Article pubs.acs.org/IECR
Synthesis and Ignition Properties Research of 1,5Diazabicyclo[3.1.0]Hexane Type Compounds as Potential Green Hypergolic Propellants Xing Zhang,† Lianhua Shen,† Yuhong Luo,† Rongpei Jiang,† Haiyun Sun,† Jiuzhou Liu,†,‡ Tao Fang,† Huili Fan,‡ and Zhaoyang Liu*,† †
Beijing Institute of Aerospace Testing Technology, Beijing Key Laboratory of Research and Application for Aerospace Green Propellants, Beijing 100074, China ‡ University of Science and Technology Beijing, Beijing, 100083, China S Supporting Information *
ABSTRACT: 1,5-Diazabicyclo[3.1.0]hexane type compounds (DABHCs) were found as promising liquid hypergolic compounds. The synthesis process and purification of DABHCs, 1,5-diazabicyclo[3.1.0]hexane (DABH), 6-methyl1,5-diazabicyclo[3.1.0]hexane (MDABH), 6-ethyl-1,5diazabicyclo[3.1.0]hexane (EDABH), and 6,6-dimethyl-1,5diazabicyclo[3.1.0]hexane (DDABH) were optimized. The densities of DABHCs were over 1.0 g/mL, and the viscosities of DABHCs were about 2.40−2.63 mPa·s. The boiling points of DABHCs exhibited that they were less volatile, and the freezing points of DABHCs varied considerably for different alkylation. The LD50 predicted values of DABHCs were within 1605.62−4865.43 mg/kg, which demonstrated that DABHCs were grade IV, slightly poisonous, or grade V, nontoxic, compounds according to the Globally Harmonized System of Classification and Labeling of Chemicals (GHS). In addition, the heats of formation of DABHCs were calculated as 129.2−276.2 kJ/mol, higher than those of monomethyl hydrazine, unsymmetrical dimethyl hydrazine, and hydrazine. The ignition delay time of DABH with nitrogen tetroxide was 1 ms, and the ignition delay times of other alkyl substituted DABHCs were 4−11 ms, which indicated the promising application of DABHCs as hypergolic propellants.
1. INTRODUCTION There is an ongoing search for new high energy liquid hypergolic materials used as propellants. As conventional liquid hypergolic propellants, hydrazine and its derivatives in combination with oxidizers such as nitrogen tetroxide (NTO) have been widely applied in rocket propulsion. However, the extremely carcinogenic nature of hydrazine and its derivatives as well as their strong volatility makes it difficult to store and handle such propellants. Therefore, it is urgent to find a way to replace hydrazine and its derivatives in aerospace propulsion applications. There are several well-established tactics for improving the released energy of energetic materials, such as inclusion of nitro and amine groups in molecules and utilizing ringed compounds, which can increase the density of the material, take advantage of ring strain energy during the oxidation reaction, and form more stable reaction products (NO2, CO2, or N2).1 The nitrogen heteroaromatic ring structure has been used to increase the heat of formation. Furthermore, these azo compounds are relatively harmless and eco-friendly in contrast to azobenzene-based compounds, hydrazine and its derivatives.2 © 2017 American Chemical Society
Due to the structure containing N−N and C−N bonds and a tensile ring, 1,5-diazabicyclo[3.1.0]hexane type compounds (DABHCs) usually have high positive formation heat and may be used as potential energetic hypergolic materials. According to Gessner and Ball,1 diaziridine derivatives are important high-energy materials, and it is of great value to investigate the properties of DABHCs. As far as we know, the research on DABHCs was limited to synthesis of 1,5diazabicyclo[3.1.0]hexane (DABH),3−6 and it is usually utilized as an organic7,8 and biological reagent9 at present. However, the detailed synthesis of other 1,5-diazabicyclo[3.1.0]hexane derivatives and their properties for application as liquid hypergolic propellant have not been reported. In this work, the synthesis, reaction time and temperature, and purification conditions of DABHCs including DABH, 6-methyl-1,5diazabicyclo[3.1.0]hexane (MDABH), 6-ethyl-1,5diazabicyclo[3.1.0]hexane (EDABH), and 6,6-dimethyl-1,5Received: Revised: Accepted: Published: 2883
December 14, 2016 February 16, 2017 February 25, 2017 February 26, 2017 DOI: 10.1021/acs.iecr.6b04842 Ind. Eng. Chem. Res. 2017, 56, 2883−2888
Article
Industrial & Engineering Chemistry Research Scheme 1. Synthesis Process of DABHCs
gas chromatograph−mass spectrometer, Agilent Technologies Inc., USA, with an Hp-5 chromatogram column. The density and viscosity values were measured at 25 °C with a SVM3000, Anton Paar, Austria. The freezing point values were obtained with a DSY-021A freezing/cloud/crystallizing point tester, Dalian Petroleum Instrument Co., Ltd., China.
