Letter Cite This: Org. Lett. XXXX, XXX, XXX−XXX
pubs.acs.org/OrgLett
Construction of Polynitro Compounds as High-Performance Oxidizers via a Two-Step Nitration of Various Functional Groups Gang Zhao,† Dheeraj Kumar,† Ping Yin,† Chunlin He,† Gregory H. Imler,‡ Damon A. Parrish,‡ and Jean’ne M. Shreeve*,† †
Department of Chemistry, University of Idaho, Moscow, Idaho 83844-2343, United States, Naval Research Laboratory, 4555 Overlook Avenue, Washington, DC 20375, United States
‡
Org. Lett. Downloaded from pubs.acs.org by EASTERN KENTUCKY UNIV on 01/24/19. For personal use only.
S Supporting Information *
ABSTRACT: An oxygen-rich energetic compound, 1,3-bis(trinitromethyl)-1,2,4-triazole (13), was obtained by a two-step nitration and found to have an excellent crystal density of 1.90 g/cm3 confirmed by X-ray single-crystal diffraction. This highly dense material, as a green energetic oxidizer, features an attractive positive oxygen balance, an acceptable sensitivity, and a good enthalpy of formation, making it a competitive replacement for AP.
A
mmonium perchlorate (AP) dominates the solid rocket propellant field because perchlorate is a powerful oxidizer and the ammonium cation serves as a good fuel.1 This combination has many advantages; for example, it is inexpensive and has a high specific impulse.2 However, its instability, high negative enthalpy of formation, and claimed health and environmental issues caused by its combustion products limit its utilization.3,4 Therefore, significant progress toward developing environmentally friendly oxidizers has been made to replace AP in the area of energetic materials.5 Ammonium dinitramide (ADN) and hydrazinium nitroformate (HNF) are often suggested as chlorine-free substitutes; however, they also have several drawbacks such as having much higher sensitivities, lower thermal stabilities, hygroscopic characteristics, and negative heats of formation.6 Polynitro compounds with trinitromethyl or dinitromethyl moieties are among the most promising substituents to be used in high energy density oxidizers.7 In recent years, five- or sixmembered heterocyclic compounds have emerged as very promising scaffolds for the design and syntheses of high energy density oxidizers.8 Heterocyclic compounds containing trinitromethyl groups are usually synthesized by introduction of the trinitroethyl building block (Figure 1A) or direct nitration. So far, several methods to introduce the trinitromethyl group into heterocyclic compounds by nitration have been demonstrated. Recently, a general approach to synthesize polynitro materials by mixed acid nitration of heterocyclic compounds containing an acetonyl or an ethyl acetate group was reported (Figure 1B,C).7 Considering the mechanism of the nitration reaction, the acetonyl or the ethyl acetate group is oxidized by the nitronium ion, while N2O5 is the effective nitrating reagent © XXXX American Chemical Society
Figure 1. (A) Trinitroethyl building block. (B) Nitration of the acetonyl group by mixed acid. (C) Nitration of the ethyl acetate group by a two-step nitration. (D) This work. (E) This work.
(N2O5 or TFAA/HNO3) in the nitration of chloroxime derivatives.9 Special attention would be required in order to design a synthetic route and to select the proper nitrating reagent if both acetonyl and chloroxime groups were present in a molecule. There are no literature examples of the nitration of such heterocyclic compounds. We now report progress in sequential nitration of heterocyclic compounds. The trinitromethyl group can be Received: December 26, 2018
A
DOI: 10.1021/acs.orglett.8b04114 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters
tromethyl intermediate was formed, which could be dissolved subsequently in methanol and treated with KI to give the potassium salt (11). Neutral compound 12 was obtained by treating 11 with concentrated sulfuric acid at 0 °C. Then the two trinitromethyl groups in 13 were formed in the presence of sulfuric and nitric acids at 0 °C. Suitable crystals were obtained for 6, 7, and 13 by slow evaporation of their saturated solutions in methanol, and their crystal structures are given in Figures 2−4. Compounds 7 and
obtained from a cyano group by a two-step nitration. The acetonyl group was found to tolerate TFAA/HNO3, while the chloroxime group decomposes in mixed acid. Compounds 7 and 13 were synthesized using a two-step nitration. Both of them are new highly dense oxidizers with high performance necessary for rocket propellants. Compound 2 was synthesized in high yield starting from commercially available 3-cyano1,2,4-triazole (1).5g,h,10 The amidoxime derivative 3 was obtained when 2 was reacted with aqueous hydroxylamine (Scheme 1). Diazotization in hydrochloric acid led to the Scheme 1. Synthesis of 6 (1,1′-Methylenebis(1H-1,2,4triazole-3,1-diyl))bis(dinitromethanide)) and 7 ((Bis(3(trinitromethyl)-1H-1,2,4-triazol-1-yl)methane))
Figure 2. (a) Thermal ellipsoid plot (50%) and labeling scheme for 6. (b) Ball-and-stick packing diagram of 6 viewed down the a axis.
