Mass spectrometric studies of the thermal decomposition of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX)

The sublimation and thermal decomposition of HMX were studied by means of Langmuir evaporation and effusion mass spectrometry in the temperature range 175–275°C. Langmuir experiments showed that the primary mechanism for thermal decomposition is ring cleavage to two equal 148 amu species. Decomposition within the effusion cell produced numerous smaller molecules and free radicals due to the decomposition of the 148 amu molecule.     

Synthesis of 1,3,5,7-tetraazacyclooctane derivatives

Tetraazaadamantane was converted under mild conditions into 1,3,5,7-tetraazabicyclo[3.3.1]nonane derivatives. The latter were transformed selectively into 1,3,5,7-tetraazacyclooctane derivatives avoiding the formation of 1,3,5-triazacyclohexane compounds.     

DFT studies of pressure effects on structural and vibrational properties of crystalline octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine

The present study employs density-functional electronic structure methods to investigate the effect of chemical modification at the C5 position of cytosine. A series of experimentally motivated chemical modifications are considered, including alkyl, halogen, aromatic, fused ring, and strong σ and π withdrawing functional groups. The effect of these modifications on cytosine geometry, electronic structure, proton affinities, gas phase basicities, cytosine–guanine base pair hydrogen bond network and corresponding nucleophilicity at guanine are examined. Ultimately, these results play a part in dissecting the effect of endogenous cytosine methylation on the reactivity of neighboring guanine toward carcinogens and DNA alkylating agents.     

First-principles study of the four polymorphs of crystalline octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine

The electronic structure and vibrational properties of the four polymorphs of crystalline octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) have been studied using density functional theory within the local density approximation. The results show that the states of N in the ring make more important contributions to the valence bands than these of C and N of NO2 and so N in the ring acts as an active center. From the low frequency to high-frequency region, the molecular motions of the vibrational frequencies for the four HMX polymorphs present unique features. It is also noted that there is a relationship between the band gap and impact sensitivity for the four HMX polymorphs. From the cell bond order per unit volume, we may infer the variation order of crystal bonding for the four polymorphs and so predict their impact sensitivity order as follows: beta-HMX < gamma-HMX < alpha-HMX < delta-HMX, which is in agreement with their experimental order.     

Potentiometric microdetermination of 1,3,5-trinitro-1,3,5-triazacyclohexane and 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane in several solvents

Pyridine, tetramethylguanidine, and hexamethylphosphoramide were evaluated as solvents for the microdetermination of two weakly acidic compounds of ordnance interest, 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX). The titrant was tetrabutylammonium hydroxide in methanol/ toluene. Endpoints were determined potentiometrically by a glass/modified calomel electrode system or by two polarized platinum electrodes.The largest potentiometric break was found in the very basic solvent tetramethylguanidine. Endpoint detection using two polarized platinum electrodes significantly enhanced the precision of the analysis.     

Initial chemical events in shocked octahydro-1,3,5,7-tetranitro-1,3,5,7- tetrazocine: a new initiation decomposition mechanism

We have performed ab initio molecular dynamics simulations in conjunction with the multiscale shock technique to study the initial chemical processes of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) under shock wave loading. The results show that the initial decomposition of shocked HMX is triggered by the N-O bond breaking and the ring opening. This will initiate many decomposition reactions and lead to the production of many small radicals at a moment. As the shock compression continues, these small radicals recombine to produce many large radicals and further form ring-shaped radicals. Then, these radicals begin to further decompose. It is also found that the system transiently produces a large number of metallic states under the shock compression. Our simulations thus suggest a new mechanism for the initial chemical processes of shocked HMX and provide fundamental insight into the initial mechanism at the atomistic level, which is of important implication for understanding and development of energetic materials.     

Liquid chromatography/electrospray ionization tandem mass spectrometry analysis of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)

A quantitative liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method was developed for the analysis of the explosive, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). In negative ionization mode, HMX forms an acetate adduct ion [M + CH(3)COO](-), m/z 355, in the presence of a small amount of acetic acid in the mobile phase. The ESI collision-induced dissociation (CID) spectrum of m/z 355 was acquired and the transitions m/z 355 --> 147 and m/z 355 --> 174 were chosen for the determination of HMX in samples. Using this quantification technique, the method detection limit was 1.57 microg/L and good linearity was achieved in the range 5-500 microg/L. This method will help to unambiguously analyze environmentally relevant concentrations of HMX.     