diazabicyclo[3.1.0]hexane (DDABH) were fully explored. The physical properties of DABHCs such as density, viscosity, boiling point, and freezing point were compared with traditional liquid propellants such as monomethyl hydrazine (MMH), unsymmetrical dimethyl hydrazine (UDMH), and hydrazine. In addition, predicted toxicity, heat of formation, and hypergolic ignition characteristics of DABHCs were examined in detail.
3. RESULTS AND DISCUSSIONS 3.1. Synthesis and Optimization of DABHCs. As shown in Scheme 1, the synthesis process of DABHCs consisted of two steps. In the first step, a nucleophilic addition reaction occurred between 1,3-propanediamine and aldehyde (or ketone) following by molecular dehydration, which yielded alkyl substituted hexahydropyrimidine. In the second step, the alkyl substituted hexahydropyrimidine was oxidized by sodium hypochlorite following by the formation of DABHCs. In the synthesis of DABHCs, the time of the first step did not influence the yield obviously when the time of the first step reached 3 h at 25 °C. Aldehyde (or ketone) and 1,3diaminopropane came to reaction immediately when they were mixed together. The first reaction occurred with the reaction heat released prominently ,which was also an apparent evidence of the reaction’s occurrence. Therefore, the reaction time in the first step was fixed to be 3 h at 25 °C. The yields of DABHCs were initially proportional to the second step reaction time, eventually kept constant as shown in Figure 1. When the second step reaction time was 3 h, the yield achieved the highest for DABH, MDABH, and EDABH reached 90%, 82%, and 70%, respectively. However, the
2. EXPERIMENTAL SECTION 2.1. Matetials. 1,3-Propanediamine (98%) was obtained from TCI Co. Ltd. Methyl aldehyde (aqueous, concentration = 37−40%) and acetaldehyde (aqueous, concentration = 40%) were purchased from Tianjin Fuchen Chemical Reagent Co. Ltd. Propyl aldehyde (AR) was bought from Sinopharm Chemical Reagent Co. Ltd. Acetone (AR), methyl alcohol (AR), sodium hypochlorite (AR), and dichloromethane (AR) were obtained from Beijing Chemical Co. Ltd. All reagents in this work were used without further treatment. 2.2. Synthesis Process of DABHCs. Corresponding aldehyde or ketone aqueous solution (1.02 equiv based on effective constituent) was added to 1,3-propanediamine (1.0 equiv) dropwise at a certain temperature with continuous stirring. The reaction continued for enough time. Saturated sodium hypochlorite solution was dropped into the solution with vigorous stirring. After the saturated sodium hypochlorite feeding was finished, the heater was stopped, and the reaction solution was cooled down to the room temperature with the constant stirring. The crude product was obtained. The resultant product was extracted by chloroform. Then residual solvent of the chloroform phase was removed by vacuum evaporation. The initial purities of DABH, MDABH, EDABH, and DDABH were 80%, 78%, 75%, and 69%, respectively. The resultant product was further purified by column chromatography. 2.3. Measurements. The 1H NMR tests were performed with a Bruker DRX400, Germany. The solvent used was CDCl3 with tetramethyl silane (TMS) as a reference reactant. The EI (electron ionization mass spectrometry) tests were performed with a Bruker APEX IV, Germany. The temperature of the ion source was 230 °C. The interface temperature was 280 °C. The electron energy was 70 eV. The scanning range was 35−300 amu. The measurement principles of the 1H NMR and EI tests referred to the literature.10,11 Element analysis results were obtained with a Vario EL elemental analyzer, Elementar Analysensysteme GmbH, Germany. The 1H NMR, EI, and element analysis results of DABHCs are listed in Table S1. The product purities were obtained with an Agilent 7890A/5975C
