Cyclic Nitramines Research Articles

Comparative theoretical studies of high energetic cyclic nitramines

Density functional theory studies on cyclic nitramines were performed at B3LYP/6‐311G(d,p) level. The crystal structures were obtained by molecular packing calculations. Heats of formation (HOFs) were predicted through designed isodesmic reactions. Results indicate that the value of HOF relates to the number of =N–NO2 group and aza nitrogen atom and increases with the augment of the number of =N–NO2 group and aza nitrogen atom for cyclic nitramines. Detonation performance was evaluated by using the Kamlet–Jacobs equations based on the calculated densities and HOFs. All the cyclic nitramines exhibit better detonation performance than 1,3,5‐trinitro‐1,3,5‐triazacyclohexane and 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane. The stability of cyclic nitramines was investigated by the bond dissociation energies. The result shows that the increase of =N−NO2 group or aza nitrogen atom reduces the stability of the title compounds. These results provide basic information for molecular design of novel high energetic density materials. Copyright © 2013 John Wiley & Sons, Ltd.

Predicting the heats of combustion of polynitro arene, polynitro heteroarene, acyclic and cyclic nitramine, nitrate ester and nitroaliphatic compounds using bee algorithm and adaptive neuro-fuzzy inference system

A new method was developed for prediction of the heats of combustion of important classes of energetic compounds including polynitro arene, polynitro heteroarene, acyclic and cyclic nitramine, nitrate ester and nitroaliphatic compounds. A set of 1497 zero- to three-dimensional descriptors was generated for each molecule in the data set. A major problem of modeling is the high dimensionality of the descriptor space; therefore, descriptor selection is one of the most important steps. In this paper, bee algorithm (BA) was used to select the best descriptors. Bee algorithm is a new population-based optimization algorithm, which is derived from the observation of real bees and proposed to feature selection. Four descriptors were selected and used as inputs for adaptive neuro-fuzzy inference system (ANFIS). Squared correlations of coefficients were obtained as 0.9980, 0.9996 and 0.9988 for training, test and validation sets, respectively. In comparison with genetic algorithm (GA)-ANFIS and multiple linear regression (MLR)-ANFIS, the results showed that Bee-ANFIS can be used as a powerful model for prediction of heats of combustion of these compounds.

Improved Approach to Predict the Power of Energetic Materials

AbstractNowadays, the ballistic mortar is the preferred test for the explosive power measurements but there is no reliable method for its prediction. For an energetic compound, the formation of low molecular mass gaseous products and a high positive heat of formation per unit weight of the energetic compound are important parameters to have a high value of power. A novel method was developed to predict the power by the ballistic mortar test for pure and mixture of energetic materials. It can be used for some important classes of energetic compounds including nitroaromatics, acyclic and cyclic nitramines, nitrate esters, and nitroaliphatics. The presented method is based on the molecular structure of the desired compound and there is no need to use experimental data such as the condensed phase heat of formation. For 84 pure and 24 mixtures of energetic compounds, the calculated power relative to 2,4,6‐trinitrotoluene (= 100) show good agreement with respect to the measured values.

Thermal behavior and decomposition kinetics of Viton A bonded explosives containing attractive cyclic nitramines

The thermal behavior and decomposition kinetics of Viton A bonded PBXs containing some attractive cyclic nitramines were investigated by means of nonisothermal TG and DSC techniques. It has been shown that only a single decomposition process has been observed for RDX-VA, CL-20-VA and HMX-VA while an obvious two-step process for BCHMX-VA under 1.0°Cmin−1. The exothermic onset temperatures of RDX-VA, BCHMX-VA, HMX-VA and CL-20-VA were found as 212.6, 241.3, 277.6 and 237.8°C with the peak maximum of 234.1, 242.6, 278.7 and 238.6°C, respectively. Their corresponding heat releases were determined as 1552, 1263, 1302 and 1597Jg−1, which are much lower than that of the pure cyclic nitramines. It has been proved that Formex polymer is not good binder for BCHMX, while Viton A is better than C4 and Formex as the binder of cyclic nitramines for the sake of greater thermal stability. Viton A has a significant effect on the activation energy distribution of cyclic nitramines, and the initial autocatalysis effect for RDX and BCHMX was weakened or inhibited. The activation energies for thermolysis of RDX-VA, BCHMX-VA, HMX-VA and CL-20-VA were found almost independent on the extent of conversion at interval of 0.3–0.7 with the mean values of 174.4±3.1, 183.3±1.3, 285.8±11.7 and 184.0±4.3kJmol−1, respectively.

