Bis[3-(5-nitroimino-1,2,4-triazolate)]-based energetic salts: Synthesis and promising properties of a new family of high-density insensitive materials

Article abstract of DOI:10.1021/ja1055033

Bis[3-(5-nitroimino-1,2,4-triazolate)]-based energetic salts were synthesized in a simple, straightforward manner. They exhibit low solubility in available solvents, high hydrolytic stability, excellent thermal stability, high density, positive heat of formation, low shock sensitivity, and excellent detonation properties. The physical and energetic properties of some salts are similar and even superior to those of RDX.

Full text of DOI:10.1021/ja1055033

Published on Web 08/06/2010
Bis[3-(5-nitroimino-1,2,4-triazolate)]-Based Energetic Salts: Synthesis and
Promising Properties of a New Family of High-Density Insensitive Materials
,†
†
‡
†
,‡
Ruihu Wang,* Hongyan Xu, Yong Guo, Rongjian Sa, and Jean’ne M. Shreeve*
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese
Academy of Sciences, Fuzhou, Fujian 350002, China, and Department of Chemistry, UniVersity of Idaho,
Moscow, Idaho 83844-2343
Received June 23, 2010; E-mail: ruihu@fjirsm ac.cn; jshreeve@uidaho.edu
expensive, and the overall yield is quite low. Two of the key
requirements for practical application of an energetic compound are
that its synthesis must be simple and the starting materials should be
Abstract: Bis[3-(5-nitroimino-1,2,4-triazolate)]-based energetic
salts were synthesized in a simple, straightforward manner. They
exhibit low solubility in available solvents, high hydrolytic stability,
excellent thermal stability, high density, positive heat of formation,
low shock sensitivity, and excellent detonation properties. The
physical and energetic properties of some salts are similar and
even superior to those of RDX.
inexpensive. On the basis of the symmetric nature of H
easier and more straightforward method for its synthesis was developed
Scheme 1). The condensation of inexpensive oxalic acid with
2
BNT, a much
(
aminoguanidine hydrochloride and subsequent cyclization gave rise
10
to bis[3-(5-amino-1,2,4-triazolyl)], and subsequent nitration with
concentrated nitric acid and sulfuric acid afforded H
2) was obtained by adding aqueous NaOH to a hot aqueous solution
of H BNT is soluble in hot water. The metathesis
BNT (pH ∼10). Na
reactions of Na BNT with monocationic halides in hot water resulted
in the formation of corresponding energetic salts 3-11. Interestingly,
the treatment of Na BNT with excesses of dicationic sulfates gave
2 2
BNT. Na BNT
(
Energetic materials are extensively used for a variety of military
purposes and industrial applications. Current interest has been focused
on the development of high-energy-density materials (HEDMs) with
higher performance and/or decreased sensitivity to thermal shock and
2
2
2
2
1
friction. However, the requirements of insensitivity and high energy
rise to 12 and 13 in high yields and purities.
are quite often contradictory to each other, making the development
of new HEDMs a difficult and challenging problem. In the pursuit of
new energetic materials, high-nitrogen heterocyclic compounds have
Scheme 1
2
-4
attracted considerable attention.
Along with the development of