Figure 1. Yield of DABHCs as a function of second step reaction time (the reaction temperature was 40 °C; each data point was measured based on three parallel synthesis processes). 2884
DOI: 10.1021/acs.iecr.6b04842 Ind. Eng. Chem. Res. 2017, 56, 2883−2888
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purity of DABH reached 99% utilizing column chromatography purification with dichloromethane and methyl alcohol solution (dichloromethane/methyl alcohol = 5:1) as moving phase. Therefore, the moving phase of mixed solution of dichloromethane and methyl alcohol (dichloromethane/methyl alcohol = 5:1 ) was used for purification of DABH, MDABH, EDABH, and DDABH due to the similar structure and reaction properties, and the purities of MDABH, EDABH, and DDABH could all reach up to 99%. The 1H NMR, EI, and element analysis results for DABHCs listed in Table S1 were in accordance with the results reported in the literature5,10 and confirmed the structures of DABHCs. Meanwhile, the similarity of the calculated and found elemental analysis results also proved the high purities of DABHCs. 3.2. The Physical Properties of DABHCs. The physical property values including the densities, viscosities, boiling points, and freezing points of DABHCs are listed in Table 1. The densities of DABHCs were over 1.0 g/mL, reaching 1.03− 1.13 g/mL, and the viscosities of DABHCs were in the range 2.40−2.63 mPa·s. The density and viscosity of DABH were 1.03 g/mL and 2.40 mPa·s, respectively, both lower than those of other alkyl substituted DABHCs. It demonstrated that the introduction of an alkyl group increased the densities and viscosities of DABHCs with the increase of molecular weight. Compared with hydrazine and its derivatives including MMH and UDMH, the densities and viscosities of DABHCs were higher. The densities over 1.0 g/mL suggested the potential excellent unit volume energy performance. The boiling points of DABHCs were relatively higher compared with those of MMH and UDMH, which indicated that DABHCs were less volatile. The freezing points of DABH and MDABH were −9.5 and −4 °C, respectively, higher than those of MMH and UDMH but lower than that of hydrazine, which could be a disadvantage, but it could be improved by complex formulation with other additives with excellent freezing characteristics. The freezing points of EDABH and DDABH were lower than −50 °C, which would be superior for such compounds to be used in space environment with low temperature. Oral rat LD50 value indicates the amount of chemical in mg/ kg body weight that would cause 50% of rats to die after oral ingestion of a test population.14 Among various toxicity prediction tools, the Toxicity Estimation Software Tool (TEST) developed by the U.S. Environmental Protection Agency is a widely used computerized oral acute toxicity predictive system with quantitative structure activity relationships (QSAR) mathematical model methodology.15−18 In order to investigate the toxicity of DABHCs, TEST software was used based on the Food and Drug Administration (FDA) methodology, a typical advanced QSAR mathematical model method-
optimized second step reaction time of DDABH was 5 h, and the yield achieved 70%. In Figure 2, it was observed that the
Figure 2. Yield of DABHCs as a function of second step reaction temperature (the reaction time was 5 h, each data point was measured based on three parallel synthesis processes).