Surface-Accelerated Decomposition of δ-HMX.

Despite extensive efforts to study the explosive decomposition of HMX, a cyclic nitramine widely used as a solid fuel, explosive, and propellant, an understanding of the physicochemical processes, governing the sensitivity of condensed HMX to detonation initiation is not yet achieved. Experimental and theoretical explorations of the initiation of chemistry are equally challenging because of many complex parallel processes, including the β-δ phase transition and the decomposition from both phases. Among four known polymorphs, HMX is produced in the most stable β-phase, which transforms into the most reactive δ-phase under heat or pressure. In this study, the homolytic NO2 loss and HONO elimination precursor reactions of the gas-phase, ideal crystal, and the (100) surface of δ-HMX are explored by first principles modeling. Our calculations revealed that the high sensitivity of δ-HMX is attributed to interactions of surfaces and molecular dipole moments. While both decomposition reactions coexist, the exothermic HONO-isomer formation catalyzes the N-NO2 homolysis, leading to fast violent explosions.

Noniso-thermal analysis of C4 bonded explosives containing different cyclic nitramines

The thermal behavior and decomposition kinetics of C4-bonded PBXs based on some attractive cyclic nitramines were investigated by means of nonisothermal TG and DSC techniques. It has been shown that only a single decomposition process has been observed for RDX-C4 while an obvious two-step process for mixture of BCHMX-C4 CL-20-C4, and HMX-C4. The onset temperature of the exotherms were observed at 216.3, 238.7, 279.2 and 236.7°C with the peak temperatures of 235.1, 279.0, 231.2 and 233.7°C for RDX-C4, BCHMX-C4, HMX-C4 and CL-20-C4, respectively. Their corresponding exothermic decompostion processes were covered by energy changes of 1749, 1938, 1213 and 2639Jg−1, which are lower than that of their pure cyclic nitramines. It was also proved that C4 matrix has significant effect on the activation energy distribution of RDX, BCHMX and CL-20, whose initial autocatalysis effect was inhibited or weakened. With regard to HMX-C4, the activation energy of its initial step is much lower than that of the second step.

Study of Plastic Explosives based on Attractive Cyclic Nitramines, Part II. Detonation Characteristics of Explosives with Polyfluorinated Binders

AbstractA series of plastic bonded explosives (PBXs) based on Viton A and Fluorel binders were prepared using four nitramines, namely RDX (1,3,5‐trinitro‐1,3,5‐triazinane), β‐HMX (β‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane), BCHMX (cis‐1,3,4,6‐tetranitro‐octahydroimidazo‐[4,5‐d]imidazole), and ε‐HNIW (ε‐2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane). The detonation velocities, D, were determined. Detonation parameters were also calculated by means of modified Kamlet & Jacobs method, CHEETAH and EXPLO5 codes. In accordance with our expectations BCHMX based PBXs performed better than RDX based ones. The Urizar coefficient for Fuorel binder was also calculated.

Combustion mechanism of RDX and HMX and possibilities of controlling the combustion characteristics of systems based on them

Modeling of the combustion of cyclic nitramines (CNAs) has shown that their combustion proceeds by the same mechanism with the joint effect of the processes in the condensed and gas phases. The combustion characteristics of the pure substances can be changed only at low pressures by using catalysts acting in the condensed phase, and at high pressures, this problem is difficult to solve. The combustion of binary compositions [CNA + fuel (F) and CNA + ammonium perchlorate (AP)] and ternary compositions (AP + CNA + F) is considered. It is shown that the combustion mechanism and characteristics are determined by the chemical interaction and heat exchange between the reactants, which depend on the characteristic particle size in the system.