3
ionic liquids and their applications in energetic fields, nitrogen-
containing heterocyclic halide-free energetic salts have gradually
become a hot topic, as these salts possess intrinsically low volatility,
high thermal stability, a simple synthesis process, and readily modified
3-6
properties.
and synthesis of HEDMs for specific purposes.
The N-NO group is an important “explosophore” that is present
in many energetic compounds. When the R-NH-NO group is
5c,7
This provides a powerful methodology for the design
2
2
4
b,6b
bonded to tetrazole
or at the 3(5)-position of 1,2,4-triazole,
it is usually assigned as a nitroimine structure. The strong electron-
withdrawing effect of the nitro group can deprotonate azoles to
form energetic salts when paired with bases. However, it is not
clear which structure is preferable in primary nitroamines and
nitroimines when NH-NO is bonded to azoles.
2
In our continuing effort to seek more powerful, less sensitive, eco-
As shown in Table 1, all of the salts exhibit excellent thermal
stability, which most likely can be attributed to the extensive and
strong hydrogen-bonding interactions between cations and anions.
The decomposition temperatures, which fall in the range 198-290
friendly explosives and propellants, we were interested in bis[3-(5-
nitroimino-1,2,4-triazole)] (H
2
BNT) because its monoanionic salt
°
C, are higher than that of H
those of RDX (230 °C) and HMX (287 °C).
The densities of 3-13, which are in the range 1.63-1.95 g/cm ,
2
BNT (165 °C) and comparable to
-
(HBNT ) showed promising thermal stability (>200 °C) and poor
8
solubility in organic solvents, water, and acids. The structure of
BNT was (without proof) considered to be bis(3-nitroimine-1,2,4-
triazole), which is different from the nitroamine-bonded 1,2,4-triazole
3
H
2
are higher than those of the reported 3-nitroamino-1,2,4-triazole
5c,7
analogues. It should be noted that the densities of commonly used
5c,7
analogues.
energetic performance and applications, it was significant to unambigu-
ously determine the structure of H BNT. Recently, the sensitivity of
BNT to thermal and mechanical initiation was reported. Herein, we
Since the structure is a key point for exploration of
explosives such as TNT, TATB, RDX, and HMX are in this range.
Interestingly, the densities of 3 and 12 fall in the range for new high-
2
3
performance energetic materials (1.8-2.0 g/cm ). Their high densities
9
H
2
are ascribed to the extensive and strong hydrogen bonds between
report the synthesis and characterization of BNT-based dianionic salts.
Although HBNT and its monoanionic salts have been reported,
2-
cations and BNT . To the best of our knowledge, the density of 12
-
8
3
(
1.95 g/cm ) is the highest of the reported energetic salts.
their synthetic procedures are tedious; also, the starting materials are
Salts 5-13 possess much lower impact sensitivities than RDX and
HMX (7.4 J), which suggests that they can serve as promising
candidates for safer materials to replace RDX. The impact sensitivities
†
Fujian Institute of Research on the Structure of Matter.
University of Idaho.
‡
1
1904 9 J. AM. CHEM. SOC. 2010, 132, 11904–11905
10.1021/ja1055033  2010 American Chemical Society