yields of DABH, MDABH, and EDABH grew gradually when the temperature increased from 20 to 40 °C but diminished when the temperature was up to 50 °C. Compared with other DABHCs, the optimized temperature of DDABH was 30 °C; thereby the highest yield was 75%. When the temperature was too high, DABHC hydrochloride might be produced as byproduct, which could not be extracted with chloroform, and led to the decrease of yield. The purities of the resultant DABH, MDABH, EDABH, and DDABH were 80%, 78%, 75%, and 69%, respectively, which were not enough for further utilization as propellants in a rocket engine because the impurities would affect the propulsion performance. Purification was absolutely important to industrial scale production, and different purification methods definitely influenced the purities. Rectification and column chromatography, which were widely applied in chemical industrial production, were chosen as two purification methods for DABH in consideration of the structural similarity of DABHCs. The effects of rectification and column chromatography methods are exhibited in Table S2 and Table S3. The rectification effect improved gradually when the rectification time increased from 6 to 24 h. However, the yield cannot be further improved when the rectification was over 24 h. With the packing’s existence, the purity could not be further improved when the number of theoretical plates increased. In addition, the steaming out of the product became difficult if the temperature was lower than 80 °C. The highest purity of DABH by rectification achieved just 91%. Instead, the
Table 1. Density, Viscosity, Boiling Point, and Freezing Point Values of DABHCs compound DABH MDABH EDABH DDABH MMH12 UDMH13 hydrazine13
densitya (g/mL) 1.03 1.08 1.04 1.13 0.87 0.796 (15 °C) 1.008 (20 °C)
viscositya (mPa·s) 2.40 2.54 2.47 2.63 0.775 0.579 (15 °C) 0.971 (20 °C)
boiling point (°C) 10
58−59 (21 mmHg) 49−5210 (13 mmHg) 127b (760 mmHg) 5710 (7 mmHg) 87 63.1 113.5
freezing point (°C) −9.5 −4 2000 mg/kg), compounds according to the Globally Harmonized System of Classification and Labeling of Chemicals (GHS). Among DABHCs, the LD50 predicted value of DDABH was 4865.43 mg/kg, which was the highest compared with those of other alkyl substituted DABHCs. The toxicity of DABHCs were far lower than that of hydrazine (LD50 = 60 mg/kg) and hydrazine derivatives, such as MMH (LD50 = 32.5 mg/kg) and UDMH (LD50 = 122 mg/kg). 3.3. The Calculation of DABHCs. The thermodynamical properties of diaziridine derivatives are important for the modeling of high-energy materials; the investigation of DABHCs molecule has practical importance besides fundamental research due to the potential application of DABHCs as fuel or rocket propellant. The nature of each stationary point was checked by analytical calculation of harmonic vibrational frequencies. It was revealed that both B3LYP and MP2 methods gave only three minima on a potential hypersurface corresponding to the twist conformation (C2 symmetry) and to the boat and chair (both of Cs symmetry) conformations. Due to the similar structures of DABHCs, DABH was given as an example and its conformation was explored. The most stable conformation of DABH was the boat one as shown in Figure 3, whereas the
compounds
AM1
PM3
MNDO
DABH MDABH EDABH DDABH MMHa UDMHa hydrazinea
276.2 245.6 219.3 225.1
226.1 192.5 174.9 157.7 54.69 53.30 50.45
184.4 162.4 129.2 141.9
a
The formation heat values of MMH, UDMH, and hydrazine were experimental values referred to ref 13, 25.
prominently higher than those of hydrazine (50.45 kJ/mol) and its derivatives including MMH (54.69 kJ/mol) and UDMH (53.30 kJ/mol). Compounds containing nitrogen heterocyclic rings were different from conventional energetic materials. The energy of compounds containing nitrogen rings mostly came from the high heat of formation of N−N and C−N, not the oxidation and burning process of the carbon skeleton.26−28 They had high positive heat of formation values and excellent thermal stability. The highest oxidation state of carbon, when burnt in oxygen, was CO2 and that of hydrogen was H2O. The molecular nitrogen was at a lower state of internal energy than the oxides of nitrogen (NO, NO2, N2O3, etc.). Therefore, any nitrogen in the reactant was given out as N2 gas in the end. The −NO2 and −ONO2 groups were the major source of oxygen in the energetic molecules, which contributed significantly to the combustion processes.29 The main product of burning was nitrogen gas, which did no harm to humans and environment. 3.4. Ignition Delay Research of DABHCs. The ignition is key to liquid hypergolic propellants, which involves the flexibility and controllability of rocket engines and varies with different combinations. The ignition delay time is a crucial factor, which is the time between the instant at which the fuel and oxidizer come in to contact with each other and the time at which combustion occurs with some defined level of energy released. The exact value has a major influence on the optimum dimensions of an engine combustion chamber.25,30 As shown in Figure 4, DABHCs reacted acutely when they came into contact with NTO, and flame appeared immediately. Azo energetic materials typically rely on their efficient gas production and also their high heat of formation for energy release, which produce more gas per gram of energetic materials than other nitrogen-free energetic materials.26 In order to prevent an unwanted collection of fuel and oxidizer, it is important for reactions to progress as rapidly as possible (minimal ignition delay time). In previous studies, 50 ms was the target for the maximum acceptable time for ignition delay.31 Nowadays, the target is within 10 ms or even lower depending on the application. The ignition delay time values of DABH, MDABH, EDABH, and DDABH with NTO as oxidant were measured as 1, 4−5, 10−11, and 4−5 ms, after 3 parallel ignition tests, respectively. The influence of descent velocity of the droplet on the ignition delay time was studied, and it was suggested that the different descent velocities of the droplet did not affect the ignition delay time of DABHCs when the initial height of the droplet was within 6 cm for each DABHC.
