Exploiting the energetic potential of 1,2,4-oxadiazole derivatives: Combining the benefits of a 1,2,4-oxadiazole framework with various energetic functionalities

Article abstract of DOI:10.1039/c7dt03320f

A series of 1,2,4-oxadiazole-derived energetic compounds were successfully synthesized using 1,2,4-oxadiazole-3-chloroxime as a versatile starting material. These energetic compounds were fully characterized by NMR spectroscopy, IR spectroscopy, and elemental analysis. The structures of compounds 5, 6a, 6c, 8 and 8a were determined by single crystal X-ray diffraction. The physicochemical and energetic properties of all the synthesized energetic compounds, including density, thermal stability and energetic performance (e.g., detonation velocities and detonation pressures) were investigated. Among these energetic compounds, hydrazinium salts 6b and 8b and hydroxylammonium salts 6c and 8c exhibit satisfactory calculated detonation performances, which outperform the commonly used high explosive RDX. Potassium salt 5 shows good detonation performance, high density as well as high sensitivity, making it a potential primary explosive. Compound 9 is a potential candidate for melt-cast explosives due to its remarkable liquid range between melting point (T_m = 98 °C) and decomposition temperature (T_d = 208 °C).

Full text of DOI:10.1039/c7dt03320f

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DOI: 10.1039/C7DT03320F
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ARTICLE
Exploiting the Energetic Potential of 1,2,4-Oxadiazole Derivatives:
Combining the Benefits of 1,2,4-Oxadiazole Framework with
Various Energetic Functionalities
Received 00th January 20xx,
Accepted 00th January 20xx
Chao Yana, Kangcai Wang,b Tianlin Liub, Hongwei Yang,a Guangbin Cheng*a, and Qinghua Zhang*b
DOI: 10.1039/x0xx00000x
A series of 1,2,4-oxadiazole-derived energetic compounds were successfully synthesized using the 1,2,4-oxadiazole-3-
chloroxime as a versatile starting material. These energetic compounds were fully characterized by NMR spectroscopy, IR
spectroscopy, and elemental analysis. The structures of compounds 5, 6a, 6c, 8 and 8a were determined by single crystal
X-ray diffraction. The physicochemical and energetic properties for all synthesized energetic compounds, including density,
thermal stability and energetic performance (e.g., detonation velocities and detonation pressures), were investigated.
Among these energetic compounds, hydrazinium salts 6b, 8b and hydroxylamonium salts 6c, 8c exhibit satisfactory
calculated detonation performances, which outperforms the commonly used high explosive RDX. Potassium salt 5 shows
good detonation performance, high density as well as high sensitivity, making it a potential primary explosive. Compound
www.rsc.org/
o
9 is a potential candidate for melt-cast explosives due to its remarkable liquid range between melting point (Tm = 98 C)
and decomposition temperature (Td = 208 oC).
variety of new energetic compounds have been designed and
synthesized based on versatile nitrogen-rich heterocyclic rings
like tetrazoles,4 1,2,4-triazoles,5 1,2,3-triazoles,6 pyrazoles,7
Introduction
Over the past decades, the design and synthesis of new
explosive compounds with excellent detonation performance
and low sensitivity are important goals in the field of energetic
materials.1 Typical high explosives including cyclo-,1,3,5-
trimethylene-2,4,6-trinitramine (RDX) and octahydro-1,3,5,7-
tetranitro-1,3,5,7-tetrazocine (HMX), which are widely used in
the military applications as secondary explosives today, lack
the low sensitivities of insensitive but lower detonation-
performing energetic materials like 2,4,6-triamino-1,3,5-
trinitrobenzene (TATB), 2,6-diamino-3,5-dinitropyrazine-1-
oxide (LLM-105), and 2,2-dinitroethene-1,1-diamine (FOX-7). 2
Although there have been numerous attempts to develop
potential high quality energetic materials with a fine balance
between high detonation level and low sensitivity, an inherent
trade-off between high energy and molecular stability makes
the discovery and development of high performing energetic
materials an interesting but challenging task.3
imidazoles,8 and furazans9. Due to the structural
characteristics of a large number of energetic N-N, C-N, and N-
O bonds in the backbone, these nitrogen-rich energetic
compounds usually have the higher nitrogen content,
enhanced heats of formation, and superior oxygen balance.
Within this context, a number of five- and six-membered
nitrogen heterocycles have been considered for the
development of new nitrogen-rich energetic materials.
Recently, 1,2,4-oxadiazole heterocycles have received growing
attentions as the key backbone of energetic nitrogen-rich
structures. 1,2,4-oxadiazole has demonstrated its promise for
the construction of new high explosives with balanced energy
and safety properties. In previous studies, Kayukova et al. 10
reviewed the synthesis of 3,5-substituted 1,2,4-oxadiazoles.
