Relationship between the Bond Dissociation Energies and Impact Sensitivities of Some Nitro‐Explosives

The bond dissociation energy (BDE) for removal of the NO₂ group for eleven CHNO nitro‐containing explosive molecules is studied to find its correlation with impact sensitivity. The BDE for removal of the NO₂ group in nitroaromatic molecules with nitro alkyl, and esters with nitro alkyl, is calculated using the B3LYP method of Density Functional Theory with the 6‐31G* basis set. The relationship between the impact sensitivities and the weakest C‐NO₂ bond dissociation energy values is examined. The results indicate a nearly linear correlation between the impact sensitivity and the ratio of the BDE value to the total molecular energy.     

Calculation of Detonation Velocity,Pressure, and Electric Sensitivity of Nitro Arenes Based on Quantum Chemistry

The DFT‐B3LYP method, with basis set 6‐31G*, is employed to optimize molecular geometries and electronic structures of thirty‐nine nitro arenes. The averaged molar volume (V) and theoretical density (ϱ) are estimated using the Monte‐Carlo method, based on 0.001 electrons/bohr³ density space and a self‐compiled program. The detonation velocity (D) and pressure (P) of the explosives are estimated by using the Kamlet–Jacbos equation on the basis of the theoretical density and heat of formation (Δ_fH), which is calculated using the PM3 method. The reliability of this theoretical method and results are tested by comparing the theoretical values of ϱ and D with the experimental or referenced values. The theoretical values of D and P are correlated with the experimental values of electric sensitivity (E_ES). It is found that, for the nitro arenes, there is a linear relationship between the square of detonation velocity (D²) or detonation pressure (P) and electric sensitivity (E_ES), which suggests that such a theoretical approach can be used to predict or judge the magnitude of E_ES, which is difficult to measure in the molecular design of energetic materials. In addition, we have discussed the influence of the substituted groups and the parameters of the electronic structure on density, detonation velocity, pressure, and electric sensitivity, and have shown that the substituted groups have the effect of activity or insensitivity, and that the influence of Q_‐NO2 and E_LUMO is important.     

Computational Studies on Nitro,Nitramino, and Dinitramino Derivatives of 1‐Aminoazadiboridine as High Energetic Material

Computational studies were performed to determine the thermodynamic and explosive characteristics of high energy materials formed by placing explosophores such as nitro (−NO₂), nitramino (−NHNO₂), and dinitramino (−N(NO₂)₂) groups on 1‐aminoazadiboridine. G3 level calculations were made to determine the gas phase heat of formation of the designed species. In addition to the above, condensed phase heat of formation was also determined by evaluating the sublimation enthalpy. Crystal densities of title compounds were predicted with the help of a wave function analysis (WFA) program and were found to be in the range of 1.55–1.83 g cm⁻³. Bond dissociation energies of various possible bond rupture routes of the designed molecules were calculated at DFT‐B3LYP/6‐311G(d,p) level and attempt was made to identify the trigger linkage. Impact sensitivity was evaluated theoretically by employing a method based on statistical parameters determined from electrostatic potential data. Results show that the designed molecules are highly energetic and their corresponding detonation properties place them in the category of safe and high performance explosive materials.     

Theoretical Screening of Novel 5-picrylamino- 1,2,3,4-tetrazole (PAT) and 5,5′-styphnylamino-1,2,3,4-tetrazole (SAT) Derivatives: A New Molecular Design Strategy of Multi-Nitrogen Energetic Materials by Introducing Intermolecular Hydrogen Bonds and π–π Stacking Interactions

On the basis of a design strategy that results in the introduction of intramolecular hydrogen-bonds and π–π stacking interactions leading to low-sensitive and high-energy materials (LSHMs), –NH₂/–NO₂ fused derivatives of 5-picrylamino- 1,2,3,4-tetrazole (PAT) and 5,5′-styphnylamino- 1,2,3,4-tetrazole (SAT) were designed and investigated theoretically. Density functional theory has been explored to investigate the geometric, electronic structures, band gaps, and heats of formation. The detonation performance was evaluated by using Kamlet-Jacobs equations based on the calculated densities and enthalpy of formation (EOF). The thermal stability of these compounds was studied by calculating bond dissociation energies and energy gaps. Proper numbers of 5-aminotetrazole (5-AT) moieties can enhance the EOFs of explosives, further improving the detonation performance as well as nitro group. Though introducing more nitro-groups into TATB frameworks, NH-moieties can retain the intramolecular hydrogen-bond, which can enhance the crystal-packing and physico-chemical stability. Meanwhile, noncovalent interaction (NCI) plots reflects that intermolecular interaction also has a crucial influence on the mechanical sensitivity for the designed derivatives, except for the energy gap (ΔE) and bond dissociation energy (BDE). UV/Vis spectra and ¹⁵N isotropic magnetic shielding were further computed for characterizing and predicting the molecular structure and reaction mechanism towards the future experiments. The predicted performance implies that the designed molecules are expected to be promising candidates for multi-nitrogen energetic materials.     