Figure 3. Boat conformation of DABH.
MP2 (B3LYP) relative energies for the chair and twist conformations were 15.8(15.3) and 207.41(202.26) kJ mol−1 above the boat form, respectively.20 The molecular point group of DABH in boat conformation was Cs type, and it had a symmetrical plane. It was confirmed by Vishnevskiy20 that the most important stabilization factor in the boat conformation of DABH was the n(N) → σ*(C−C) anomeric effect through the natural bond orbital (NBO) analysis. Heat of formation represents energetic level of fuel or propellant. Semiempirical quantum chemistry AM1, PM3, and MNDO algorithms are common methods in the calculation of the heat of formation. Based on AM1, PM3, and MNDO algorithms described in the literature,21−24 the calculated heat values of formation of DABHCs by AM1, PM3, and MNDO algorithms are listed in Table 3. The calculated heat values of formation of DABHCs were in the range of 129.2−276.2 kJ/mol, and the heat of formation of DABH was the highest among those of DABHCs. The heats of formation of DABHCs were over 100 kJ/mol, which was
4. CONCLUSION DABHCs were found as hypergolic compounds with high heat of formation. The synthesis process of DABHCs consisted of 2886
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Figure 4. Ignition delay test process shown with a series of high speed camera photos at different times when DABHCs came into contact with NTO as oxidizer. Experimental conditions: temperature = 25 °C; environmental pressure = 1.013 × 105 Pa; The purities of DABHCs all reached up to 99%; the initial height of the DABHC droplets from NTO was within 6 cm).
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two steps, nucleophilic addition reaction occurring between 1,3-propanediamine and aldehyde (or ketone) and oxidation reaction of resultant alkyl substituted hexahydropyrimidine with sodium hypochlorite. The time of the first step did not influence the yield obviously when the time of the first step reached 3 h at 25 °C. When the reaction time in the first step was fixed to be 3 h, the optimized reaction time and temperature of the second step for DABH, MDABH, and EDABH were 3 h and 40 °C, respectively, while the optimized reaction time and temperature of the second step for DDABH were 5 h and 30 °C. Rectification and column chromatography methods were compared for the purification of DABH, which demonstrated that column chromatography was a more efficient purification method for DABHCs, and the purities of DABHCs could all reach up to 99% with the moving phase of mixed solution of dichloromethane and methyl alcohol (dichloromethane/methyl alcohol = 5:1) used. The introduction of alkyl group increased the densities of DABHCs, which were all over 1.0 g/mL and suggested the excellent unit volume energy performance. The viscosities of DABHCs were in the range of 2.40−2.63 mPa·s, relatively acceptable in propulsion systems. The density and viscosity results indicated the excellent basic physical properties of DABHCs and laid the foundation for the aerospace propulsion application. DABHCs were less volatile compared with traditional hydrazine compounds (hydrazine, MMH, and UDMH). However, there was a great difference among the freezing points of DABHCs (from −4 °C to less than −50 °C). The predicted LD50 values of DABHCs were over 