Synthesis and properties of gem-dinitro energetic salts based on 1,2,4-oxadiazole with low impact sensitivity

Article abstract of DOI:10.1039/d0nj05530a

Eight energetic salts with a gem-dinitro group based on 1,2,4-oxadiazole were developed. All of the structures were confirmed by infrared (IR) spectroscopy, 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, and high-resolution mass spectrometry (HRMS), and single-crystal X-ray diffraction was used to determine the structures of the pivotal intermediate 3-(chlorodinitromethyl)-5-methyl-1,2,4-oxadiazole (3), the potassium salt (4) and the hydrazinium salt (7). All of them are insensitive to impact (>40 J) and have higher energy levels than trinitrotoluene (TNT). This journal is

Full text of DOI:10.1039/d0nj05530a

NJC
View Article Online
View Journal | View Issue
COMMUNICATION
Synthesis and properties of gem-dinitro energetic
salts based on 1,2,4-oxadiazole with low impact
sensitivity†
Cite this: New J. Chem., 2021,
45, 526
Received 11th November 2020,
Accepted 12th December 2020
a
Tian Lu,a Yuna He,
and Fu-Xue Chen
Jia Song,a Zhengwen Hou,a Hongquan Yin,a Guijuan Fanb
a
*
DOI: 10.1039/d0nj05530a
rsc.li/njc
Eight energetic salts with a gem-dinitro group based on 1,2,4- acidic hydrogen atom of dinitromethylene leads to hygroscopi-
oxadiazole were developed. All of the structures were confirmed city; (b) their ionic salts generally show high sensitivity; (c)
by infrared (IR) spectroscopy, 1H and 13C nuclear magnetic reso- some synthetic routes to them are not cost effective. On the
nance (NMR) spectroscopy, and high-resolution mass spectrometry contrary, trinitrotoluene (TNT) is deservedly the oldest and
(HRMS), and single-crystal X-ray diffraction was used to determine most common secondary explosive for multifarious applica-
the structures of the pivotal intermediate 3-(chlorodinitromethyl)- tions owing to its insensitivity to mechanical stimuli.11 Thus,
5-methyl-1,2,4-oxadiazole (3), the potassium salt (4) and the hydra- for application, it is meaningful to reduce the sensitivity of
zinium salt (7). All of them are insensitive to impact (440 J) and gem-dinitro compounds while at the same time maintaining a
have higher energy levels than trinitrotoluene (TNT).
higher energy level than TNT.
Our group has been working on high-energy insensitive
As the energy sources for the initial launch of and terminal materials for over ten years12 and we first reported an insensitive
damage by weapon systems, energetic materials have important explosive based on 1,2,4-oxadiazole.13 Follow-up studies have
military value and strategic significance.1 In order to improve proved that the 1,2,4-oxadiazole ring is an insensitive energetic
the efficiency and destruction capabilities of weapons, backbone,14 which encouraged us to still choose 1,2,4-
researchers have focused on developing high-energy materials oxadiazole as the energetic backbone. In this work, we successfully
over the years2 and have explored two key strategies. Optimization constructed insensitive gem-dinitro derivatives based on 1,2,4-
of the molecular structure, especially the planar stacking, is a oxadiazole (Scheme 1).
hot topic in improving the performance.3 However, a higher
number of nitro groups should be incorporated in these
materials because of the better detonation properties of nitrogen-
and oxygen-rich compositions, such as those of CL-20, which
contains six nitro groups, and octanitrocubane (ONC), which has
eight nitro groups.4 A common and more readily accessible
strategy is introducing a dinitromethyl group to various back-
bones, such as 1,3,4-oxadiazole,5 furoxan,6 pyrazole,7 triazole,8
tetrazole,9 and 1,2,4-oxadiazole.10
However, it is a pity that most gem-dinitro compounds are
far from suitable for real applications, even with their attractive
energy, as a result of the following notable drawbacks: (a) the
a School of Chemistry & Chemical Engineering, Beijing Institute of Technology
(Liangxiang Campus), No. 8 Liangxiang East Road, Fangshan district,
Beijing 102488, China. E-mail: fuxue.chen@bit.edu.cn
b Institute of Chemical Materials, CAEP, Mianyang 621050, China
† Electronic supplementary information (ESI) available: Details of computations,
data of single-crystal X-ray diffraction, copies of spectra. CCDC 2018730, 2038764
Scheme 1 Previous energetic materials with gem-dinitro groups and this
work.
and 2018495. For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/d0nj05530a
526 | New J. Chem., 2021, 45, 526--529
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2021

View Article Online
Communication
NJC
Scheme 2 Synthetic routes for compounds 1–11.