Review on Greener and Safer Synthesis of Nitro Compounds

The review describes the recent developments in the green synthetic methods of nitro compounds involving environmentally benign approaches such as, use of solid‐supported reagents, microwave‐assisted reactions, ionic liquids, ultrasound assisted nitration reactions, gas phase nitration and vapor phase nitration.     

Effect of Nitrogen‐Doping on Detonation and Stability Properties of CL‐20 Derivatives from a Theoretical Viewpoint

Six nitrogen‐doping CL‐20 derivatives were designed and investigated as energetic materials at B3LYP/6‐31G** level based on the density functional theory method. Results show that nitrogen‐doping derivatives exhibit high crystal densities (1.98∼2.18 g cm⁻³) and positive heats of formation (451.68∼949.68 kJ mol⁻¹). Among nitrogen‐doping derivatives, 2,4,6,8,10,12‐hexanitro‐2,4,6,8,9,10,12‐heptaazaisowurtzitane(A1), 2,4,6,8,10,12‐hexanitro‐2,3,4,6,8,9,10,12‐octaazaisowurtzitane(B1) and 2,4,6,8,10,12‐hexanitro‐1,2,3,4,6,8,9,10,12‐nonaazaisowurtzitane(C1) possess better detonation velocity and pressure than CL‐20, and A1 gives the best performance (D _K‐J•A1=9.6 km s⁻¹; P _K‐J•A1=43.07 GPa). Moreover, the specific impulse, brisance, and power of N‐doping CL‐20 derivatives are also higher than that of CL‐20. The thermal stability and sensitivity of nitrogen‐doping molecules were analyzed via the bond dissociation energy (BDE ), the characteristic height (h₅₀) and electrostatic sensitivity (E _ES). The results indicate that the stability of A1, B1 and 2,4,6,8,10,12‐hexanitro‐1,2,3,4,6,7,8,9,10,12‐decaazaisowurtzitane(D1) is comparable with that of CL‐20. Considering detonation performance and stability, A1 and B1 may be promising candidates as energetic materials with superior detonation performance and favorable stability.     

Single Step Synthesis of Nitro‐Functionalized Hydroxyl‐Terminated Polybutadiene

The paper reports the energization of Hydroxyl‐Terminated Polybutadiene (HTPB) by functionalizing explosophore  NO₂ over the HTPB backbone, resulting in the formation of conjugated nitro‐alkene derivative of HTPB. A convenient, inexpensive and efficient “one pot” procedure of synthesizing Nitro‐Functionalized Hydroxyl‐Terminated Polybutadiene (Nitro‐HTPB) is reported. The reaction was carried out with sodium nitrite and iodine. To retain the unique physico‐chemical properties of HTPB, functionalization by  NO₂ group was restricted to 10 to 15 % of double bonds. The Nitro‐HTPB was characterized by FTIR, ¹H NMR, VPO, DSC, TGA etc. The polymer has shown good thermal stability for practical applications. The kinetic parameters for the decomposition of Nitro‐HTPB at 150–300 °C were obtained from non‐isothermal DSC data.     

