole, 2,4-dinitroimidazole, and N-methyl-2,4-dinitroimidazole have been investigated using thermogravimetry-differential thermal analysis technique under N2 atmosphere at the flow rate 100 cm(3)/min. The Flynn-Wall-Ozawa method and the Friedman method were used for the estimation of the effective activation energy values. These model free isoconversional kinetic methods showed variation in the calculated values due to the approximation of temperature integral used in the derivations of the kinetic equations. The model compounds were decomposed by multi-step kinetics evident from the nonlinear relationship of the effective activation energy values with the conversion rate. Three different reaction pathways namely NO2 elimination, NO elimination, and HONO elimination are expected to play crucial role in the decomposition of nitroimidazoles. The model dinitroimidazoles represent different decomposition kinetics, and the reaction pathways the NO2 elimination, and NO elimination compete with each other for the decomposition mechanism. The present study is certainly helpful in understanding the decomposition kinetics, and dynamics of substituted nitroimidazoles to be used for fuel, and explosive applications.

Quantum-chemical studies on thermodynamic feasibility of 1-methyl-2,4,5-trinitroimidazole processes

1-Methyl-2,4,5-trinitro imidazole (MTNI) is a well-known melt cast explosive possessing good thermal stability and impact insensitivity. MTNI has been synthesized from multi-step nitration followed by methylation of imidazole exhibiting low yield. It is desirable to screen the process thermodynamically for evaluating feasibility of the process. In the present investigations, B3LYP method in combination with 3-21G** basis set has been chosen to evaluate the enthalpy of formation for reaction species by designing reasonable isodesmic reactions. Thermodynamic feasibility of the processes has been worked out assuming free energies of reactions as derived from standard enthalpy and entropy of the reaction species. All possible synthesis routes for the target molecule, MTNI has been conceptualized from different precursors/intermediates viz. imidazole, 2-nitroimidazole, 4-nitroimidazole, 1-methyl imidazole and 2,4,5-triiodoimidazole. Various nitrating agents have been employed and their effect studied for deciding the feasibility of the reaction. It has been found that reaction entropy and enthalpy are favorable on usage of NO2BF4 as nitrating agent. The charge on nitro group (-QNO2) has been used for better understanding of the reactivity of substrates/intermediates. Overall, the study helped in screening several possible routes for MTNI synthesis and identified the thermodynamically feasible process by using NO2BF4 as nitrating agent.

A comparative study on vibrational, conformational and electronic structure of 1,2-dimethyl-5-nitroimidazole and 2-methyl-5-nitroimidazole

The FTIR and FT-Raman spectra of 1,2-dimethyl-5-nitroimidazole and 2-methyl-5-nitroimidazole have been recorded in the regions 4000-400 and 4000-100 cm(-1), respectively. The conformational analyses were performed and the energies of the different possible conformers were determined. The geometry of different conformers of the compounds were optimised with B3LYP and B3PW91 methods using 6-311++G and aug-cc-pVTZ basis sets to characterise all stationary points as minima. The optimised structural parameters of the most stable conformer were used in the vibrational frequency calculations. The Raman activities were also determined with B3LYP method using 6-311++G basis sets. The force constants obtained from the B3LYP/6-311++G method have been utilised in the normal coordinate analysis. The temperature dependence of the thermodynamic properties heat capacity at constant pressure (C(p)), entropy (S) and enthalpy change (ΔH(0→T)) for both the compounds were also determined by B3LYP/6-311++G method. The total electron density and MESP surfaces of the molecules were constructed by NBO analysis using B3LYP/6-311++G method to display electrostatic potential (electron+nuclei) distribution, molecular shape, size, and dipole moments of the molecule. The electronic properties HOMO and LUMO energies were measured. The influences of nitro and methyl groups on the skeletal modes have been investigated.

1-Methyl-5-nitro-1H-imidazole

In the title compound, C(4)H(5)N(3)O(2), the nitro group is twisted with respect to the imidazole ring by a dihedral angle of 5.60 (2)°. Weak inter-molecular C-H⋯O and C-H⋯N hydrogen bonding is present in the crystal structure.

A DFT study of aminonitroimidazoles

Density functional theory (DFT) calculations at the B3LYP/aug-cc-pVDZ level were performed to explore the geometric and electronic structures, band gaps, thermodynamic properties, densities and performances of aminonitroimidazoles. The calculated performance properties, stabilities and sensitivities of the model compounds appear to be promising compared with those of the known explosives 2,4-dinitro-1H-imidazole (2,4-DNI), 1-methyl-2,4,5-trinitroimidazole (MTNI), hexahydro-1,3,5-trinitro-1,3,5-triazinane (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocane (HMX). The position of the NH(2) or the number of NO(2) groups on the diazole presumably determines the structure, heat of formation, stability, sensitivity, density and performance of the compound.