1600 mg/kg. The calculated heat of formation of DABHCs were in the range of 129.2−276.2 kJ/ mol, which were larger than those of MMH, UDMH, and hydrazine. The ignition delay time values of DABH, MDABH, EDABH, and DDABH with NTO as oxidant were measured as 1, 4−5, 10−11, and 4−5 ms, respectively. As typical azo nitrogen materials, DABHCs, especially DABH, presented distinct advantages (high heat of formation, low toxicity, and extremely short ignition delay time) over conventional energetic materials and may be used as ingredients in liquid hypergolic propellants in consideration of their excellent properties.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.6b04842. 1 H NMR, EI, and element analysis results of 1,5diazabicyclo[3.1.0]hexane type compounds (DABHCs), purities of 1,5-diazabicyclo[3.1.0]hexane (DABH) under different rectification conditions, and purities of DABH under different column chromatography conditions (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail address:
[email protected]. ORCID
Zhaoyang Liu: 0000-0002-5429-6471 Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Gessner, K. J.; Ball, D. W. Cyclic diamines as potential high energy materials. Thermochemical properties of diaziridine, 1,2diazetidine, and 1,3-diazetidine. J. Mol. Struct.: THEOCHEM 2005, 730 (1−3), 95−103. (2) Kim, Y. S.; Son, G. H.; Na, T. K.; Choi, S. H. Synthesis and Physical and Chemical Properties of Hypergolic Chemicals such as N,N,N-Trimethylhydrazinium and 1-Ethyl-4-Methyl-1,2,4-Triazolium Salts. Appl. Sci. 2015, 5 (4), 1547−1559. (3) Bronstert, K. Preparation of diaziridines. Patent DE3607993A1, 1987. (4) Lyalin, B. V.; Petrosyan, V. A. Direct Electrochemical Synthesis of Diaziridines. Russ. J. Electrochem. 2002, 38 (11), 1220−1227. (5) Malone, H. P. Synthesis and conformational analysis of 1,5diazabicyclo[3.1.0]hexanes. Doctoral dissertation, 1971, CAPLUS AN 1972:71880. (6) Terpigorev, A. N.; Kuz’mina, T. V. Kinetics of the synthesis of 1,5-diazabicyclo[3.1.0]hexane. Zh. Prikl. Khim. (S.-Peterburg) 1999, 72 (12), 1990−1999. (7) Bronstert, K. Preparation and use of polymers bearing acid endgroups. Patent DE3709807A1, 1988. 2887
DOI: 10.1021/acs.iecr.6b04842 Ind. Eng. Chem. Res. 2017, 56, 2883−2888
Article
Industrial & Engineering Chemistry Research (8) Denisenko, S. N.; Kaupp, G.; Bittner, A. J.; Rademacher, P. Orbital interactions in diaziridines. J. Mol. Struct. 1990, 240, 305−12. (9) Popov, V. B.; Protasova, G. A.; Shabasheva, L. V.; Men’shikov, N. M.; Radilov, A. S. Dynamics of embryotoxic factors in rat blood following the exposure to 1,5-diazabicyclo(3.1.0)hexane. Toksikol. Vestn. 2002, No. 6, 32−37. (10) Shustov, G. V.; Denisenko, S. N.; Chervin, I. I.; Asfandiarov, N. L.; Kostyanovsky, R. G. Asymmetric Nitrogen 0.41. Stereochemistry of Bicyclic 1,2-Cis-Diaziridines. Tetrahedron 1985, 41 (23), 5719−5731. (11) Rademacher, P.; Koopmann, H. Photoelektronenspektroskopische Konformationsanalyse aliphatischer Hydrazine, 2. Cyclische und bicyclische Hydrazine. Chem. Ber. 1975, 108 (5), 1557−1569. (12) Lee, L. D. Dimethyl-2-azidoethylene, Chemical and Physical Property Data; NASA: Washington, DC, 2000. (13) Yayu, L. Liquid Propellants; China Aerospace Press: Beijing, 2011. (14) Walum, E. Acute oral toxicity. Environ. health persp. 