11
Fershtat et al.
proposed three synthetic strategies for
construction of the 1,2,4-oxadiazole framework. Recently,
Klapötke et al. 12,13 demonstrated that the combination of C-C
bond bridged 1,2,4-oxadiazoles with different energetic
moieties (gem-nitro, trinitromethyl and fluorodinitromethyl)
led to a good balance between high detonation performance
and low sensitivity for the resulting energetic materials. It is
obvious that the great potential of developing new 1,2,4-
oxadiazole-derived energetic materials has not fully exploited
yet. In comparison with single 1,2,4-oxadiazole ring, the
coupled heterocyclic ring-based energetic compounds
containing the 1,2,4-oxadiazole backbone are expected to
have better thermal and molecular stability, higher heats of
formation, and superior detonation performance. However,
In recent years, nitrogen-rich compounds have received
significant interest in the design of new energetic materials. A
a.School of Chemical Engineering, Nanjing University of Science and Technology,
Xiaolingwei 200, Nanjing, Jiangsu, China. E-mail: gcheng@mail.njust.edu.cn
b.Research Center of Energetic Material Genome Science, Institute of Chemical
Materials, China Academy of Engineering Physics (CAEP), Mianyang, 621900, P. R.
China. E-mail: qinghuazhang@caep.cn
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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ARTICLE
Journal Name
2OH.HCl
2OH.HCl
H2N
NH2
O
H
O
H
NH
NH
the synthetic methods of energetic compounds featuring the
coupled heterocyclic frameworks of 1,2,4-oxadiazole and
tetrazole or furoxan has not been fully established, and studies
on diverse functionalization strategies towards these coupled
1,2,4-oxadiazole-based heterocycles also have great potential
to be exploited.
View Article Online
N
N
DOI: 10.1039/C7DT03320F
NaOH, 90oC
HO
OH
NaOH, 0oC
N
N
HO
OH
1
BF3.Et
2O
HC(OEt)3
N
Cl
N
NH2
N
HCl
In a continuing effort to develop new energetic compounds
with high detonation performance, less sensitivity and eco-
friendly feature, in this work our interest focused on the
design and synthesis of a series of new 1,2,4-oxadiazole-based
energetic compounds with various functionalities. In the
synthetic methodology of these new energetic 1,2,4-
oxadiazoles, 1,2,4-oxadiazole-3-chloroxime demonstrated its
promising potential as a versatile platform compound for the
efficient construction of the target energetic molecules with
various energetic functionalities or in combination with
different heterocycles with high heats of formation (i.e.,
hydroxytetrazole and furoxan). The preparation of several
nitrogen-rich 1,2,4-oxadiazole-based energetic salts from was
also presented. All the obtained energetic compounds were
fully characterized by IR, multinuclear NMR spectroscopy,
elemental analysis, and DSC. The structures of part compounds
were determined by single crystal X-ray diffraction. The
thermal stability, mechanical sensitivities, as well as the
theoretical detonation performance for these 1,2,4-
oxadiazole-based energetic compounds were also investigated
or calculated.
O
O
N
NaNO2
N
N
OH
OH
3
2
CCO)2O
(F3
NO2
NO2
N
NO2
Cl
NO2
N
NO2
NO2
HO
N
N
100%HNO3
HCCl3
HCl
O
KI
K
O
N
O
N
4
6
5
N3
N
N
N
N
N
N
3
O
N
NaN3
HCl
O
N
N
OH
8
7
O
O
N
N
N
K
2CO3
N
O
N
N
O
9
Scheme 1. Synthesis of 1,2,4-oxazole derivatives.
NO2
NO2
N
N
base
NO2
NO2
N
N
Cat+
O
O
MeOH
6a-c
6
O
HO
base
N
N
N
N
Cat+
N
N
N
N
O
O
EtOH
N
N
8a-c
Results and discussion
N
N
8
Synthesis
=
Cat+
NH4
NH3NH2
Glyoxime and diaminoglyoxime
according to the literature.14,15 Diaminoglyoxime (
triethylorthoformic could cyclize into 1,2,4-oxadiazole-3-
carboxyamidoxime ( ) which finally formed 1,2,4-oxadiazole-3-
chloroxime (
) by the chlorination reaction16. Subsequently,
three different strategies were employed to convert
compound to new energetic compounds. First, 3-
dinitromethyl-1,2,4-oxadizole ( ) was readily produced from
the nitration of 1,2,4-oxadiazole-3-chloroxime with a mixture
of trifluoroacetic acid anhydride (TFAA) in HCCl3, followed by
treatment with KI in methanol and finally acidification with
diluted hydrochloric acid (Scheme 1). Second, 5-(1,2,4-
(
1
)
were synthesized
NH3OH
1
) and
c
a
b
Scheme 2. Synthetic route to the nitrogen-rich salts derived
from 6 and 8 using the corresponding nitrogen-rich bases
(ammonia, hydrazine, hydroxylamine).
2
3
3
6
properties are given and discussed.
Preparation of a series of energetic salts from compounds
and was accomplished by dissolving the neutral compounds
6
8
in methanol (or ethanol), followed by the addition of the
corresponding nitrogen-rich bases (Scheme 2). Owing to the
poor solubility of the target ionic molecules, the desired
energetic salts precipitated almost quantitatively with high
purities.
oxadiazolyl-3-yl)-1-hydroxytetrazole (8) was prepared by two-
step reactions including nucleophile substitution of chlorine
with azide and subsequent cyclization in the acidic conditions.