Trinitromethyl-substituted 5-nitro- or 3-azo-1,2,4-triazoles: synthesis, characterization, and energetic properties

Various new polynitro-1,2,4-triazoles containing a trinitromethyl group were synthesized by straightforward routes. These high nitrogen and oxygen-rich compounds were fully characterized using IR and multinuclear NMR spectroscopy, elemental analysis, natural bonding orbital (NBO) analysis, and differential scanning calorimetry (DSC) and, in the case of 12, with single crystal X-ray structuring. The heats of formation for all compounds were calculated with Gaussian 03 (revision D.01) and then combined with experimentally determined densities to determine detonation pressures (P) and velocities (D) of the energetic materials (Cheetah 5.0). They exhibit high density, good thermal stability, acceptable oxygen balance, positive heat of formation, and excellent detonation properties, which, in some cases, are superior to those of TNT, RDX, and HMX.

Computational design and structure-property relationship studies on heptazines

This study aimed to design novel nitrogen-rich heptazine derivatives as high energy density materials (HEDM) by exploiting systematic structure-property relationships. Molecular structures with diverse energetic substituents at varying positions in the basic heptazine ring were designed. Density functional techniques were used for prediction of gas phase heat of formation by employing an isodesmic approach, while crystal density was assessed by packing calculations. The results reveal that nitro derivatives of heptazine possess a high heat of formation and further enhancement was achieved by the substitution of nitro heterocycles. The crystal packing density of the designed compounds varied from 1.8 to 2 g cm(-3), and hence, of all the designed molecules, nitro derivatives of heptazine exhibit better energetic performance characteristics in terms of detonation velocity and pressure. The calculated band gap of the designed molecules was analyzed to establish sensitivity correlations, and the results reveal that, in general, amino derivatives possess better insensitivity characteristics. The overall performance of the designed compounds was moderate, and such compounds may find potential applications in gas generators and smoke-free pyrotechnic fuels as they are rich in nitrogen content.

Computational study of imidazole derivative as high energetic materials

Density functional theory (DFT) calculations were performed for a series of imidazole derivatives. B3LYP and B3P86 functionals with 6-31G** basis set were used. Heats of formation (HOFs) were predicted through designed isodesmic reactions. Calculated results show that the HOFs relate to the number and the position of nitro groups. The HOFs increase with the augment of the number of the NO(2) group for the direct imidazole derivatives and decrease with the augment of the number of the NO(2) group for 1-picrylimidazole derivatives. Thermal stabilities were evaluated via bond dissociation energies (BDEs). The result shows that the increase of nitro group number on imidazole ring reduces the stability of the molecule. Further, the correlation was developed between impact sensitivity h(50) and the ratio (BDE/E) of the weakest bond BDE to the total energy E. The detonation performance data were also calculated.

Potent and cellularly active 4-aminoimidazole inhibitors of cyclin-dependent kinase 5/p25 for the treatment of Alzheimer's disease

Utilizing structure-based drug design, a 4-aminoimidazole heterocyclic core was synthesized as a replacement for a 2-aminothiazole due to potential metabolically mediated toxicity. The synthetic route utilized allowed for ready synthesis of 1-substituted-4-aminoimidazoles. SAR exploration resulted in the identification of a novel cis-substituted cyclobutyl group that gave improved enzyme and cellular potency against cdk5/p25 with up to 30-fold selectivity over cdk2/cyclin E.

Quantum chemical study on nitroimidazole, polynitroimidazole and their methyl derivatives

The insensitive explosive candidates, nitroimidazoles, polynitroimidazoles and their methyl derivatives, are investigated using density functional theory (DFT). The homolytic bond dissociation energies (BDEs) corresponding to -NO2 group removal from carbon or nitrogen site on imidazole ring were calculated at B3P86/6-311G** level, and the weakest bond has been determined. Further, a correlation is developed between impact sensitivity h50 and the ratio (BDE/E) of the weakest bond BDE to the total energy E, and we extrapolate this relationship to predict the impact sensitivities for compounds where experiments are not available. It is found that most of the title compounds are insensitive towards impact stimuli with their h50 larger than 60.0cm. Heats of formation (HOFs) for the 21 title compounds at 298K in gas are also determined both at B3LYP/6-311G** and B3P86/6-311G** levels using isodesmic work reactions. The calculated BDEs and HOFs consistently indicate that C-nitro-substituted imdazole is more stable than the corresponding N-substituted one, and the introduction of methyl on C increases the stability whereas the methyl attached to N atom decreases the stability.