1998, 106, 497. (15) Bakhtyari, N. G.; Raitano, G.; Benfenati, E.; Martin, T.; Young, D. Comparison of In Silico Models for Prediction of Mutagenicity. J. Environ. Sci. Heal. C 2013, 31 (1), 45−66. (16) Chayata, H.; Lassalle, Y.; Nicol, E.; Manolikakes, S.; Souissi, Y.; Bourcier, S.; Gosmini, C.; Bouchonnet, S. Characterization of the ultraviolet-visible photoproducts of thiophanate-methyl using high performance liquid chromatography coupled with high resolution tandem mass spectrometry-Detection in grapes and tomatoes. J. Chromatogr. A 2016, 1441, 75−82. (17) Li, X.; Chen, L.; Cheng, F. X.; Wu, Z. R.; Bian, H. P.; Xu, C. Y.; Li, W. H.; Liu, G. X.; Shen, X.; Tang, Y. In Silico Prediction of Chemical Acute Oral Toxicity Using MultiClassification Methods. J. Chem. Inf. Model. 2014, 54 (4), 1061−1069. (18) White, J.; Wrzesinski, C.; Green, M.; Johnson, G. T.; McCluskey, J. D.; Abritis, A.; Harbison, R. D. A novel method for deriving thresholds of toxicological concern for vaccine constituents. Toxicol. Mech. Methods 2016, 26 (4), 270−275. (19) Contrera, J. F.; Matthews, E. J.; Benz, R. D. Predicting the carcinogenic potential of pharmaceuticals in rodents using molecular structural similarity and E-state indices. Regul. Toxicol. Pharmacol. 2003, 38 (3), 243−259. (20) Vishnevskiy, Y. V.; Vogt, N.; Vogt, J.; Rykov, A. N.; Kuznetsov, V. V.; Makhova, N. N.; Vilkov, L. V. Molecular structure of 1,5diazabicyclo[3.1.0]hexane as determined by gas electron diffraction and quantum-chemical calculations. J. Phys. Chem. A 2008, 112 (23), 5243−5250. (21) Ju, X.-H.; Li, Y.-M.; Xiao, H.-M. Theoretical Studies on the Heats of Formation and the Interactions among the Difluoroamino Groups in Polydifluoroaminocubanes. J. Phys. Chem. A 2005, 109 (5), 934−938. (22) Stewart, J. J. Optimization of parameters for semiempirical methods I. Method. J. Comput. Chem. 1989, 10 (2), 209−220. (23) Stewart, J. J. Semiempirical molecular orbital methods. Reviews in computational chemistry 1990, 1, 45−81. (24) Stewart, J. J. Optimization of parameters for semiempirical methods IV: extension of MNDO, AM1, and PM3 to more main group elements. J. Mol. Model. 2004, 10 (2), 155−164. (25) Mellor, B. A preliminary technical review of DMAZ: a low-toxicity hypergolic fuel; ESA Special Publication: Paris, 2004; p 22. (26) Hiskey, M. A.; Goldman, N.; Stine, J. R. High-nitrogen energetic materials derived from azotetrazolate. J. Energ. Mater. 1998, 16 (2−3), 119−127. (27) Klapötke, T. M. Chemistry of high-energy materials; Walter de Gruyter GmbH & Co KG: Berlin, 2015. (28) Talawar, M. B.; Sivabalan, R.; Mukundan, T.; Muthurajan, H.; Sikder, A. K.; Gandhe, B. R.; Rao, A. S. Environmentally compatible next generation green energetic materials (GEMs). J. Hazard. Mater. 2009, 161 (2−3), 589−607. (29) Badgujar, D. M.; Talawar, M. B.; Asthana, S. N.; Mahulikar, P. P. Advances in science and technology of modern energetic materials: An overview. J. Hazard. Mater. 2008, 151 (2−3), 289−305.
(30) Mellor, B.; Ford, M. Investigation of ignition delay with DMAZ fuel and MON oxidiser, Presented at the 42nd AIAA/ASME/SAE/ ASEE Joint Propulsion Conference & Exhibit, Sacramento, California, 2006. (31) Zhang, Y. Q.; Gao, H. X.; Joo, Y. H.; Shreeve, J. M. Ionic Liquids as Hypergolic Fuels. Angew. Chem., Int. Ed. 2011, 50 (41), 9554−9562.
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