3-[4-(1,2,4-Oxadiazol-3-yl)-2-oxido-1,2,5-oxadiazol-3-yl]-1,2,4-
oxadiazole (9) was synthesized in one-step reaction through
direct cyclization of 1, 2,4-oxadiazole-3-chloroxime in the
Single Crystal X-ray Structure Analysis
presence of K2CO3. Despite 5-(1,2,4-oxadiazolyl-3-yl)-1-
S
ingle crystals of 5, 6a, 6c and 8a suitable for X-ray diffraction
17
hydroxytetrazole (
1,2,5-oxadiazol-3-yl]-1,2,4- oxadiazole
8
)
and 3-[4-(1,2,4-oxadiazol-3-yl)-2-oxido-
studies were all obtained from methanol/water by slow
evaporation of the solvents at ambient temperature. The single
crystal data of four compounds were collected at 173 K. The
crystallographic data and CCDC numbers for these compounds are
summarized in Table S1 (ESI†).
18
(9
)
have been
synthesized before, different approaches were used for the
synthesis of compound and compound 9, and their energetic
8
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(a)
ARTICLE
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DOI: 10.1039/C7DT03320F
(b)
(a)
(b)
(c)
(c)
(d)
Figure 1. a) the coordination environment of energetic ligand
in compound ; b) view of the layer structure contained in
compound ; c) the 3D structure of compound view along
[110] direction.
5
5
5
Figure 2. a) the asymmetrical unit of compound 6a; b) the
supramolecular interaction between energetic anion and
adjacent ammoniums; c) the 2D super-molecular structure
contained in compound 6a; d) the 3D super-molecular
structure of compound 6a. Dotted lines represent hydrogen
bonds.
3-Dinitromethyl-1,2,4-oxadizole potassium salt (5) crystallizes in
the triclinic space group P-1 with a high calculated density of
2.066 g cm-3 based on crystal data. Each energetic ligand is
connected to six potassium atoms via K-O bond (Figure 1a),
and the bond length of K-O falls in the range of 2.723(2)-
2.930(2) Å. In the energetic ligand, the dihedral angel between
the plane where gem-dinitromethyl group lies and the
oxadiazole ring plane is 89.84o. Each potassium atom is
coordinated to six oxygen atoms which are from five different
energetic ligands (Figure S1, ESI†). This connection mode gives
supramolecular interaction. And then, the layers are stacked in
an AAAA mode to build the 3D supramolecular structure of
compound 6a (Figure 2c).
Hydroxylammonium 3-dinitromethyl-1,2,4-oxadizole
(6c)
rise to the 3D framework of compound 5. This 3D framework
crystallizes in the triclinic space group P-1 with a crystal
density of 1.840 g cm-3 which is higher than that of 6a. It is
interesting that the structure of energetic ligand in 6c is much
can also been viewed as a pillared layered structure. As shown
in Figure 1b, adjacent potassium atoms are connected to each
other via oxygen atom to construct the infinite 1D linear
structure, and then the nearby 1D linear moieties are
connected each other to form the 2D layer structure via nitro
groups. Furthermore, the layers are pillared by energetic
different to that in compound 5. For instance, the dihedral
angel between the plane where gem-dinitromethyl group lies
and the oxadiazole ring plane is 74.21o but the dihedral angel
is 89.84o in compound
5. In the structure of 6c, each
ligands to construct the 3D framework of compound
1c). Regular 1D channels are contained in the 3D framework of
compound viewed along the [110] direction to further form
5 (Figure
hydroxylammonium cation is interacted with five energetic
ligands via strong hydrogen bonds (Figure 3c), i.e., N-H···O and
O-H···N. The distances of N···O is in the range of 2.757(2)-
3.043(1) Å. And each energetic ligand is connected with five
adjacent hydroxylammonium cations via hydrogen bonds
(Figure 3a), while the nearby energetic ligands are interacted
with each other (Figure 3b) via hydrogen bond of C-H···N and
the distance of C···N is 2.989 (2) Å. By virtue of those hydrogen
bonds, the 3D supramolecular structure of 6c is constructed
(Figure 3d). The very extensive hydrogen bond nets contained
in 6c may also explain its higher crystal density (1.840 g cm-3 of
6c) than that of 6a (1.734 g cm-3 of 6a).
5
the same 3D channels.
Single X-ray diffraction reveals that ammonium 3-
dinitromethyl-1,2,4-oxadizole (6a) crystallizes in the triclinic
space group P-1 with a high calculated crystal density of 1.734
g cm-3. One ammonium cation and one energetic anion are
contained in the asymmetrical unit of compound 6a (Figure 2a).
In the crystal structure of 6a, each energetic ligand is
connected to five adjacent ammonium cations via hydrogen
bonds of N-H···O (Figure 2b). The distance of N···O is in the
range of 2.870(2)-3.087(1) Å, while each ammonium cation is
connected to five energetic ligands via hydrogen bonds (Figure
S2, ESI†). A 2D layer structure is constructed by this
5-(1,2,4-Oxadiazolyl-3-yl)-1-hydroxytetrazole (
in the orthorhombic space group Pbca and one molecule is
8) crystallizes
contained in the asymmetric unit of
8
(Figure 4a). The crystal
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DOI: 10.1039/C7DT03320F
Figure 3. a) The supramolecular interaction between energetic
anion and adjacent hydroxylammoniums; b) the hydrogen
bonds between two nearby energetic anions; c) the
supramolecular interaction between hydroxylammonium and
nearby energetic anions; d) the 3D supramolecular structure of
compound 6c. Dotted lines represent hydrogen bonds.