Method optimization for quantitative analysis of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) by liquid chromatography-electrospray ionization mass spectrometry

A simple, sensitive LC-ESI-MS method was optimized for quantitative analysis of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in environmental samples. Under negative ionization mode, HMX can form adduct ions with various organic acids and salts, including acetic acid, formic acid, propionic acid, ammonium nitrate, ammonium chloride, sodium nitrite, and sodium nitrate. Acetic acid was chosen as additive and the ion, [M + CH₃COO]⁻ with m/z = 355 was used for selective ion monitoring (SIM) in this study. Good sensitivity was achieved with low acetic acid concentration in the mobile phase and relatively low capillary temperature. The method detection limit was 0.78 pg for HMX in standard solution. Linearity (R² > 0.9998) was obtained at low concentrations (0.5-50 μg/L). This method has been used to determine HMX concentrations in water samples and lizard egg samples from an animal exposure study.     

Development of an extraction and cleanup procedure for a liquid chromatographic-mass spectrometric method to analyze octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine in eggs

An efficient sample extraction and cleanup method was developed for determination of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in eggs. The procedure included solvent extraction of HMX from eggs followed by cleanup using florisil and styrene-divinylbenzene (SDB) cartridges. Homogenized egg aliquots were thoroughly mixed with 10 mL acetonitrile and extracted with ultrasonication for 1 h. Each sample was centrifuged and all liquid was collected for cleanup. After concentration by N₂ evaporation, each extract was cleaned by florisil and SDB cartridges to remove endogenous interfering compounds. Finally, each extract was filtered through a 0.2 μm PTFE membrane and stored for liquid chromatographic-mass spectrometric (LC-MS) analysis. Chromatographic separation was achieved on a reverse phase (RP) C18 column, with a mobile phase containing 60% methanol + 40% 1.0 mM acetic acid aqueous solution. Acetic acid was employed as mobile phase additive to form negatively charged adduct ions [M + CH₃COO]⁻, and m/z = 355 was quantified by selective ion monitoring (SIM). Overall recoveries from eggs containing 10, 50, 250 and 1000 ng/g of HMX were 84.0%, 88.0%, 90.6% and 87.4%. A method detection limit (MDL) of 0.15 ng/g was achieved.     

奥克托金(HMX)的T-Jump/FTIR快速热裂解研究

采用T-Jump/FTIR快速热裂解原位红外光谱联用技术研究了奥克托金(HMX)在0.1,0.2,0.3和0.4MPa的Ar气条件下,以1000℃·s-1的升温速率快速升温至设定的反应温度,用快速扫描傅立叶变换红外光谱跟踪分析分解产物的种类和相对摩尔浓度的变化,研究了温度及压力对初始检测产物的影响.结果表明,HMX在快速热裂解5s过程中红外所检测到的主要气相产物为CO,CO2,NO,NO2,N2O,HCONH2,CH2O,H2O,HNCO及HCN,并给出了这些产物相对摩尔浓度随时间变化的曲线.根据气体产物相对摩尔浓度的比率N2O/HCN,研究了压力和反应温度对HMX的快速热裂解过程及机理的影响,认为在低温HMX分解的C—N键断裂在两竞争反应中占优,通过压力的变化证明了气相产物之间存在二次反应.     