formation of the chloroxime 4. Compound 5 formed when 4 was stirred with TFAA/HNO3, followed by workup with potassium iodide in methanol. The neutral compound 6 was obtained upon acidification of 5 with concentrated sulfuric acid at 0 °C. Further nitration of 6 with a mixture of sulfuric acid and nitric acid proceeds smoothly to give 7 as a white solid in 80% yield. This is the first example of a transformation from a cyano group to a trinitro group by a two-step nitration; TFAA/ HNO3 was used in the first step, and H2SO4 and HNO3 were used in the second step. Interestingly, when 3-cyano-1,2,4triazole was treated with sodium hydroxide and chloroacetone was added, 8 was obtained in high yield (Scheme 2). The
Figure 3. (a) Thermal ellipsoid plot (50%) and labeling scheme for 7. (b) Ball-and-stick packing diagram of 7 viewed down the a axis.
Scheme 2. Synthesis of 13 (1,3-Bis(trinitromethyl)-1H1,2,4-triazole) Figure 4. (a) Thermal ellipsoid plot (50%) and labeling scheme for 13. (b) Ball-and-stick packing diagram of 13 viewed down the a axis.
13 crystallize in the orthorhombic space groups Pccn and Pca21, respectively, whereas 6 crystallizes in the monoclinic space group P21/c.The crystal of 13 has two molecules in the asymmetric unit, with bond lengths and bond angles differing slightly. Compound 13 exhibits an excellent crystal density of 1.90 g/cm3 (T = 293 K). In 13, the trinitromethane moieties are nearly perpendicular to the triazole rings with the dihedral angle between the mean plane through three nitrogen atoms of C(NO2)3 moieties and mean plane through the triazole rings lying in the range of 82.7(5) to 87.1(6)°. To gain more insight into the relationship between structure and physical properties, the Hirshfeld surfaces and twodimensional fingerprint spectra of 6, 7, and 13 were analyzed by using Crystalexplorer17.5.
reaction of hydroxylamine with the nitrile 8 led to the formation of the corresponding amidoxime derivative 9. The chloroxime compound 10 was obtained by stirring 9 with sodium nitrite in hydrochloric acid at 0−5 °C. The chloroxime group is not stable in H2SO4/HNO3, but the acetonyl group is. When 10 was treated with TFAA/HNO3, the chlorodiniB
DOI: 10.1021/acs.orglett.8b04114 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters
Figure 5. Hirshfeld surface calculations of 6, 7, and 13 as well as two-dimensional fingerprint plots in the crystal structures. Images (a), (e), and (i) are the Hirshfeld surfaces that use color coding to represent the proximity of close contacts around 6, 7, and 13 molecules (white, d = van der Waals (vdW) distance; blue, d > vdW distance; red, d < vdW distance). The fingerprint plots in crystal stacking found in 6 (b), 7, (f) and 13 (j). Images (c), (j), and (k) show the O···O atomic contact percentage contribution to the Hirshfeld surface for 6, 7, and 13. The pie graphs (d), (h), and (l) for 6, 7, and 13 show the percentage contributions of the individual atomic contacts to the Hirshfeld surface.