Figure 5. a) The molecular structure of compound 8a; b) the
supramolecular interaction between energetic anions and
ammoniums; c) the supramolecular structure of compound 8a
;
d) dotted lines represent hydrogen bonds.
cm-3. In compound 8a, each ammonium cation is connected to
four adjacent energetic anions via hydrogen bonds of N-H···N
and N-H···O (Figure S3, ESI†). The distances of N···N and N···O
are in the range of 2.999 (2)-3.072(2) and 2.892(1)-2.961(1) Å,
respectively. Each energetic anion is connected to three
nearby ammoniums and two other energetic anions by
hydrogen bonds (Figure 5b). The 3D supramolecular structure
of compound 8a is constructed by very strong hydrogen bond
interactions (Figure 5c). The existence of these extensive
hydrogen bond nets in 8a may result in the relatively higher
density (1.714 g of 8a) than that of compound 8
(1.689 g cm-3).
Physicochemical and energetic properties
Figure 4. a) The molecule structure of compound
8
; b) the
wave-liked layer structure contained in compound
8
; c) the Thermal stability of all compounds were determined via DSC at
a heating rate of 5 C min-1 by using approximately 0.7 mg of
powdered sample. Compound starts to decompose at 165
oC, which is quite a bit lower than its potassium salt
with a
decomposition temperature of 170 oC. Interestingly, the
thermal decomposition temperatures of ammonium salt (6a
o
.
supramolecular interaction between the molecules of
compound ; d) the 3D supramolecular structure of compound
. Dotted lines represent hydrogen bonds.
6
8
5
8
,
density of this compound is 1.689 g cm-3. All the non-hydrogen
atoms in
are almost in a plane (N1-C2-C3-N3=-5.66o). The
140 oC), hydrazinum salt (6b, 132 oC) and hydroxylammonium
8
salt (6c, 156 oC) are slightly lower than that of compound
6
adjacent molecules are interacted with each other through
hydrogen bonds (i.e., O-H···N and C-H···N) (Figure 4c), and the
distances of O···N and C···N are 2.578 (2) and 3.224 (2) Å,
respectively. Each molecule is interacted with four adjacent
o
(165oC)(Figure 6a). Compound
8
starts to melt at 133 C and
decompose at 143 oC(Figure 6c), and its energetic salts 8a-c
demonstrate an enhanced thermal stability (Figure 6b). The
DSC curve of compound
9
has two endothermic peaks (Figure
begins
to melt at 98 C and then decompose at 208 C. Owing to
remarkable deviation between Tm and Td, compound can
molecules.
A wave-liked layer is formed through this
6d). In combination with TG curve, it can be seen that
9
supramolecular interaction (Figure 4c). These layers are
further stacked to form the 3D supramolecular structure of
(Figure 4d).
o
o
8
9
be considered as a potential candidate for melt-cast explosives.
The densities of as-synthesized compounds was measured
with helium gas pycnometer at 25 oC or calculated. Among
Ammonium 5-(1,2,4-Oxadiazolyl-3-yl)-1-hydroxytetrazolate
(8a) crystallizes in the monoclinic space group Cc with one
ammonium and one energetic anion contained in the
asymmetric unit (Figure 5a). The crystal density of 8a is 1.714 g
them, the densities of
6
(1.85 g cm-3), 6b (1.81 g cm-3), 6c (1.84
g cm-3) and
9
(1.82 g cm-3) exceed that of RDX (1.8 cm-1).
4 | J. Name., 2012, 00, 1-3
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ARTICLE
For safety testing, the sensitivity of each compound towards and friction sensitivity (FS) were determined using the
impact and friction was measured. The impact sensitivity (IS) standard BAM fall hammer and BDAOMI: 10f.1r0ic3Vt9iei/owCnA7rDtiTctl0ee3Os3tn2eli0nrFe,
Figure 6. a) DSC plots of compounds
6
and its energetic salts
5, 6a-c; b) DSC plots of energetic salts 8a-c; c) TG and DSC
plots of compounds
8
; d) DSC plots of compounds 9.
Table 1. Physicochemical and energetic properties of 1,2,4-oxadiazole-derived energetic compounds (5, 6, 6a-c, 8, 8a-c, and 9).