The synthetic routes for compounds 1–11 are shown in
Scheme 2. The initial reactant diaminoglyoxime was synthesized
according to the literature.15 N0-Hydroxy-3-carboximidamide-5-
methyl-1,2,4-oxadiazole (1) was prepared by cyclization with
triethyl orthoacetate under the catalysis of BF3ꢀEt2O giving a
white solid in 93% yield, following a reported procedure.16 After
diazotization and chlorination of 1, 3-carbimidoyl chloride-5-
methyl-1,2,4-oxadiazole (2) was obtained in a yield of 85%. Direct
nitration of 2 with fuming HNO3 and trifluoroacetic acid anhy-
dride (CF3CO)2O produced gem-dinitro-containing 3-(chlorodi-
nitromethyl)-5-methyl-1,2,4-oxadiazole (3) as a white solid in a
moderate yield of 43% with the optimal reaction time of 8 h (see
the ESI†). Significantly, we obtained a single crystal of 3 for X-ray
diffraction, which has been rarely reported in analogical works
Fig. 1 (a) X-ray crystal structure of 3; (b) packing diagram of 3; (c) X-ray
crystal structure of 4; (d) packing diagram of 4; (e) X-ray crystal structure of
7; and (f) packing diagram of 7.
and usually the nitration product of chloroxime was used directly crystal density of 1.799 g cmꢁ3 at 296 K (CCDC 2018730†). The
as an intermediate without any further characterization.6–10 plane of N(3)–N(4)–Cl(1) and the plane of oxadiazole are almost
Potassium (5-methyl-1,2,4-oxadiazol-3-yl)dinitromethanide (4) perpendicular, with a dihedral angle of 88.561, which leads to a
was easily prepared by the treatment of 3 with KI in methanol, cross 1D structure.17 Generally, a planar configuration is
with a yield of 85%. Subsequently, 4 was acidified by 2 M HCl expected to give a better density, but to our surprise, 3 still
and extracted with ethyl acetate to obtain a yellow oil, which has a better density of 1.799 g cmꢁ3 compared to other
was put into ammonium in methanol to afford a yellow solid compounds owing to its more compact stacking structure via
that was identified as ammonium (5-methyl-1,2,4-oxadiazol-3-yl)- head-to-tail assembly. This special head-to-tail assembly not
dinitromethanide (5), to give a yield of 81%. Similarly, the ionic only economizes space to improve density but also facilitates
salts 6–9 were also derived from 4 using the corresponding more hydrogen bonds between the methyl group (head) and the
nitrogen-rich bases (hydroxylamine, hydrazine, 3-amino-1,2,4- oxygen of the NO2 group (tail), which greatly reduces the
triazole, carbohydrazide) in methanol by taking advantage of the sensitivity (Fig. 1b).18 As expected, the impact sensitivity of 3
difference in acidity while aminoguanidinium (10) and guanidi- is over 40 J.
nium (11) were synthesized from aminoguanidine bicarbonate
The potassium salt of 4 crystallizes in the orthorhombic
and guanidine carbonate, respectively, with the release of carbon space group Pbca with a density of 1.864 g cmꢁ3 based on
dioxide facilitating the reaction. The yields of the above reactions crystal data (CCDC 2038764†). It is worth pointing out that the
were between 65 and 86%.