Thermal Decomposition of NTO: An Explanation of the High Activation Energy

Burning rate characteristics of the low‐sensitivity explosive 5‐nitro‐1,2,4‐triazol‐3‐one (NTO) have been investigated in the pressure interval of 0.1–40 MPa. The temperature distribution in the combustion wave of NTO has been measured at pressures of 0.4–2.1 MPa. Based on burning rate and thermocouple measurements, rate constants of NTO decomposition in the molten layer at 370–425 °C have been derived from a condensed‐phase combustion model (k=8.08⋅10¹³⋅exp(−19420/T) s⁻¹. NTO vapor pressure above the liquid (ln P=−9914.4/T+14.82) and solid phases (ln P=−12984.4/T+20.48) has been calculated. Decomposition rates of NTO at low temperatures have been defined more exactly and it has been shown that in the interval of 180–230 °C the decomposition of solid NTO is described by the following expression: k=2.9⋅10¹²⋅exp(−20680/T). Taking into account the vapor pressure data obtained, the decomposition of NTO in the gas phase at 240–250 °C has been studied. Decomposition rate constants in the gaseous phase have been found to be comparable with rate constants in the solid state. Therefore, a partial decomposition in the gas cannot substantially increase the total rate. High values of the activation energy for solid‐state decomposition of NTO are not likely to be connected with a sub‐melting effect, because decomposition occurs at temperatures well below the melting point. It has been suggested that the abnormally high activation energy in the interval of 230–270 °C is a consequence of peculiarities of the NTO transitional process rather than strong bonds in the molecule. In this area, the NTO molecule undergoes isomerization into the aci‐form, followed by C3‐N2 heterocyclic bond rupture. Both processes depend on temperature, resulting in an abnormally high value of the observed activation energy.     

Novel Melt‐Castable Energetic Pyrazole: A Pyrazolyl‐Furazan Framework Bearing Five Nitro Groups

Continuing advances in energetic pyrazole construction foster further its rational use. This work establishes an approach for the first synthesis of nitropyrazole that bear both furazan and trinitromethyl moieties. The approach to the installation of the C(NO₂)₃ group exploits the destructive nitration of N‐acetonyl group. The target 3‐(3,4‐dinitro‐1‐(trinitromethyl)‐1H‐pyrazol‐5‐yl)‐4‐methylfurazan ( 6 ) has promising explosive properties.     

Study of the microwave dielectric properties of (La1−xSmx)NbO4 (x=0‐0.10) ceramics via bond valence and packing fraction

The (La_1?xSm_x)NbO₄ (x=0‐0.10) ceramics were prepared by the conventional solid‐state reaction method. The microstructure and the microwave dielectric properties were discussed in detail. The X‐ray diffraction patterns of (La_1?xSm_x)NbO₄ (x=0‐0.10) showed that only a single monoclinic fergusonite structure of LaNbO₄ could be found. The dielectric constant (ε_r) was affected by the dielectric polarizabilities and the B‐site bond valence. The variation trend of Q×f₀ was in accordance with packing fraction. The temperature coefficient of resonant frequency (τ_f) had a close relationship with the B‐site bond valence, which was determined by the bond strength and bond length. When sintered at 1325°C for 4 hours, the (La_1?xSm_x)NbO₄ ceramics with x=0.08 exhibited enhanced microwave dielectric properties: ε_r=19.37, Q×f₀=62203 GHz and τ_f=2.57 ppm/°C. In addition, we made an overview about the ceramics that possess the same packing fraction and bond valence relationships, the results show that this structure‐property relationship has a wide applicability.     

Computed Thermodynamic and Explosive Properties of 1‐Azido‐2‐nitro‐2‐azapropane (ANAP)

Some thermodynamic and explosive properties of the recently reported 1‐azido‐2‐nitro‐2‐azapropane (ANAP) have been determined in a combined computational ab initio (MP2/aug‐cc‐pVDZ) and EXPLO5 (Becker–Kistiakowsky–Wilson's equation of state, BKW EOS) study. The enthalpy of formation of ANAP in the liquid phase was calculated to be Δ_fH°, ANAP(l)=+297.1 kJ mol⁻¹. The heat of detonation (Q_v), the detonation pressure (P), and the detonation velocity of ANAP were calculated to be Q_v=−6088 kJ kg⁻¹, P=23.8 GPa, D=8033 m s⁻¹. A mixture of ANAP and tetranitromethane (TNM) was investigated in an attempt to tailor the impact sensitivity of ANAP, but results obtained indicate that the mixture is almost as sensitive as pure ANAP. On the other hand, ANAP and TNM were found to be chemically compatible (¹H, ¹³C, ¹⁴N NMR; DSC) and a 1 : 1 mixture (by weight) of both components was calculated to have superior explosive properties than either of the individual components: Q_v=−6848 kJ kg⁻¹, P=27.0 GPa, D=8284 m s⁻¹.     