6
6a
6b
6c
5
8
8a
8b
8c
9
RDXo
Formula
C3H2N4
O5
174.07
C3H5N5
O5
191.10
C3H6N6
O5
206.12
C3H5N5
O6
207.10
C3H1N4O5 C3H2N6
C3H5N7
O2
171.12
C3H6N8
O2
186.14
C3H5N7
O3
187.12
C6H2N6
O4
222.12
C3H6N6
O6
222.12
K
O2
M/g mol-1
212.16
154.09
ISa/J
4
9
6
6
0.6
6
10
8
8
18
7
FSb/N
84
120
36.7
-29.3
-
144
40.8
-31.1
-
128
33.8
-19.3
-
36
72
120
57.30
-63.1
-
108
60.20
-68.8
-
96
120
120
37.8
-21.6
-
Nc/%
32.2
-18.4
-
26.4
-11.3
-
54.54
-51.9
133
143
1.69m
363
52.40
-47.0
-
37.84
-64.8
114
Ωd/%
Tme [°C]
Td . f/ °C
ρg/g cm–3
ΔfHmh/kJ mol-1
165
1.85n
-20.57
140
1.74m
-29.74
132
1.81n
118.82
156
1.84m
16.74
176
2.07m
-164.44
174
1.72m
322
152
1.71n
478
141
1.79n
372
214
1.82n
210
1.80
70
326
EXPLO5 V6.02values:
-ΔExU°i/ kJ kg–1
Tdetj/ K
5378
4134
2908
29.4
4476
3034
34.3
4848
3367
35.5
3040
2879
33.4
4995
3567
25.0
4829
2986
28.0
5362
3193
30.4
3733
2613
32.7
4956
3477
26.8
6125
4236
34.9
3824
32.3
8527
PCJk/GPa
Vdetl/m s-1
8301
8843
8793
8880
8037
8576
8929
8913
8043
8748
a Impact sensitivity (BAM drop hammer), b Friction sensitivity (BAM friction tester), c Nitrogen content, d Oxygen balance (Ω = (xO–2yC–1/2zH)M/1600, e Melting point,
f Temperature of decomposition, g Density, h Calculated energy of formation, i Energy of explosion, j Explosion temperature, k Detonation pressure, l Detonation velocity,
m Crystal density, n Measured density (gas pycnometer), o Taken from the literature22
.
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Journal Name
respectively. As given in Table 1, the neutral compound
ARTICLE
spectroscopy, elemental analysis, differentiVailew AsrtcicalenOnnilninge
6
shows high sensitivities towards impact and friction with IS calorimetry, and sensitivity tests towardDsOimI: 1p0a.1c0t39a/nCd7DfTr0ic3t3io20nF.
value of 4 J and FS value of 84 N, respectively. The potassium Their energetic properties including detonation velocity and
salt
5
has higher sensitivities (IS = 0.6 J, FS = 36 N). However, pressure were calculated with EXPLO5 (version 6.02). The
6a 6c and 8a were further
the mechanical sensitivities of the nitrogen-rich salts (6a-c) are structures of compounds
5
,
,
, 8
obviously improved. Especially, the sensitivities of ammonium determined by single crystal X-ray diffraction. The ionic
salt 6a (IS = 9 J, FS = 36 N) have a obvious reduction compared compounds 6a-c and 8a-c showed reduced sensitivities as
to their precursor
rich salts (8a-c) are also better than that of neutral compound much safer to handle since their stability towards friction and
. Remarkably, formation of the nitrogen-rich salts (6a-c and impact was considerably increased. The formation of rich-
8a-c) leads to a significant improvement in mechanical nitrogen energetic salts from
sensitivity, which may be attributed to extensive hydrogen- compounds or showed a positive influence on the
bonding interactions between the cation and the anion in salt. detonation performance of as-synthesized compounds, e.g.,
Compound has relative optional sensitivity property with IS their detonation velocities and pressures were both increased.
value up to 18 J. Of these 1,2,4-oxadiazole energetic materials, potassium salt
6. Similarly, the sensitivities of the nitrogen- compared to their neutral molecules, in which 6a and 8a were
8
6
8
9
5
The heats of formation of all compounds were calculated has the potential to be used as the primary explosive due to its
(for further details and results refer to the Supporting excellent explosive performance, high density as well as high
Information). To estimate the detonation performances of the sensitivity. Compound
prepared compounds, selected key parameters were explosives due to remarkable deviation between Tm (98 oC)
calculated with EXPLO5 (version 6.02)20 based on calculated and Td (208 oC). Moreover, both the hydrazinium salts (6b
8b
heats of formation and experimental densities. The and the hydroxylamonium salts (6c 8c) also exhibited good
9 is a potential candidate for melt-cast
,
)
,
physicochemical and energetic properties of obtained calculated detonation performances, which outperformed the
energetic compounds are summarized in Table 1. The commonly used high explosive RDX.
detonation pressure of all compounds lie in the range of 25.0
GPa (
8
) to 35.5 GPa (6c). The calculated detonation velocities
and its
for all materials are above 8000 m s–1. In despite of
8
Experimental section
ionic derivatives 8a-c with lower density, they exhibits good
explosive performance because of high positive heats of
formation (ΔfH). In particular, compound 8b has the ΔfH values
of 478 kJ mol-1, which are approximately nine times higher
than those of RDX (70 kJ g-1). The calculated detonation
Caution! Although we experienced no explosion in handling
these energetic materials, small scale and best safety practices
(leather gloves, face shield) are strongly encouraged
！
General methods
velocity of 6b
used explosive RDX with the value of 8748 m s–1. In
comparison to compounds and , a marked performance
increase of their nitrogen-rich ionic derivatives except for 6a is
seen. Potassium salt
(8880 m s–1) shows good explosive
performance due to its high density and high sensitivity, which
makes it a potential primary explosive. Compound shows
, 8b, 6c and 8c are higher than the commonly
All chemicals and solvents were obtained from Sigma-Aldrich
or Alfa-Aesar and were used as supplied. 1H and 13C NMR
spectra were recorded at 298 K using DMSO or D2O on Bruker
600AVANCE Spectrometer, operating at 600 and 151 MHz,
respectively. The chemical shifts are given relative to
tetramethylsilane as external standard. Densities were
measured at 25oC using on a Micromeritics AccupycII 1340 gas
pycnometer. Elemental analyses were obtained on an
Elementar Vario MICRO CUBE (Germany) elemental analyser.