Determination of heats of decomposition of some 1,3,5,7-tetraazacyclooctane and 1,3,5-triazacyclohexane derivatives using differential scanning calorimetry

Differential scanning calorimetry was used to determine the heats of decomposition of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane(HMX), 1,5-diacetyl-3,7-dinitro-1,3, 5,7-tetraazacyclooctane(DADN), 1,5-endomethylene-3,7-dinitro-1,3,5,7-tetraazacyclooctane(DPT), 1,3,5-trinitro-1,3,5-triazacyclohexane(RDX), 1,3,5-trinitroso-1,3,5-triazacyclohexane (R-salt), and 1,5-endomethylene-3,7-dinitroso-1,3,5,7-tetraazacyclooctane(DNPT). The value of the decomposition heat of unit mass of sample was found to increase inHMX, DADN andRDX with decreasing degree of filling of the reaction volume. In the R-salt and inDNPT, however, the trend of this dependence was found to be the reverse and more pronounced. No analogous dependence was found to exist forDPT under the given experimental conditions.

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Zusammenfassung Die Bestimmung der Zersetzungswärmen von 1,3,5,7-Tetranitro-1,3,5,7-tetraazacyclooktan(HMX), 1,5-Diacetyl-3,7-dinitro-1,3,5,7-tetraazacyclooktan(DADN), 1,5-Endomethylen-3,7-dinitro-1,3,5,7-tetraazacyclooktan (DPT), 1,3,5-Trinitro-1,3,5-triazacyclohexan(RDX), 1,3,5-Trinitroso-1,3,5-triazacyclohexan (R-salz) und 1,5-Endomethylen-3,7-dinitroso-1,3,5,7-tetraazacyclooktan(DNPT) wurde mittels Differential-Abtastkalorimetrie durchgeführt. Es wurde festgestellt, daß der Wert der Zersetzungswärme der Masseneinheit der Probe beiHMX, DADN undRDX mit abnehmendem Füllungsgrad des Reaktionsvolumens zunimmt. Bei R-salz undDNPT war hingegen die Richtung der Abhängigkeit umgekehrt und stärker. Keine analoge Abhängigkeit wurde fürDPT unter den Bedingungen des obigen Versuchs gefunden.

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Résumé On a déterminé par analyse calorimétrique différentielle les chaleurs de décomposition des composés suivants: 1,3,5,7-tétranitro-1,3,5,7-tétraazacyclooctane (HMX), 1,5-diacé tyle-3,7-dinitro-1,3,5,7-tétraazacyclooctane(DADN), 1,5-endométhylène-3,7-dinitro-1,3,5,7-tétraazacyclooctane(DPT), 1,3,5-trinitro-1,3,5-triazacyclohexane(RDX), 1,3,5-trinitroso-1,3,5-triazacyclohexane (selR) et 1,5-endométhylène-3,7-dinitroso-1,3,5,7-tétraazacyclooctane(DNPT). La valeur de la chaleur de décomposition par masse unité d'échantillon augmente dans le cas deHMX, DADN etRDX, quand le degré de remplissement du volume réactionnel diminue. On a trouvé, cependant, avec le selR et leDNPT, une dépendance inverse et plus prononcée. Aucune dépendance similaire n'a été trouvée, dans les conditions expérimentales appliquées dans le cas duDPT.

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The authors express their gratitude to Mr. Milan Andoga for his precise DSC measurements.     

Identification of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) pyrolysis products by simultaneous thermogravimetric modulated beam mass spectrometry and time-of-flight velocity-spectra measurements

The pyrolysis products formed during the isothermal decomposition of HMX at 211°C are H₂O, HCN, CO, CH₂O, NO, N₂O, methylformamide, C₂H₆N₂O, octahydro-1-nitroso-3,5,7-trinitro-1,3,5,7-tetrazocine, and a nonvolatile residue. The temporal behaviors of these products during the decomposition are presented. The method for using time-of-flight (TOF) velocity spectra to assist mass-spectrometry measurements in identifying the different gaseous products formed from the pyrolysis of a material by determining the approximate molecular weights of the different gaseous products contributing to the different m/z values in the mass spectrum of the mixture is described. The ion fragmentation of HMX as a function of electron energy shows complete fragmentation of the HMX molecular ion for electron energies ≥ 12.4 eV. No fragments from the pyrolysis of HMX other than those mentioned above are observed.     