Synthesis and Microwave Dielectric Properties of Cu‐Doped ZnAl2O4

Spinel materials of composition Zn_1?xCu_xAl₂O₄ (ZCA, x = 0–0.015) were prepared via the conventional solid‐state route. The lattice structure, microstructure, and microwave dielectric properties were investigated as a function of Cu content. Cu doping was found to improve the sinterability and, meanwhile, significantly increase the quality factor (Q × f₀), which is due to the Cu‐O bond is stronger than Zn‐O bond, and inhibit the oxygen vacancy considered to be responsible for the enhanced Q × f₀ value of ZCA materials. The best microwave dielectric properties were obtained in Zn_0.99Cu_0.01Al₂O₄ with ε_r = 8.69, Q × f₀ = 69,300 GHz and τ_f = ?58.3 ppm/°C, which was sintered at 1520°C for 3 h in air.     

Nitro derivatives of PEEK‐WC

Nitrated poly(oxa‐p‐phenylene‐3,3‐phthalido‐p‐phenylene‐oxa‐p‐phenylene‐ oxy‐phenylene) (PEEK‐WC) with various average degrees of substitution was obtained by reaction with several nitrating agents. By working under controlled reaction conditions, little degradation of the parent polymer is observed. The nitro derivatives of PEEK‐WC show a high thermal stability, and are able to form membranes by means of phase inversion technique. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1037–1045, 2001     

Synthesis,Characterization and Properties of Nitropolybutadiene as Energetic Plasticizer for NHTPB Binder

The nitration of low molecular weight polybutadiene (PB) by a convenient and inexpensive procedure was investigated. To retain the unique physico‐chemical properties of the plasticizer, it was nitrated to an extent of 10 % double bonds. The product nitropolybutadiene (NPB) was characterized by FT‐IR and ¹H NMR spectroscopy as well as GPC, DSC, and TGA methods. The kinetic parameters for the decomposition of NPB from room temperature to 400 °C were obtained from non‐isothermal DSC. The changes in glass transition temperature (T _g) and inert uncured binder systems were used for determination of its efficiency as plasticizer. NPB was used in cured and unfilled nitro‐hydroxyl terminated polybutadiene (NHTPB) binder. Isothermal thermogravimetric analysis (Iso‐TGA) was employed to determine the migration rate in cured and unfilled HTPB binder systems compared to the dioctyladiphate (DOA) plasticizer. It was found that the exudation of the NPB plasticizer is slower than that of the DOA plasticizer. Thus, the NHTPB/NPB binder system (binder/plasticizer) presents more convenient mechanical properties than HTPB/DOA and is a promising new energetic binder system for polymer bonded explosives.     

Study of the Heat and Kinetics of Nitration of 1,2,4‐Triazol‐5‐one (TO)

The heat effects of the nitration and dissolution processes of 1,2,4‐triazol‐5‐one (TO) in acidic environments were measured by differential reaction calorimetry. The kinetics of nitration of TO in a 200‐mL reactor were investigated by UV/Vis spectroscopy. Temperature changes were measured in a 10‐L batch reactor during the TO nitration. A model of kinetics for the synthesis of 3‐nitro‐1,2,4‐triazol‐5‐one (NTO) was proposed and it was used to simulate the phenomena occurring in the calorimeter and in the reactors. The experimental data were compared with modeling results and parameters of the Arrhenius equation for synthesis of NTO with selected nitration mixtures were determined.     

Investigations about the Reducing Properties of Dimeric Dihydropyridines

The reaction of a series of bis-[1,4-dihydropyridinyl-(4)] derivatives P₂ with some benzyl halides, trans-1,2-dibromoethane and several heteroaromatic cations Q^⊕ was investigated in acetonitrile/toluene with electrochemical and kinetic methods. For substrates with a reduction potential between −0.9 and −1.5 V the reaction occurs via the ratedetermining dissociation of P₂ into free radicals P^. as the real reducing agents, which transform the benzyl halides into the corresponding 1,2-diarylethanes and Q^⊕ into the corresponding dimeric product Q₂. For the reduction of trans-1,2-dibromocyclohexane to cyclohexene a simultaneous transfer of two electrons to the substrate combined with the dissociation of P₂ into two pyridinium ions P^⊕ is proposed. In the case of a reduction potential more positive than −0.9 V (e.g. nitro substituted benzyl halides) P₂ itself can act as the reducing agent with an increased reaction rate. With pyrylium ions Q^⊕ a product P-Q was detected by voltammetry and mass spectroscopy. In this case an electrophilic attack onto P₂ instead of the electron transfer from P₂ to Q^⊕ cannot be excluded.     