The melting and decomposition points were recorded on
TGA/DSC Mettler Toledo calorimeter at a scan rate of 5 oC min-
1. Sensitivity data were determined using a BAM drophammer
and a BAM friction tester. Single crystal X-ray diffraction data
was collected on an Oxford Xcalibur3 diffratometer with Mo-
Kα radiation (λ=0.71073 Å) at low temperature. Detonation
velocity and detonation pressure data were calculated by
program package EXPLO5 (version 6.02).
6
8
5
9
lower detonation velocities and pressures than RDX, despite it
has much higher heats of formation and comparable densities.
Conclusions
In summary, a series of 1,2,4-oxadiazole energetic compounds
were designed and synthesized. In the synthetic strategy,
1,2,4-oxadiazole-3-chloroxime has demonstrated its promise
as a versatile starting material for the synthesis of the 1,2,4-
oxadiazole-derived energetic molecules with various
functionalities including gem-dinitromehyl group and
hydroxytetrazole (or furazan-oxide ring). Three neutral
energetic compounds including 3-dinitromethyl-1,2,4-
l,2,4-oxadiazole-3-carboxyamidoxime (2) and 1,2,4-oxadiazo-
le-3-chloroxime(3) were prepared according to the literature
procedures.16
3-dinitromethyl-1,2,4-oxadizole(6). Compound
3 (0.443 g, 3
oxadizole (
and 3-[4-(1,2,4-oxadiazol-3-yl)-2-oxido-1,2,5-oxadiazol-3-yl]-
1,2,4-oxadiazole were synthesized, respectively. The
6), 5-(1,2,4-Oxadiazolyl-3-yl)-1-hydroxytetrazole (8)
mmol) in CHCl3 (3 mL) was added dropwise to a stirred mixture
of trifluoroacetic acid anhydride(2.1 mL) and 100%HNO3 (1.2
mL), while maintaining the reaction temperature at 0~5 oC.
After the addition was complete, the ice bath was removed,
and the mixture was allowed to warm slowly to room
(9)
corresponding rich-nitrogen energetic salts 6a-c and 8a-c were
further prepared. All the as-synthesized energetic compounds
were fully characterized by IR, multinuclear NMR
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J. Name., 2013, 00, 1-3 | 6
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Dalton Transactions
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ARTICLE
temperature. It was stirred for another 2 h, and then poured 610 cm-1; elemental analysis calcd (%) for C3H5N5O6 (207.10): C
View Article Online
into ice water (50 mL) and extracted with CHCl2 (3×20 mL). The 17.40, H 2.43, N 33.82; found: C 17.27, HD2O.6I:510, .N103393/.C678D.T03320F
organic phases were combined, dried over magnesium sulfate, 3-[4-(1,2,4-oxadiazol-3-yl)-2-oxido-1,2,5-oxadiazol-3-yl]-1,2,4-
and then concentrated under vacuum to provide the oxadiazole(9). To a suspension of
3 (0.295 g, 2mmol) in Et2O
intermediate
4
as a colorless solid. Compound
4
was dissolved (10 mL) was added dropwise K2CO3 (0.157 g, 1.13 mmol) in
o
in methanol (10 mL), potassium iodide (0.349 g, 2.1 mmol) in water (4 mL) for 30 min. After stirring for 2 h at 10 C, the
methanol (5 mL) was added dropwise, and the mixture was resulting mother liquid was extracted with ethyl ether
stirred 3 h at room temperature. The precipitate formed was (2×20ml). The combined organic layer was dried over MgSO4,
collected by filtration and washed with methanol (5 mL) and and concentrated in vacuo to give a white solid (0.098 g,
ethyl ether (5 mL) to give
solid. To the suspension of potassium salt
5
(1.12 g, 30.2%) as a light-yellow 44%).1H NMR (600 MHz, DCCl3) : δH = 8.99 (1Н, s), 9.03 (1Н, s)
(1g, 4.7mmol) in ppm; 13C NMR (151MHz, DCCl3): δC = 105.59, 144.68, 156.13,
5
water (20ml) concentrated hydrochloride acid was added 158.23, 166.06, 166.10 ppm; IR (KBr): ν = 3118, 1610,1573,
dropwise in ice bath. Then extracted with ethyl acetate 1552, 1532, 1440, 1378, 1367, 1275, 1102, 1093, 1051, 1022,
(3×30mL). The organic phases were combined, dried over 956, 944, 907, 895, 823, 613 cm-1; elemental analysis calcd (%)
magnesium sulfate, and then concentrated under vacuum to for C7H4N6O3 (220.15): C 38.19, H 1.83, N 38.18, found: C
provide a yellow liquid. The yellow liquid was dissolved in 38.06, H 1.85, N 38.08.