Advances in science and technology of modern energetic materials: an overview

Energetic materials such as explosives, propellants and pyrotechnics are widely used for both civilian and military explosives applications. The present review focuses briefly on the synthesis aspects and some of the physico-chemical properties of energetic materials of the class: (a) aminopyridine-N-oxides, (b) energetic azides, (c) high nitrogen content energetic materials, (d) imidazoles, (e) insensitive energetic materials, (f) oxidizers, (g) nitramines, (h) nitrate esters and (i) thermally stable explosives. A brief comment is also made on the emerging nitration concepts. This paper also reviews work done on primary explosives of current and futuristic interest based on energetic co-ordination compounds. Lead-free co-ordination compounds are the candidates of tomorrow's choice in view of their additional advantage of being eco-friendly. Another desirable attribute of lead free class of energetic compounds is the presence of almost equivalent quantity of fuel and oxidizer moieties. These compounds may find wide spectrum of futuristic applications in the area of energetic materials. The over all aim of the high energy materials research community is to develop the more powerful energetic materials/explosive formulations/propellant formulations in comparison to currently known benchmark materials/compositions. Therefore, an attempt is also made to highlight the important contributions made by the various researchers in the frontier areas energetic ballistic modifiers, energetic binders and energetic plasticizers.

Synthesis, characterization and thermolysis studies on new derivatives of 2,4,5-trinitroimidazoles: potential insensitive high energy materials

This paper reports the synthesis of three new derivatives of 2,4,5-trinitroimidazole namely, 1-methyl-2,4,5-trinitroimidazole (III), 1-carboethoxy-2,4,5-trinitroimidazole (V) and 1-picryl-2,4,5-trinitroimidazole (VII). The title compounds (III) and (V) were synthesized by the nitration of 1-methyl-/1-carboethoxy-(2,4,5-triiodoimidazole) (II and IV) with fuming nitric acid at 0 degrees C and (VII) was synthesized by condensation of 2,4,5-triiodoimidazole (I) with picryl chloride to obtain 1-picryl-2,4,5-triiodoimidazole (VI) followed by its nitration with fuming nitric acid at 0 degrees C. The synthesized compounds have been characterized by elemental analysis, spectral and thermal techniques. The thermolysis studies using TG-DTA revealed exothermic decomposition of the nitroimidazoles (III, V and VII) with T(max) in the temperature range of 196-225 degrees C. The energy of activation obtained for these compounds was in the range 150-170 kJ/mol. The sensitivity data obtained for the newly synthesized compounds (III, V and VII) indicated their safe nature towards external stimuli (h(50%)>100 cm; friction>36 kg) and could be potential candidates for low vulnerable applications in the futuristic systems. The theoretically predicted performance parameters suggest that 1-methyl-2,4,5-trinitroimidazole (III), exhibits higher velocity of detonation (VOD: 8.8 km/s) compared to compounds V and VII (VOD: 7.6 and 8.41 km/s, respectively).

2,4,5-Trinitroimidazole-Based Energetic Salts

2,4,5-Trinitroimidazolate (TNI) salts with "high-nitrogen" cations tend to be highly hydrogen bonded and have heats of formation ranging up to 616 kJ mol(-1). Density, oxygen balance, and thermostability are enhanced by the presence of TNI. Based on theoretical calculations, all of the new salts are potential propellants.

In Search of Ionic Liquids Incorporating Azolate Anions

Twenty-eight novel salts with tetramethyl-, tetraethyl-, and tetrabutylammonium and 1-butyl-3-methylimidazolium cations paired with 3,5-dinitro-1,2,4-triazolate, 4-nitro-1,2,3-triazolate, 2,4-dinitroimidazolate, 4,5-dinitroimidazolate, 4,5-dicyanoimidazolate, 4-nitroimidazolate, and tetrazolate anions have been prepared and characterized by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and single-crystal X-ray crystallography. The effects of cation and anion type and structure on the physicochemical properties of the resulting salts, including several ionic liquids, have been examined and discussed. Ionic liquids (defined as having m.p.<100 degrees C) were obtained with all combinations of the 1-butyl-3-methylimidazolium cation ([C(4)mim](+)) and the heterocyclic azolate anions studied, and with several combinations of tetraethyl or tetrabutylammonium cations and the azolate anions. The [C(4)mim](+) azolates were liquid at room temperature exhibiting large liquid ranges and forming glasses on cooling with glass-transition temperatures in the range of -53 to -82 degrees C (except for the 3,5-dinitro-1,2,4-triazolate salt with m.p. 33 degrees C). Six crystal structures of the corresponding tetraalkylammonium salts were determined and the effects of changes to the cations and anions on the packing of the structure have been investigated.

Stereoselective synthesis of cis-1,3-disubstituted cyclobutyl kinase inhibitors

Two synthetic routes to a series of structurally novel kinase inhibitors containing a cis-1,3-disubstituted cyclobutane are described. The first route utilized addition of 3-aminocyclobutanol to 1,4-dinitroimidazole 5 as the crucial step in preparing 1, whereas the second route employed a novel 1,4-addition of 4-nitroimidazole 18 to in situ generated cyclobutenone 17 as the key reaction. This allowed for a stereoselective and shorter synthesis that eliminated the use of potentially explosive 1,4-dinitroimidazole 5. [structure: see text]