C O M M U N I C A T I O N S
Table 1. Properties of Dianionic Energetic Salts
a
b
3
c
d
OB
e
f
g
h
h
i
j
k
compd
T
m
(°C)
T
d
(°C)
d
meas (g/cm )
IS (J)
∆
f
Hcation (kJ/mol)
∆
f
Hlat (kJ/mol)
∆
f
Hsalt (kJ/mol)
∆
f
Hsalt (kJ/g)
P (GPa)
v
D
(m/s)
Isp (s)
l
3
dec
217
218
220
265
248
235
244
198
281
222
290
295
1.83 (1.89) -49.6
-
-
626.4
669.5
770.0
575.9
667.4
769
1392.8
1309.3
1269.4
1234.5
1183.1
1143.4
1104.1
1121.1
1019.4
1963.2
1829.6
-
105.8
275.5
516.4
163.1
397.5
640.4
884.7
808.7
837.0
47.2
319.8
-67.0
-154.2
92.6
0.36
0.86
1.61
0.44
0.98
1.47
1.91
1.67
1.34
0.14
0.71
34.9
32.4
26.2
26.6
26.3
27.0
27.0
28.3
27.3
36.0
24.3
19.5
31.2
35.2
39.6
9407
8856
8455
8634
8603
8701
8705
8792
8474
9399
8267
6881
8114
8977
9320
200.8
240.0
227.1
191.3
202.3
212.6
221.9
207.8
212.3
194.7
182.8
-
4
5
6
7
8
9
1
1
1
1
dec
dec
dec
242
dec
237
178
dec
162
dec
81
1.78
1.63
-34.8
-50.0
11
l
1.70 (1.77) -64.1 >40
1.71
1.68
1.64
-63.3 >40
-62.6
-62.0
31
23
871.5
842
l
0
1
2
3
1.75 (1.78) -66.1 >40
1.80
1.95
1.80
1.65
1.93
1.82
1.91
-63.9 >40
805.3
1764.6
1903.6
-
-46.2
-63.7
-74.0
-55.8
-21.6
-21.6
38
32
15
50
7.4
7.4
TNT
-0.30
-0.54
0.42
TATB
RDX
HMX
350
dec
dec
∼360
-
-
-
230
-
-
-
-
-
287
-
104.8
0.35
a
b
c
Melting point. Thermal degradation temperature. Measured density. Values in parentheses were corrected by subtracting the volume of a water
3
d
e
f
g
molecule [V(H O) ) 25 Å ]. Oxygen balance. Impact sensitivity. Calculated molar heat of formation of the cation. Calculated molar lattice energy.
Calculated heat of formation of the salt. Calculated detonation pressure. Calculated detonation velocity. Calculated specific impulse in seconds.
Calculations were performed using the corrected density.
2
h
i
j
k
l
of 6, 7, 10, and 11 are greater than 40 J, so they can be classified as
salts fall in the range for new high-performance energetic materials
11
3
insensitive materials.
(1.8-2.0 g/cm ). One dicationic salt possesses the highest density of
The calculated heat of formation of BNT2- (245.8 kJ/mol) is much
more positive than that of monoanionic 3-nitroimino-1,2,4-triazolate
the reported energetic salts (1.95 g/cm ). The calculated detonation
3
velocities and detonation pressures of the salts are higher than those
of conventionally used TNT and TATB. Interestingly, the properties
of ammonium, hydroxyammonium, and carbonic dihydrazidinium salts
are similar and even superior to that of RDX, which suggests that
they may serve as a series of promising alternatives to RDX.
5c
(
-13.5 kJ/mol). Thus, it is not surprising that 6 and 7 exhibit much
higher heats of formation than their monoanionic guanidinium (0.27
5c
kJ/g) and aminoguanidinium (0.78 kJ/g) analogues. All of the salts
possess positive heats of formation that fall in the range 0.14-1.91
kJ/g. As anticipated, the calculated heats of formation increase with
increasing nitrogen content in the guanidinium-derivatized salts 6-9.
The calculated detonation pressures of 3-13, which lie in the range
Acknowledgment. The authors gratefully acknowledge the
support of DTRA (HDTRA1-07-1-0024), NSF (CHE-0315275),
ONR (N00014-10-1-0097), and NSFC (20971122), “One Hundred
Talent Project” in Chinese Academy of Sciences.
2
4.3-36.0 GPa, are higher than that of TNT (19.53 GPa) and
comparable to those of TATB (31.15 GPa) and RDX (35.2 GPa).
Detonation velocities (V ) were found in to be the range 8267-9407
D
Supporting Information Available: Experimental details for the
syntheses and characterization of all compounds; descriptions, figures, and
a CIF file of the crystal structure; details of the calculations; and description
m/s; they are higher than those of TNT (6881 m/s) and TATB (8114
m/s) and comparable to those of RDX (8977 m/s) and HMX (9320
m/s). All of the salts have specific impulse values ranging between
2
of and figure showing the charge distributions of H BNT. This material is
1
82.8 and 240.0 s. The promising performance suggests potential
available free of charge via the Internet at http://pubs.acs.org.
2-
applications of BNT salts as ingredients in explosives and propellants.
This is especially the case for 3, 4, and 12, as their energetic
performance values are very similar and even superior to those of RDX.
Single-crystal X-ray diffraction analysis confirmed the structure
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2
(
1
2
hydrogen bonds with the nearest nitroimine oxygen atoms. The
hydrogen bonds were kept in model 1, and the binding energy of model
1
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In summary, a simple and straightforward approach for the synthesis
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2
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(
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2
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(
(
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JA1055033
J. AM. CHEM. SOC. 9 VOL. 132, NO. 34, 2010 11905