methanol (5ml) and standed at ambient temperature for a day. 5-(1,2,4-Oxadiazolyl-3-yl)-1-hydroxytetrazole(8). A solution of
The solid formed was collected by filtration and washed with sodium azide (1.3 g, 20 mmol) in water (8 mL) was added
methanol (0.5 mL) and ethyl ether (5 mL) to give
6 (0.27 g, dropwise to a solution of 3 (2.31 g, 15 mmol) in ethanol (100
33%) as a yellow-green solid. 1H NMR (600 MHz, DMSO-d6): δH mL). The suspension was stirred at room temperature for 20 h
= 7.09 (1Н, s), 9.63 (1Н, s) ppm; 13C NMR (151 MHz, DMSO-d6): and subsequently poured into 2M HCl (400 mL). The clear
δC = 122.65, 162.64, 167.31 ppm; IR (KBr): ν = 3221, 3128, solution was extracted with ethyl acetate (4×100 mL), the
3073, 1553, 1521, 1498, 1469, 1428, 1363, 1346, 1271, 1185, combined organic phases were dried over magnesium sulfate
1150, 1103, 1085, 970, 958, 897, 884, 817, 752, 610, 459 cm-1; and the solvent was concentrated in vacuum and dry by air
elemental analysis calcd (%) for C3H2N4O5 (174.07): C 20.70, H flow to 1,2,4-oxadizole-3-azidoxime (
7
) as a colorless powder
1.16, N 32.19; found: C 20.55, H 1.18, N 32.04. (2.08 g, 90%). A solution of
7
(2.08 g, 13.5mmol) in
General procedures for the preparation of energetic salts 6a-c. concentrated hydrochloric acid (50 mL) was stirred at room
Ammonia (25 wt% in water, 2.5mmol), hydrazine hydrate (80 temperature for 12 h. The clear solution was poured on ice
wt% in water, 2.1 mmol) or hydroxylamine (50 wt% in water, and extracted with ethyl acetate (3×100 mL). The combined
2.1 mmol) was added to a solution of 3-dinitromethyl-1,2,4- organic phases were dried over magnesium sulfate and the
oxadizole
6
(0.348 g, 2 mmol) in methanol (5 mL). After stirring solvent was solvent was concentrated in vacuum and dry by air
1
for 2h at ambient temperature, the precipitate was collected flow to yield a colorless powder (1.98 g, 95%). H NMR (600
by filtration and washed with MeOH and Et2O.
Ammonium 3-dinitromethyl-1,2,4-oxadizole 6a).
MHz, DMSO-d6): δH = 7.08 (1Н, s), 9.9 (1Н, s) ppm; 13C NMR
(151 MHz, DMSO-d6): δC = 137.95, 156.82, 168.66 ppm; IR
(
6a (0.248 g, 65%) a light yellow solid. 1H NMR (600 MHz, (KBr): ν = 3120, 1532, 1407, 1351, 1313, 1285, 1257, 1190,
DMSO-d6): δH = 7.04 (4Н, s), 9.57 (1Н, s) ppm; 13C NMR (151 1133, 1098, 1061, 975, 961, 928, 913, 756, 743, 729, 709, 669,
MHz, DMSO-d6): δC = 122.64, 162.57, 167.20 ppm; IR (KBr): ν = 613, 551, 412 cm-1;
3212, 3128, 3080, 2859, 1553, 1520, 1498, 1464, 1428, 1360, elemental analysis calcd (%) for C3H2N6O2 (154.09): C 23.38, H
1346, 1271, 1185, 1150, 1103, 1085, 970, 958, 897, 884, 817, 1.31, N 54.54, found: C 23.29, H 1.36, N 54.38.
752, 610, 460 cm-1; elemental analysis calcd (%) for C3H5N5O5 General procedures for the preparation of energetic salts 8a-c.
(191.10): C 18.86, H 2.64, N 36.65; found: C 18.63, H 2.71, N 5-(l,2,4-Oxadiazolyl-3-yl)-1-hydroxytetrazole (0.5 g, 2 mmol)
36.48.
was diluted in EtOH (5 mL) and aqueous ammonia (28 wt% in
water), hydrazine hydrate (80 wt% in water) or hydroxylamine
Hydrazinium 3-dinitromethyl-1,2,4-oxadizole(6b).
1
6b (0.293 g, 71%) as yellow solid. H NMR (600 MHz, DMSO- (50 wt% in water) (2.1 mmol) was added. After stirring at
d6): δH = 7.06 (5Н, s), 9.54 (1Н, s) ppm; 13C NMR (151 MHz, ambient temperature for 2 h, the precipitate was filtered off
DMSO-d6): δC =122.65, 162.56, 167.20 ppm; IR (KBr): ν = 3245, and washed with EtOH and Et2O.
3129, 3031, 2977, 2580, 1552, 1522, 1498, 1472, 1374, 1367, Ammonium 5-(l,2,4-Oxadiazolyl-3-yl)-1-hydroxytetrazole(8a).
1348, 1296, 1270, 1256, 1184, 1152, 11.3, 1085, 958, 898, 883, 8a (0.229 g, 67%) as white solid. 1H NMR (600 MHz, DMSO-d6):
817, 752, 610 cm-1; elemental analysis calcd (%) for C3H6N6O5 δH = 7.33 (4Н, s), 9.75 (1Н, s) ppm; 13C NMR (151 MHz, DMSO-
(206.12): C 17.48, H 2.93, N 40.77; found: C 17.25, H 3.03, N d6): δC = 134.56, 158.46, 167.49 ppm; IR (KBr): ν = 3204, 3197,
40.48.