An improved simple method for prediction of entropy of fusion of energetic compounds

A new general method has been introduced for prediction of entropy of fusion of important classes of energetic compounds including polynitro arene, acyclic and cyclic nitramine, nitrate ester and nitroaliphatic compounds. It extends earlier work, which was restricted to nitroaromatic compounds, to estimate entropy of fusions of any compound containing at least one of the groups ArNO2, CNO2, CONO2 or NNO2 through additive and correcting non-additive functions. The number of nitrogen and oxygen atoms in an energetic compound was used as additive function. For 92 compounds (corresponding to 167 measured values) belong to different types of energetic materials, the root-mean square (rms) deviation of the additive part is 13.5J/(Kmol). The reliability of the new model can be increased by considering one correcting non-additive function for which the value of rms deviation is 10.2J/(Kmol). The predicted outcomes of the new method, by using only additive part or both additive and non-additive functions, give more reliable results as compared to one of the best available methods.

Notes on the use of the vacuum stability test in the study of initiation reactivity of attractive cyclic nitramines in the C4 matrix

Notes on the use of the vacuum stability test in the study of initiation reactivity of attractive cyclic nitramines in the C4 matrix

Explosive Strength and Impact Sensitivity of Several PBXs Based on Attractive Cyclic Nitramines

Plastic explosives based on different cyclic nitramines with different polymeric matrices were prepared and studied. The used polymeric matrices were fabricated on the basis of polyisobutylene (PIB), acrylonitrile-butadiene rubber (ABR), Viton A, and polydimethyl-siloxane as binders, whereas the nitramines named RDX (1,3,5-trinitroperhydro-1,3,5-triazine), β-HMX (β-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), BCHMX (cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole) and ε-HNIW (ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) were used as explosive fillers. Commercial Semtex 10, based on pentaerythritol tetranitrate (PETN), was used for comparison. Impact sensitivity, loading density, ρ, detonation velocity, D, and relative explosive strength (RS) measured by ballistic mortar were determined. It was concluded that plastic BCHMX based on Viton A or PIB-matrix exhibits higher RS compared with PBXs based on RDX and HMX. Correlations between RS and the impact sensitivity, the ρD2 term and the square of the detonation velocity were studied and discussed. The results confirm the well-known fact that increasing the performance is usually accompanied by an increase in the sensitivity of the explosives. In this connection, Viton A enables achieving a high RS, but with a relatively high sensitivity of the PBXs, whereas the polydimethyl-siloxane matrix should perhaps give PBXs with optimum explosive strength and sensitivity parameters.

Thermal behavior and decomposition kinetics of Formex-bonded explosives containing different cyclic nitramines

Thermal behavior and decomposition kinetics of Formex-bonded PBXs based on some attractive cyclic nitramines, such as 1,3,5-trinitro-1,3,5-triazinane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). Actually, cis-1,3,4,6-tetranitrooctahy droimidazo-[4,5-d]imidazole (BCHMX) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10, 12-hexaazaisowurtzitane (CL-20), was investigated by means of nonisothermal thermogravimetry (TG) and differential scanning calorimetry (DSC). It was found that the mass loss rate of PBXs involved in this research depends greatly on heating rate and the residue of the decomposition of these PBXs decreases with the heating rate. The onset of the exotherms was noticed at 215.4, 278.7, 231.2 and 233.7 °C with the peak maximum at 235.1, 279.0, 231.2 and 233.7 °C for RDX-Formex, HMX-Formex, CL-20-Formex, and BCHMX-Formex, respectively. Their corresponding exothermic changes were 1788, 1237, 691, and 1583 J g−1. It was also observed that the dependence on the heating rate for onset temperatures of HMX- and BCHMX-based PBXs was almost the same due to their similar molecular structure. In addition, based on nonisothermal TG data, the kinetic parameters for thermal decomposition of these PBXs were calculated by isoconversional methods. It was shown that the Formex base has great effects on the activation energy distribution of nitramines. It was further found that the kinetic compensation effects occurred during the thermal decomposition of nitramine-based PBXs, and they almost have the same compensation effects due to similar decomposition mechanism.