Preparation of organo‐soluble poly[(2,2′‐m‐phenylene)‐5,5′‐bibenzimidazole] with high yield by homogeneous nitration reaction

To prepare organo‐soluble poly[(2,2,′‐m‐phenylene)‐5,5′‐bibenzimidazole] (PBI) with high yield, a homogeneous nitration of PBI was attempted. Nitro‐substituted PBI (NO₂‐PBI) was synthesized through the homogeneous reaction of the PBI powder with nitric acid in sulfuric acid. The degree of substitution (DS) of this NO₂‐PBI is higher than that of the NO₂‐PBI prepared through the heterogeneous reaction of the PBI fiber. The viscosity of the NO₂‐PBI prepared through the homogeneous reaction decreased with increasing amount of nitric acid added. The DS of the NO₂‐PBI reached the maximum value of 2. The substitution efficiency of nitro groups decreased as the amount of nitric acid added increased. When a small quantity of nitric acid was added, the substitution of the sulfonic acid group was confirmed as well as that of the nitro group. The solubility of the NO₂‐PBI depended strongly on the DS. The NO₂‐PBI having the DS of about 2 was completely soluble in dimethylacetamide and almost soluble in N‐methylpyrrolidone. At an elevated temperature, it was also soluble in other polar aprotic solvents such as dimethylformamide and dimethylsulfoxide. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 438–445, 2000     

Nitro radical anions from megazol and related nitroimidazoles in aprotic media. A father-son type reaction triggered by an acidic proton

We have studied the electrochemical reduction of some nitroimidazoles such as megazol(2-amino-5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4-thiadiazol, CAS 19622-55-0) and two related derivatives in aprotic media (100% DMF, 0.1 M TBAP). All the studied compounds were easily reducible in aprotic media generating the corresponding nitro radical anions as products of the one electron reduction of the parent compound. The nitro radical anions decay by a dimerization reaction and the dimerization rate constants were obtained according to the Olmstead's approach by obtaining values of 150±24, 1690±42 and 640±32 M⁻¹ s⁻¹ for megazol, GC-361 and GC-284, respectively. The existence of an acidic proton on the acetamide group in the GC-361 molecule triggered the appearance of father-son type reactions between the nitro radical anion from GC-361 (son compound) and GC-361 (father compound) generating the neutral radical and the conjugate base of GC-361. Thus the nitro radical anion from GC-361 acts as a Brönsted base abstracting the proton of the acetamide group in the GC-361 derivative of megazol.     

Directional Interactions of α‐Particles with FOX‐7. A DFT Study

FOX‐7 is exposed to the effects of α‐particles from selected directions of approach. Various energies and properties of these composite FOX‐7 systems (FOX‐7+α‐particle) are obtained. The effect of α‐particles on FOX‐7 is drastic. The CC double bond turns into a single bond and one of the C NO₂ bonds highly elongates. The approach from the side of amino groups results more stable composite system compared to the approach from the side of nitro groups.     

Discovery and characterization of atropisomer PH-797804, a p38 MAP kinase inhibitor, as a clinical drug candidate

PH‐797804 ((aS)‐3‐{3‐bromo‐4‐[(2,4‐difluorobenzyl)oxy]‐6‐methyl‐2‐oxopyridin‐1(2H)‐yl}‐N,4‐dimethylbenzamde) is a diarylpyridinone inhibitor of p38 mitogen‐activated protein (MAP) kinase derived from a racemic mixture as the more potent atropisomer (aS), first proposed by molecular modeling and subsequently confirmed by experiments. Due to steric constraints imposed by the pyridinone carbonyl group and the 6‐ and 6′‐methyl substituents of PH‐797804, rotation around the connecting bond of the pyridinone and the N‐phenyl ring is restricted. Density functional theory predicts a remarkably high rotational energy barrier of >30 kcal mol^?1, corresponding to a half‐life of more than one hundred years at room temperature. This gives rise to discrete conformational spaces for the N‐phenylpyridinone group, and as a result, two atropic isomers that do not interconvert under ambient conditions. Molecular modeling studies predict that the two isomers should differ in their binding affinity for p38α kinase; whereas the atropic S (aS) isomer binds favorably, the opposite aR isomer incurs significant steric interference with p38α kinase. The two isomers were subsequently identified and separated by chiral chromatography. IC₅₀ values from p38α kinase assays confirm that one atropisomer is >100‐fold more potent than the other. It was ultimately confirmed by small‐molecule X‐ray diffraction that the more potent atropisomer, PH‐797804, is the aS isomer of the racemic pair. Extensive pharmacological characterization supports that PH‐797804 carries most activity both in vitro and in vivo, and it has a stability profile compatible with oral formulation and delivery options.