The surface and solution properties of dihexadecyl dimethylammonium bromide

The surface adsorption behavior and solution aggregate microstructure of the dichain cationic surfactant dihexadecyl dimethylammonium bromide (DHDAB) have been studied using small angle neutron scattering (SANS), light scattering, neutron reflectivity (NR), and surface tension (ST). Using a combination of surface tension and neutron reflectivity, the DHDAB equilibrium surface excess at saturation adsorption has been measured as 2.60 +/- 0.05 x 10 (-10) mol.cm (-2). The values obtained by both methods are in good agreement and are consistent with the values reported for other dialkyl chain surfactants. The critical aggregation concentration (CAC) values obtained from both methods (NR and ST) are also in good agreement, with a mean value for the CAC of 4 +/- 2 x 10 (-5) M. The surface equilibrium is relatively slow, and this is attributed to monomer depletion in the near surface region, as a consequence of the long monomer residence times in the surfactant aggregates. The solution aggregate morphology has been determined using a combination of SANS, dynamic light scattering (DLS), cryogenic transmission electron microscopy (CryoTEM), and ultrasmall angle neutron scattering (USANS). Within the concentration range 1.5-80 mM, the aggregates are in the form of bilamellar vesicles with a lamellar " d-spacing" of the order of 900 A. The vesicles are relatively polydisperse with a particle size in the range 2000-4000 A. Above 80 mM, the bilamellar vesicles coexist with an additional L beta lamellar phase.     

Kinetics of the β → δ solid-solid phase transition of HMX, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine

We apply differential scanning calorimetry (DSC) to measure the kinetics of the β→δ solid-solid phase transition of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, HMX. Integration of the DSC signal gives a direct measurement of degree of conversion. Data is analyzed by first-order kinetics, the Ozawa method, and isoconversional analysis. The range of activation energies found in this work, centering around 500 kJ/mol, is much higher than previously reported values by Brill and co-workers [AIAA J. (1982)], 204 kJ/mol [1], and Henson et al. and Henson and co-workers [B. Henson, L. Smilowitz, B. Asay, P. Dickson, Thermodynamics of the beta to delta phase transition in PBX-9501, in: Proceedings of American Physical Society Topical Group on Shock Compression of Condensed Matter, American Institute of Physics, Atlanta, GA, 2001; L. Smilowitz, B. Henson, J. Robinson, P. Dickson, B. Asay, Kinetics of the beta to delta phase transition in PBX-9501, in: Proceedings of American Physical Society Topical Group on Shock Compression of Condensed Matter, American Institute of Physics, Atlanta, GA, 2001; P.M. Dickson, B.W. Asay, B.F. Henson, C.S. Fugard, J. Wong, Measurement of phase change and thermal decomposition kinetics during cookoff of PBX-9501, in: Proceedings of American Physical Society Topical Group on Shock Compression of Condensed Matter, American Institute of Physics, Snowbird, UT, 1999], 200 kJ/mol [4]. We discuss possible reasons for the higher activation energies measured here but do not identify the cause.     

Detection of the cyclic nitramine explosives hexahydro-1,3,5-trinitro- 1,3,5-triazine (RDX) and octahydro- 1,3,5,7-tetranitro- 1,3,5,7-tetrazine (HMX) and their degradation products in soil environments

The cyclic nitramine explosives hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX) were examined in field and microcosm soil samples to determine their patterns of degradation and environmental fates. A number of analytical techniques, including solid-phase microextraction with on-fiber derivatization, gas chromatography-mass spectrometry, gas chromatography with electron-capture detection, liquid chromatography-mass spectrometry, and micellar electrokinetic chromatography were required for the analyses. Two different classes of intermediates were detected, both of which lead ultimately to the formation of nitrous oxide (N2O) and carbon dioxide (CO2). The first class was identified as the nitroso derivatives formed by the sequential reduction of -NO2 functional groups. The second class of intermediates, which was favored at higher humidities and in the presence of anaerobic sludge amendments, consisted of ring cleavage products including bis-(hydroxymethyl)-nitramine and methylenedinitramine. Rye-grass (Lolium perenne) present in field samples was found to extract and accumulate HMX from soil without further degradation. In all cases (excepting the plant samples), the indigenous microbes or amended domestic anaerobic sludge consortia degraded the cyclic nitramine explosives eventually to produce N2O and CO2.