Note on the use of the vacuum stability test in the study of initiation reactivity of attractive cyclic nitramines in Formex P1 matrix

The zero-order reaction rates (specific rate constants) for isothermal decomposition at 120 °C of plastic bonded explosives (PBXs) were measured by means of the Czech vacuum stability test, STABIL. The PBXs are based on 1,3,5-trinitro-1,3,5-triazinane (RDX), β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d] imidazole (BCHMX), and e-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (e-HNIW, e-CL-20) with 9 wt.% of the C4 type matrix, i.e., a matrix containing 25 wt.% of polyisobutylene, 59 wt.% of dioctyl sebacate and 16 wt.% of the oil HM46. Dependencies were found between the specific rate constants mentioned and the detonation velocities of the PBXs, and consequently between these constants and the impact of pure explosive fillers, i.e., RDX, β-HMX, e-HNIW, RS-e-HNIW, and BCHMX and, at the same time, the corresponding PBXs. The results obtained are compared with those from a recent analogous study of PBXs using an SBR (Formex P1) binder which could increase the PBXs’ reactivity in comparison with C4 matrix. These results also help to dispel a widely held view about HNIW being a relatively sensitive explosive.

Involvement of cytochrome c CymA in the anaerobic metabolism of RDX by Shewanella oneidensis MR-1

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a cyclic nitramine explosive commonly used for military applications that is responsible for severe soil and groundwater contamination. In this study, Shewanella oneidensis MR-1 was shown to efficiently degrade RDX anaerobically (3.5µmol·h(-1)·(g protein)(-1)) via two initial routes: (1) sequential N-NO(2) reductions to the corresponding nitroso (N-NO) derivatives (94% of initial RDX degradation) and (2) denitration followed by ring cleavage. To identify genes involved in the anaerobic metabolism of RDX, a library of ~2500 mutants of MR-1 was constructed by random transposon mutagenesis and screened for mutants with a reduced ability to degrade RDX compared with the wild type. An RDX-defective mutant (C9) was isolated that had the transposon inserted in the c-type cytochrome gene cymA. C9 transformed RDX at ~10% of the wild-type rate, with degradation occurring mostly via early ring cleavage caused by initial denitration leading to the formation of methylenedinitramine, 4-nitro-2,4-diazabutanal, formaldehyde, nitrous oxide, and ammonia. Genetic complementation of mutant C9 restored the wild-type phenotype, providing evidence that electron transport components have a role in the anaerobic reduction of RDX by MR-1.

Theoretical Studies on the Heats of Formation, Detonation Properties, and Pyrolysis Mechanisms of Energetic Cyclic Nitramines

Density functional theory calculations were performed to find comprehensive relationships between the structures and performance of a series of highly energetic cyclic nitramines. The isodesmic reaction method was employed to estimate the heat of formation. The detonation properties were evaluated by using the Kamlet-Jacobs equations based on the theoretical densities and HOFs. Results indicate the N-NO(2) group and aza N atom are effective substituents for enhancing the detonation performance. All cyclic nitramines except C11 and C21 exhibit better detonation performance than HMX. The decomposition mechanism and thermal stability of these cyclic nitramines were analyzed via the bond dissociation energies. For most of these nitramines, the homolysis of N-NO(2) is the initial step in the thermolysis, and the species with the bridged N-N bond are more sensitive than others. Considering the detonation performance and thermal stability, twelve derivatives may be the promising candidates of high energy density materials (HEDMs). The results of this study may provide basic information for the further study of this kind of compounds and molecular design of novel HEDMs.

Simple Pathway to Predict the Power of High Energy Materials

A new method has been introduced to predict the power of important classes of energetic compounds including nitroaromatics, acyclic and cyclic nitramines, nitrate esters and nitroaliphatics. In this method, the predicted specific impulse and the corrected heat of detonation on the basis of H2O-CO2 arbitrary decomposition, have been used to calculate the power of an explosive with the molecular formula CaHbNcOd as determined by the Trauzl test. The predicted results show good agreement with respect to the measured values for both pure and mixture of explosives. The calculated volume expansions of pure energetic compounds have a root mean square (rms) deviation of 33 cm3 from 73 measured values (corresponding to 58 molecules). For 9 explosive mixtures, the predicted volume expansions have an rms deviation of 39 cm3 from the experimental results.