K atoms have three different coordination modes. In Fig. 1c,
All compounds were characterized by FT-IR and 1H and 13C K(1) is chelated by six oxygen atoms while K(2) and K(3) are
NMR spectroscopy together with HRMS (see the ESI†). A single chelated by five oxygen atoms. The average K–O distance is
crystal of 3 suitable for X-ray diffraction was obtained for the first 2.77 Å, which is shorter than those in previous reports,19
time by dissolving it in a mixture of petroleum ether (PE) and ethyl especially K(3)–O, which is just 2.75 Å. In turn, there are also
acetate (EtOAc) and evaporating slowly at 4 1C while single crystals three types of 1,2,4-oxadiazole, whose dihedral angles with the
of compounds 4 and 7 were obtained by slow evaporation of 4 and 7 plane of dinitromethylene are 71.191, 80.001 and 51.051, respec-
in MeOH/H2O at ambient temperature. The selected data and tively. Thus, an interesting three-dimensional metal–organic
structure refinement details of the crystals are presented in the ESI.† framework (3D MOF) was formed, as presented in Fig. 1d, and
The structure of the vital intermediate 3 is shown in Fig. 1a different parallels were formed by the ordered coordination of
and it crystallizes in the monoclinic space group P21/c with a different potassium atoms in the a-axis.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2021
New J. Chem., 2021, 45, 526--529 | 527

View Article Online
NJC
Communication
Table 1 Physical properties and detonation performance of 3–11
rb [g cmꢁ3
]
DHfc [KJ molꢁ1
]
Dd [m sꢁ1
]
Pe [GPa]
IS f [J]
FSg [N]
OBh [%]
a
Compd.
Td [1C]
i
3
—
1.799
—
—
—
—
—
—
4
5
6
7
8
9
178
161
146
166
108
137
147
185
295
1.864i
1.674
1.696
1.670i
1.677
1.668
1.653
1.680
1.650
ꢁ198.6
ꢁ71.9
ꢁ25.8
81.2
163.3
4.0
7125
8002
8239
8245
7845
8084
7920
7861
6881
21.192
25.155
28.419
26.643
23.327
24.788
23.071
22.917
19.5
440
440
440
440
440
440
440
440
15
160
240
160
144
324
240
160
144
—
ꢁ3.5
ꢁ19.5
ꢁ10.9
ꢁ21.8
ꢁ29.4
ꢁ23
10
11
TNTj
1.9
ꢁ30.5
ꢁ29.1
ꢁ25
ꢁ98.8
ꢁ67
a
b
c
Decomposition temperature (onset, DSC, 10 1C minꢁ1). Density (calculated using Gaussian09). Heat of formation (calculated using
d
e
f
Gaussian09). Detonation velocity (calculated with Explo5 v6.01). Detonation pressure (calculated with Explo5 v6.01). Impact sensitivity
g
h
(BAM method). Friction sensitivity (BAM method). Oxygen balance (based on CO) for CaHbOcNd, 1600(c ꢁ a ꢁ b/2)/MW (MW = molecular weight).
i
j
Crystal density. Ref. 20.
1
Hydrazinium 7 crystallizes in the monoclinic space group P21/c fully characterized by IR, H and 13C NMR, and HRMS, as well
with four molecules per unit cell with a density of 1.670 g cmꢁ3 as single-crystal X-ray diffraction for 3, 4 and 7. At the same
(CCDC 2018495†). The dihedral angle between the plane of time, DSC and sensitivity tests towards impact and friction
N(4)–N(5)–C(4) and oxadiazole is 88.271 (Fig. 1e). As shown in were carried out. The single crystal of 3 was used to confirm the
Fig. 1f, owing to the hydrogen atoms of the methyl and structure of the intermediate for the first time while the single
hydrazinium groups, lots of intermolecular hydrogen bonds crystal of 4 gave the structure of the 3D MOF. Moreover, the
are observed. The two strongest intermolecular hydrogen energetic salts show satisfactory impact sensitivity, good explo-
bonds are O(3)–H(7B) and O(2)–H(7A) with lengths of 2.10 Å sive performance and acceptable friction sensitivity. Compound
and 2.21 Å and angles of 151.181 and 144.031, respectively. The 7 decomposes at 166 1C with a detonation pressure of 26.6 GPa
other hydrogen bonds are relatively weak with lengths of 2.63 Å and a detonation velocity of 8245 m sꢁ1, which could be a
to 2.99 Å and angles of 1201 to 1701.
potential practical energetic material like TNT. In combination
The physical properties and thermodynamic behaviour of with 5-methyl-1,2,4-oxadiazol, gem-dinitro-derived energetic
4–11 are shown in Table 1. Thermal stability was measured using salts demonstrate amazing low sensitivity with the thermal
differential scanning calorimetry (DSC) at a rate of 10 1C minꢁ1
.
stability regulated by different cations, which gives new insight
The materials decomposed from 108 to 178 1C without melting, into gem-dinitro-derived compounds.
which proves that the cations can regulate the thermal stability
of the energetic salts.