Table 1. Physical and Energetic Properties of 6, 7, and 13 ρc(g cm−3) Dve (m/s) Pf (GPa) ΔHfg (kJ/mol/kJ/g) Tdech (°C) ISi (J) FSj (N) Ispk (s) Ispl (12% Al) (s) OBm (%) On (%) N+Oo (%)
6
7
13
APa
ADNb
RDXb
1.70 7981 26.0 231.4/0.64 99 7 120 231.9 249 −40.2 36 75
1.77 8568 31.4 281.2/0.62 147 6 240 263 268 −14.3 43 80
1.89/1.90d 8434 30.7 22.9/0.06 157 4 120 238 252 15.3 52 87
1.95 6368 15.8 −295.8/ −2.52 >200 15 >360 157 230.5 27.2 54 65
1.81 7860 23.6 −149.8/ −1.13 159 3−5 64−72 202 253.7 25.8 45 97
1.80 8795 34.9 92.6/0.42 204 7 120 258 −21.6 43 81
Reference 7. bReference 8. cDensity measured in a gas pycnometer at 25 °C. dDensity determined by X-ray analysis (at 293 K). eCalculated detonation velocity. fCalculated detonation pressure. gHeat of formation. hTemperature of decomposition (onset). iImpact sensitivity. jFriction sensitivity. kSpecific impulse − isobaric combustion conditions at a chamber pressure of 7 MPa bar versus ambient pressure with equilibrium expansion conditions at the nozzle throat. lSpecific impulse for 88% oxidizer and 12% Al. mOxygen balance based on CO2. For a compound with the molecular formula of CaHbNcOd, ΩCO2 (%) = 1600 [(d − 2a − b/2)/MW]; MW, molecular weight. nOxygen content. oCombined nitrogen and oxygen content. a
many orientations indicating strong intermolecular hydrogen bond interactions. However, for 13, no red dots are seen because of limited hydrogen-bond interactions. In Figure 5b,f, a pair of remarkable spikes at the bottom left indicates O···H, H···O, N···H, and H···N interactions in the 2D fingerprint plots of crystals of 6 and 7 denoting the hydrogen bonds among neighboring molecules,11c while in Figure 5j, essentially no N···H and H···N interactions (0.6%) can be seen, and O··· H, H···O interactions (18.6%) suggest intermolecular hydrogen bonds where the H atom of the triazole moiety interacts
For each point on the Hirshfeld surface, the normalized contact distance (dnorm) was determined by equation [dnorm = (di − divdW)/rivdW + (de − devdW)/revdW] in which di is measured from the surface to the nearest atom interior to the surface interior, while de is measured from the surface to the nearest atom exterior to the surface interior, where rivdW and revdW are the van der Waals radii of the atoms.11 From the images, the red represents the high contact populations, while blue spots are for low contact populations.11 As shown in Figure 5a,e,i, 6 and 7 appear as V-shaped blocks with red dots dispersed in C
DOI: 10.1021/acs.orglett.8b04114 Org. Lett. XXXX, XXX, XXX−XXX
Organic Letters
■
with the O atoms of the nitro group. The percentage of O···O interactions for 6, 7, and 13 are 19.2, 37.7, and 70.7%, respectively, which indicates that 13 will be more dense and compounds as more sensitive than 6 and 7.12 Because the oxygen atoms are in the trinitromethyl groups, higher relative frequencies of close O···O contacts demonstrate more nitro groups exposed on the molecular surface, resulting in an unexpected explosion.12 Heats of formation were calculated using the Gaussian 03 (Revision E.01) suite of programs (Table 1). Compounds 6, 7, and 13 have relatively high positive heats of formation (ΔHf) falling between 0.06 and 0.64 kJ/g, which exceed both AP (−2.52 kJ/g) and ADN (−1.13 kJ/g). The detonation pressures (P) range between 26.0 and 31.4 GPa and the detonation velocities (Dv) between 7981 and 8568 m/s. All compounds exhibited excellent detonation properties compared to AP (P: 15.8 GPa, Dv: 6368 m/s) and ADN (P: 23.6 GPa, Dv: 7860 m/s). Compound 13 has good density (1.90 g/ cm3) and moderate thermal stability (Td = 157 °C). Such a high thermal stability is unusual for polynitro compounds, which have a positive oxygen balance (+15.3%), and suggests 13 may be a promising high energetic density oxidizer comparable to AP and ADN. The oxygen content of 13 (52%) is better than that of ADN (45%), and its combined N + O content is 87%, significantly superior to AP (65%), indicating 13 could be a green high energetic density oxidizer. Specific impulse (Isp) is an extremely important parameter for determining the efficiency of a propellant. The higher the specific impulse of a propellant, the more efficient as it produces a greater thrust per unit of propellant. Due to its positive oxygen balance (+15.3%) and heat of formation, 13 has a much higher specific impulse (Isp = 238 s) value than AP (Isp = 157 s) and ADN (Isp = 202 s) as calculated using isobaric combustion conditions at a chamber pressure of 7 MPa bar versus ambient pressure with equilibrium expansion conditions at the nozzle throat by EXPLO5 (version 6.01).13 The specific impulse of a mixture of 13 with 12% aluminum was increased to 258 s, which is higher than that of AP and ADN mixed with the same amount of aluminum (230 and 253.7 s), demonstrating that 13 is very competitive. The values of the impact and friction sensitivities were obtained by using a BAM drop hammer apparatus and BAM friction tester, respectively. Compound 13 shows acceptable values for impact and friction sensitivity (IS: = 4 J, FS: = 120 N), which are similar to ADN (IS: = 3−5 J, FS: = 62−74 N). In summary, the cyano group can be transformed into a trinitro moiety by sequential nitration. When a molecule contains both acetonyl and chloroxime groups, a polynitro compound can be synthesized in a two-step nitration; nitrating first with TFAA/HNO3 and then with a mixture of H2SO4 and HNO3. 1,3-Bis(trinitromethyl)-1,2,4-triazole (13) was obtained using this two-step nitration method and fully characterized with various spectroscopic techniques, elemental analyses, and crystal structure. On the basis of the X-ray structure, 13 has a high density of 1.900 g cm−3 at room temperature. Additionally, 13 possesses an excellent physical performance and has promising applications as a high-energydensity oxidizer material for use as a practical replacement for AP and ADN in solid rocket propellant formulations for use in a variety of civilian, scientific, space, and military projects.
Letter
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.8b04114. Synthesis, characterization data, calculation details, and crystallographic data (PDF)
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Jean’ne M. Shreeve: 0000-0001-8622-4897 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by the Office of Naval Research (N00014-16-1-2089) and the Defense Threat Reduction Agency (HDTRA 1-15-1-0028). We are also grateful to the Murdock Charitable Trust, Vancouver, WA (Reference No. 2014120:MNL:11/20/2014), for funds supporting the purchase of a 500 MHz nuclear magnetic resonance spectrometer. We thank Professor Muhamed Sućeska of University of Zagreb for checking the specific impulse values.
■
REFERENCES