3117, 3041, 3033, 2852, 1733, 1688, 1601, 1524, 1455, 1435,
1384, 1341, 1288, 1232, 1175, 1107, 1093, 1012, 973, 961, 945,
Hydroxylammonium 3-dinitromethyl-1,2,4-oxadizole(6c).
6c (0.286 g, 69%) as light yellow solid. H NMR (600 MHz, 901, 755, 713, 693, 613, 584, 411 cm-1; elemental analysis
DMSO-d6): δH = 7.04 (3Н, s), 9.57 (1Н, s) ppm; 13C NMR (151 calcd (%) for C3H5N7O2 (171.12): C 21.06, H 2.95, N 57.30,
MHz, DMSO-d6): δC = 122.65, 162.57, 167.21 ppm; IR (KBr): ν = found: C 20.95, H 2.96, N 57.26.
1
3202, 3130, 1552, 1522, 1471, 1426, 1407, 1395, 1366, 1347, Hydrazinium
5-(l,2,4-Oxadiazolyl-3-yl)-1-
1920, 1271, 1185, 1151, 1103, 1086, 958, 897, 884, 817, 752, hydroxytetrazole(8b). 8b (0.287 g, 77%) as white solid. 1H
This journal is © The Royal Society of Chemistry 20xx
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7
a) Y. Zhang, Y. Huang, D. A. Parrish and J. M. Shreeve, J.
NMR (600 MHz, DMSO-d6): δH = 8.28 (5Н, s), 9.67 (1Н, s) ppm;
13C NMR (151 MHz, DMSO-d6): δC = 134.49, 158.51, 167.48
ppm; IR (KBr): ν = 3321, 3201, 3076, 3025, 2841, 2715, 2625,
1650, 1619, 1584, 1524, 1438, 1409, 1305, 1277, 1235, 1186,
1136, 1105, 1073, 975, 893, 757, 710, 690, 614, 589 cm-1;
elemental analysis calcd (%) for C3H6N8O2 (186.14): C 19.36,
H 3.25, N 60.20, found: C 19.28, H 3.27, N 60.12.
View Article Online
Mater. Chem., 2011, 21, 6891; b) Y. Zhang, D. A. Parrish and
DOI: 10.1039/C7DT03320F
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Roussel, H. Graindorge, Angewandte Chemie, 2010, 49, 3177;
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2012, 22, 12659; e) D. Kumar, G. H. Imler, D. A. Parrish and J.
M. Shreeve, J. Mater. Chem. A, 2017.
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Pyrotech., 2012, 37, 536; b) H. Gao, C. Ye, O. D. Gupta, J.-C.
Xiao, M. A. Hiskey, B. Twamley and J. M. Shreeve, Chem. Eur.
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M. Melnikova and N. S. Aleksandrova, Russ.Chem.Bull.,
Int.Ed., 2002, 51, 1533; b) M. A. Epishina, A. S. Kulikov and N.
N. Makhova, Russ.Chem.Bull., Int.Ed., 2008, 57, 644; c) D.
Fischer, T. M. Klapötke, M. Reymann and J. Stierstorfer,
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8
9
Hydroxylammonium 5-(l,2,4-Oxadiazolyl-3-yl)-1-hydroxytetr-
1
azole(8c). 8c ( 0.273 g, 73%) as gray-white solid. H NMR (600
MHz, DMSO-d6): δH = 7.76 (3Н, s), 9.68 (1Н, s) ppm; 13C NMR
(151 MHz, DMSO-d6): δC = 134.76, 158.35, 167.61 ppm; IR
(KBr): ν = 3557, 3240, 3035, 2929, 2706, 1606, 1586, 1548,
1527, 1445, 1416, 1387, 1338, 1275, 1241, 1191, 1171, 1112,
1099, 1036, 1014, 899, 759, 714, 617, 411 cm-1; 13C NMR (151
MHz, D2O): δC = 135.64, 156.64, 167.18 ppm, elemental
analysis calcd (%) for C3H5N7O(187.12): C 19.26, H 2.69, N
52.40, found: C 19.18, H 2.75, N 52.31.
Adv., 2015, 5 ,47248; f) C. He and J. M. Shreeve, Angew.
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Acknowledgements
5
,
This work was supported by the National Natural Science
Foundation of China (No.U1530262, 21376121, 21676147, and
21702196), and the Development Foundation of CAEP (No.
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8 | J. Name., 2012, 00, 1-3
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View Article Online
DOI: 10.1039/C7DT03320F
Exploiting the Energetic Potential of 1,2,4-Oxadiazole Derivatives:
Combining the Benefits of 1,2,4-Oxadiazole Framework with Various
Energetic Functionalities
Chao Yan, Kangcai Wang, Tianlin Liu, Hongwei Yang, Guangbin Cheng*, and Qinghua Zhang*
A series of energetic compounds based on 1,2,4-oxadiazole framework with various
functionalities was synthesized and structurally characterized. Among them, the hydrazinium salt
8b and hydroxylamonium salt 8c exhibited satisfactory calculated detonation performances, while
compound 9 was a potential candidate for the applications of melt-cast explosives.