Conflicts of interest
The mechanical sensitivity, comprising impact and friction
sensitivity, was examined using the standard BAM method. The
impact sensitivities of 4–11 are all over 40 J despite the presence
There are no conflicts to declare.
of the gem-dinitro group. To the best of our knowledge, there
are almost no cases of energetic potassium salts with an impact
Acknowledgements
sensitivity of over 40 J.21 According to its crystal structure, 4 is a
The National Natural Science Foundation of China (21772011)
financially supported this work.
relatively firm 3D MOF owing to the stronger interaction of K–O
and the hydrogen bonds. Moreover, methylene internal rota-
tion can also absorb impact force.
Notes and references
The densities and the heats of formation (HOF) of 4–11 were
calculated by using Gaussian0922 (see the ESI†) and then the
detonation velocity and pressure were predicted using EXPLO5
v6.01.23 For 4 and 7, we used their crystal densities directly. As a
result of the cross structure of (5-methyl-1,2,4-oxadiazol-3-yl)
dinitromethanide, the calculated densities for this series of
compounds range from 1.650 to 1.700 g cmꢁ3, while the
detonation velocities and pressures of 4–11 are higher than
those of TNT.
1 H. Gao and J. M. Shreeve, Chem. Rev., 2011, 111, 7377–7436.
2 Y. Qu and S. Babailov, J. Mater. Chem. A, 2018, 6, 1915–1940.
3 (a) Y. Wang, Y. Liu, S. Song, Z. Yang, X. Qi, K. Wang, Y. Liu,
Q. Zhang and Y. Tian, Nat. Commun., 2018, 9, 1–11;
(b) Y. Wang, S. Song, C. Huang, X. Qi, K. Wang, Y. Liu
and Q. Zhang, J. Mater. Chem. A, 2019, 7, 19248–19257;
(c) C. He, G. H. Imler, D. A. Parrish and J. M. Shreeve,
J. Mater. Chem. A, 2018, 6, 16833–16837; (d) G. Wang, T. Lu,
G. Fan, C. Li, H. Yin and F. Chen, Chem. – Asian J., 2018, 13,
3718–3722.
Conclusions
4 (a) S. Dharavath, J. Zhang, G. H. Imler, D. A. Parrish and
J. M. Shreeve, J. Mater. Chem. A, 2017, 5, 4785–4790;
We have developed a new series of energetic salts based on
1,2,4-oxadiazole with a gem-dinitro group. All compounds were
¨
(b) T. M. Klapotke, N. Mayr, J. Stierstorfer and
528 | New J. Chem., 2021, 45, 526--529
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2021

View Article Online
Communication
NJC
M. Weyrauther, Chem. – Eur. J., 2014, 20, 1410–1417; 17 J. Ma, J. Zhang, G. H. Imler, D. A. Parrish and J. M. Shreeve,
(c) T. Lu, C. Wang, G. Wang, S. Wang, J. Song, H. Yin, Org. Lett., 2020, 12, 4771–4775.
G. Fan and F. Chen, New J. Chem., 2019, 43, 13330–13333; 18 L. Meng, Z. Lu, Y. Ma, X. Xue, F. Nie and C. Zhang, Cryst.
(d) J. Zhang, S. Dharavath, L. A. Mitchell, D. A. Parrish and
J. M. Shreeve, J. Am. Chem. Soc., 2016, 138, 7500–7503.
5 J. Tian, H. Xiong, Q. Lin, G. Cheng and H. Yang, New
J. Chem., 2017, 41, 1918–1924.
6 C. He and J. M. Shreeve, Angew. Chem., Int. Ed., 2016, 55,
772–775.