(1) Vogt, H.; Balej, J.; Bennett, J. E.; Wintzer, P.; Sheikh, S. A.; Gallone, P. Ullmann’s Encyclopedia of Industrial Chemistry; WileyVCH, 2002. (2) Agrawal, J. P. High Energy Materials: Propellants, Explosives and Pyrotechnics, 1st ed.; Wiley-VCH: Weinheim, 2010. (3) Madyakin, F. P. Components and Combustion Products of Pyrotechnic Compositions; KGTU: Kazan, 2006; Vol. 1. (4) Sijimol, M. R.; Jyothy, S.; Pradeepkumar, A. P.; Chandran, M. S. S.; Ghouse, S. S.; Mohan, M. Environ. Forensics 2015, 16, 125−134. (5) (a) Klapötke, T. M.; Gökcinar, E. Turk. J. Chem. 2010, 34, 953− 967. (b) Klapötke, T. M.; Krumm, B.; Scharf, R. Eur. J. Inorg. Chem. 2016, 2016, 3086−3093. (c) Klapötke, T. M.; Krumm, B.; Moll, R.; Rest, S. F. Z. Anorg. Allg. Chem. 2011, 637, 2103−2110. (d) Gidaspov, A. A.; Zalomlenkov, V. A.; Bakharev, V. V.; Parfenov, V. E.; Yurtaev, E. V.; Struchkova, M. I.; Palysaeva, N. V.; Suponitsky, K. Yu; Lempert, D. B.; Sheremetev, A. B. RSC Adv. 2016, 6, 34921−34934. (e) Dalinger, I. L.; Vatsadze, I. A.; Shkineva, T. K.; Kormanov, A. V.; Struchkova, M. I.; Suponitsky, K. Yu.; Bragin, A. A.; Monogarov, K. A.; Sinditskii, V. P.; Sheremetev, A. B. Chem. - Asian J. 2015, 10, 1987−1996. (f) Kettner, M. A.; Klapötke, T. M. Chem. Commun. 2014, 50, 2268−2270. (g) Kettner, M. A.; Karaghiosoff, K.; Klapötke, T. M.; Suceska, M.; Wunder, S. Chem. - Eur. J. 2014, 20, 7622−7631. (h) Semenov, V. V.; Shevelev, S. A.; Bruskin, A. B.; Shakhnes, A. Kh.; Kuz’min, V. S. Chem. Heterocycl. Compd. 2017, 53, 728−732. (6) (a) Nagamachi, M. Y.; Oliveira, J. I. S.; Kawamoto, A. M.; Dutra, R. C. L. J. Aerosp. Technol. Manage. 2009, 1, 153−160. (b) Mandal, A. K.; Kunjir, G. M.; Singh, J.; Adhav, S. S.; Singh, S. K.; Pandey, R. K.; Bhattacharya, B.; Kantam, M. L.; Kumar, K. V. Cent. Eur. J. Energy Mater. 2014, 11, 83−97. (c) Jadhav, H. S.; Talawar, M. B.; Dhavale, D. D.; Asthana, S. N.; Krishnamurthy, V. N. Indian J. Chem. Technol. 2005, 12, 187−192. (d) Dendage, P. S.; Sarwade, D. B.; Asthana, S. N.; Singh, H. J. Energ. Mater. 2001, 19, 41−78. 4 (e) Da Silva, G.; Rufino, S. C.; Iha, K. J. Aerosp. Technol. Manage. 2013, 5, 139−144. (f) Joo, Y.-H.; Min, B. S. New J. Chem. 2014, 38, 50−54. (7) (a) Thottempudi, V.; Gao, H.; Shreeve, J. M. J. Am. Chem. Soc. 2011, 133, 6464−6471. (b) Vo, T. T.; Parrish, D. A.; Shreeve, J. M. J. D
DOI: 10.1021/acs.orglett.8b04114 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters Am. Chem. Soc. 2014, 136, 11934−11937. (c) Axthammer, Q. J.; Krumm, B.; Klapötke, T. M. J. Org. Chem. 2015, 80, 6329−6335. (d) Zhao, X. X.; Li, S. H.; Wang, Y.; Li, Y. C.; Zhao, F. Q.; Pang, S. P. J. Mater. Chem. A 2016, 4, 5495−5504. (e) Fischer, D.; Klapötke, T. M.; Stierstorfer, J. Chem. Commun. 2016, 52, 916−918. (8) (a) Zhang, J.; Dharavath, S.; Mitchell, L. A.; Parrish, D. A.; Shreeve, J. M. J. Am. Chem. Soc. 2016, 138, 7500−7503. (b) Yin, P.; Parrish, D. A.; Shreeve, J. M. J. Am. Chem. Soc. 2015, 137, 4778− 4786. (c) He, C.; Yin, P.; Mitchell, L. A.; Parrish, D. A.; Shreeve, J. M. Chem. Commun. 2016, 52, 8123−8126. (d) Kumar, D.; Imler, G. H.; Parrish, D. A.; Shreeve, J. M. Chem. - Eur. J. 2017, 23, 1743−1747. (e) Fischer, D.; Klapötke, T. M.; Stierstorfer, J.; Szimhardt, N. Chem. Eur. J. 2016, 22, 4966−4970. (9) He, C.; Shreeve, J. M. Angew. Chem. 2016, 128, 782−785; Angew. Chem., Int. Ed. 2016, 55, 772−775. (10) (a) He, C.; Zhao, G.; Hooper, J. P.; Shreeve, J. M. Inorg. Chem. 2017, 56 (21), 13547−13552. (b) Zhao, G.; Kumar, D.; He, C.; Hooper, J. P.; Imler, G. H.; Parrish, D. A.; Shreeve, J. M. Chem. - Eur. J. 2017, 23, 16753−16757. (11) (a) Spackman, M. A.; McKinnon, J. J. CrystEngComm 2002, 4, 378−392. (b) Spackman, M. A.; Jayatilaka, D. CrystEngComm 2009, 11, 19−32. (c) Zhang, C.; Xue, X.; Cao, Y.; Zhou, Y.; Li, H.; Zhou, J.; Gao, T. CrystEngComm 2013, 15, 6837−6844. (12) Zhang, J.; Zhang, Q.; Vo, T. T.; Parrish, D. A.; Shreeve, J. M. J. Am. Chem. Soc. 2015, 137, 1697−1704. (13) Sućeska, M. EXPLO5, 6.01; Brodarski Institure: Zagreb, Croatia, 2013.
E
DOI: 10.1021/acs.orglett.8b04114 Org. Lett. XXXX, XXX, XXX−XXX