Study of Plastic Explosives based on Attractive Cyclic Nitramines Part I. Detonation Characteristics of Explosives with PIB Binder

AbstractFour plastic explosives based on energetic nitramines and a non‐energetic binder were prepared and studied. The nitramines were RDX (1,3,5‐trinitro‐1,3,5‐triazine), HMX (1,3,5,7‐tetranitro‐1,3,5,7‐tetrazine), BCHMX (cis‐1,3,4,6‐tetranitro‐octahydroimidazo‐[4,5‐d]imidazole) and HNIW (ε‐2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane, ε‐CL‐20). The binder was in all cases polyisobutylene (PIB) as in the standard composition C‐4. These powerful plastic explosives were compared to standard PETN‐based commercially available explosives Semtex 1A and Sprängdeg m/46. The detonation velocities were experimentally measured and compared to the ones calculated by the Kamlet–Jacobs method, CHEETAH and EXPLO5 Codes. The experimental detonation velocities as well as the calculated detonation parameters decrease in the following order: HNIW‐PIB>HMX‐PIB≥BCHMX‐PIB>RDX‐PIB>Sprändeg m/46≥Semtex 1A. Urizar coefficients for the various binders were calculated from experimental data.

Improved reliable approach to predict melting points of energetic compounds

A new general method has been introduced for prediction of melting points of important classes of energetic compounds including polynitro arene, polynitro heteroarene, acyclic and cyclic nitramine, nitrate ester and nitroaliphatic compounds. It extends earlier works, which were used for certain classes of energetic compounds, to estimate melting points of any compound containing at least one of the groups Ar–NO 2, C–NO 2, C–ONO 2 or N–NO 2 through additive and non-additive functions. Elemental composition of an energetic compound of composition C x H y N v O w was used as additive function. The methodology assumes that non-additive function of desired compound can be approximated as the difference between the positive and negative contributions of specific structural moieties. The new model is applied for 149 different energetic compounds including complex molecular structures. For those energetic compounds where one of well-developed group additivity methods can be applied, it is shown that average deviation of the new method is much lower. The new method also gives better predictions as compared to another new and suitable model, which is based on division of the calculated enthalpy of melting to entropy of melting.

Thermal decomposition of cis-2, 4, 6, 8-tetranitro-1H, 5H-2, 4, 6, 8-tetraazabicyclo[3.3.0]octane

The thermal decomposition kinetics of cis-2, 4, 6, 8-tetranitro-1H, 5H-2, 4, 6, 8-tetraazabicyclo[3.3.0]octane was measured in various solvents and in the solid phase by the manometric method. The general regularities for cyclic nitramines concerning the possibility of chain decomposition in hydrocarbon solvents, the kinetic display of cell effect in viscous media, a decrease in the decomposition rate in the solid state, and the quantitative description of this effect in terms of the model of monomolecular reactions in molecular crystals are supplemented and discussed. The dependence of the decomposition rate constants in solutions on the N-N bond lengths in a series of secondary nitramines was shown using the correct values of decomposition rate constants.

Horizontal gene transfer (HGT) as a mechanism of disseminating RDX-degrading activity among Actinomycete bacteria

Hexahydro-1,3,5-trinitro-1,3,5,-triazine (RDX) is a cyclic nitramine explosive that is a major component in many high-explosive formulations and has been found as a contaminant of soil and groundwater. The RDX-degrading gene locus xplAB, located on pGKT2 in Gordonia sp. KTR9, is highly conserved among isolates from disparate geographical locations suggesting a horizontal gene transfer (HGT) event. It was our goal to determine whether Gordonia sp. KTR9 is capable of transferring pGKT2 and the associated RDX degradation ability to other bacteria. We demonstrate the successful conjugal transfer of pGKT2 from Gordonia sp. KTR9 to Gordonia polyisoprenivorans, Rhodococcus jostii RHA1 and Nocardia sp. TW2. Through growth and RDX degradation studies, it was demonstrated that pGKT2 conferred to transconjugants the ability to degrade and utilize RDX as a nitrogen source. The inhibitory effect of exogenous inorganic nitrogen sources on RDX degradation in transconjugant strains was found to be strain specific. Plasmid pGKT2 can be transferred by conjugation, along with the ability to degrade RDX, to related bacteria, providing evidence of at least one mechanism for the dissemination and persistence of xplAB in the environment. These results provide evidence of one mechanism for the environmental dissemination of xplAB and provide a framework for future field relevant bioremediation practices.