Growth Des., 2016, 16, 7231–7239.
19 M. Zhang, W. Fu, C. Li, H. Gao, L. Tang and Z. Zhou, Eur.
J. Inorg. Chem., 2017, 2883–2891.
20 F. H. Allen, O. Kennard, D. G. Watson, L. Brammer,
A. G. Orpen and R. Taylor, J. Chem. Soc., Perkin Trans. 2,
1987, S1–S19.
7 C. Lei, H. Yang and G. Cheng, Dalton Trans., 2020, 49, 21 (a) C. He and J. M. Shreeve, Angew. Chem., Int. Ed., 2016, 55,
1660–1667.
772–775; (b) Y. Tang, H. Gao, L. A. Mitchell, D. A. Parrish
and J. M. Shreeve, Angew. Chem., Int. Ed., 2016, 55,
1147–1150; (c) Q. Zhang, D. Chen, D. Jing, G. Fan, L. He,
H. Li, W. Wang and F. Ni, Green Chem., 2019, 21, 1947–1955;
(d) W. Fu, B. Zhao, M. Zhang, C. Li, H. Gao, J. Zhang and
Z. Zhou, J. Mater. Chem. A, 2017, 5, 5044–5054; (e) Y. Liu,
C. He, Y. Tang, G. H. Imler, D. A. Parrish and J. M. Shreeve,
Dalton Trans., 2018, 47, 16558–16566.
8 H. Gu, Q. Ma, S. Huang, Z. Zhang, Q. Zhang, G. Cheng,
H. Yang and G. Fan, Chem. – Asian J., 2018, 13, 2786–2790.
9 T. M. Klapotke and F. X. Steemann, Propellants, Explos.,
¨
Pyrotech., 2010, 35, 114–129.
10 (a) C. Yan, K. Wang, T. Liu, H. Yang, G. Cheng and
Q. Zhang, Dalton Trans., 2017, 46, 14210–14218;
(b) Y. Tang, C. He, G. H. Imler, D. A. Parrish and
J. M. Shreeve, Chem. – Eur. J., 2017, 23, 16401–16407.
11 H. Gao, Q. Zhang and J. M. Shreeve, J. Mater. Chem. A, 2020,
8, 4193–4216.
12 (a) Z. Fu, R. Su, Y. Wang, Y. F. Wang, W. Zeng, N. Xiao,
Y. Wu, Z. Zhou, J. Chen and F.-X. Chen, Chem. – Eur. J.,
2012, 18, 1886–1889; (b) Y. Gao, L. Zhao, F. Pang, X. Qi,
J. Huang and F.-X. Chen, Chin. Chem. Lett., 2016, 27,
433–436; (c) F. Pang, G. Wang, T. Lu, G. Fan and F.-X.
Chen, New J. Chem., 2018, 42, 4036–4044.
22 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin,
V. N. Staroverov, R. Kobayashi, J. Normand,
K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
13 Z. Fu, C. He and F.-X. Chen, J. Mater. Chem. A, 2012, 22,
60–63.
14 (a) W. Hao, J. Zhang, C. He and J. M. Shreeve, Angew. Chem.,
Int. Ed., 2015, 54, 9367–9371; (b) Y. Tang, H. Gao,
L. A. Mitchell, D. A. Parrish and J. M. Shreeve, Angew. Chem.,
Int. Ed., 2016, 55, 3200–3203; (c) G. Zhao, C. He, P. Yin,
G. H. Imler, D. A. Parrish and J. M. Shreeve, J. Am. Chem.
Soc., 2018, 140, 3560–3563.
¨
J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas,
J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox,
Gaussian 09, Revision B.01, Gaussian, Inc., Wallingford CT,
2009.
15 E. C. Johnson, J. J. Sabatini and N. B. Zuckerman, Org.
Process Res. Dev., 2017, 21, 2073–2075.
´
16 V. G. Andrianov, V. G. Semenikhina and A. V. Eremeev, 23 M. Suceska, EXPLO5 v6.01, Brodarski Institute, Zagreb,
J. Heterocycl. Chem., 1994, 34, 475. Croatia, 2013.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2021
New J. Chem., 2021, 45, 526--529 | 529