Potassium 4,5-Bis(dinitromethyl)furoxanate: A Green Primary Explosive with a Positive Oxygen Balance

Article abstract of DOI:10.1002/anie.201509209

Potassium 4,5-bis(dinitromethyl)furoxanate was synthesized readily from cyanoacetic acid. It was characterized by IR spectroscopy, elemental analysis, NMR spectroscopy, and differential scanning calorimetry (DSC), and the structure was confirmed by X-ray single-crystal diffraction. Its positive oxygen balance, high density (2.130 g cm^-3), sensitivity (IS=2 J, FS=5 N), and calculated heat of formation (-421.0 kJ mol^-1), combined with its calculated superior detonation performance (D=7759.0 m s^-1, P=27.3 GPa), make it a competitive replacement as a green primary explosive.

Full text of DOI:10.1002/anie.201509209

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201509209
German Edition: DOI: 10.1002/ange.201509209
Energetic Materials
Potassium 4,5-Bis(dinitromethyl)furoxanate: A Green Primary
Explosive with a Positive Oxygen Balance
Chunlin He and Jeanꢀne M. Shreeve*
In memory of Malcolm MacKenzie Renfrew
Abstract: Potassium 4,5-bis(dinitromethyl)furoxanate was
synthesized readily from cyanoacetic acid. It was characterized
by IR spectroscopy, elemental analysis, NMR spectroscopy,
and differential scanning calorimetry (DSC), and the structure
was confirmed by X-ray single-crystal diffraction. Its positive
The introduction of nitro groups is an efficient way to
improve the OB of compounds. Molecules that contain
dinitromethyl groups show enhanced oxygen balance and
density, which in turn improve their detonation performance
(pressure and velocity). Furthermore, the planarity of the
dinitromethyl group makes those molecules more stable than
trinitromethyl-containing molecules, which have a non-copla-
nar geometric structure. Dinitromethyl-containing azole-
based energetic compounds have been studied extensively
À3
oxygen balance, high density (2.130 gcm ), sensitivity (IS =
2
J, FS = 5 N), and calculated heat of formation
À1
(À421.0 kJmol ), combined with its calculated superior
À1
detonation performance (D = 7759.0 ms , P = 27.3 GPa),
make it a competitive replacement as a green primary
explosive.
[
5]
in the past few years. A general strategy for the synthesis of
dinitromethyl azoles involves the nitration of C-azolylacetic
P
rimary explosives as a class of energetic
compounds show high sensitivity toward
impact, friction, shock, heat, and electro-
static discharge. They are able to transition
from combustion (or deflagration) to det-
onation (fast deflagration to detonation
transition, DDT) and therefore are useful
[
1]
as initiators. Lead-based primary explo-
sives, such as lead azide and lead styphnate,
are still the most commonly used materials
in civilian and military operations. The
toxicity associated with these widely used
lead-based primary explosives is a source
of serious environmental and health-
related problems. Therefore, the develop-
Figure 1. Green candidates for the replacement of lead-based primary explosives.
ment of lead-free, environmentally friendly alternatives to
acid esters with a mixture of concentrated sulfuric acid and
100% nitric acid. This transformation is followed by decar-
boxylation with a base and subsequent acidification. How-
ever, this method has the disadvantage of a rather small
number of known C-azolylacetic acid esters. An alternative
method is the nitration of the more accessible chloroximes by
N O , followed by treatment with potassium iodide and an
[
2]
current primary explosives is a major current focus.
Potassium is an environmentally friendly species with
[
3]
good coordinating ability to energetic ligands. Energetic
potassium salts are considered to be “green” candidates for
the replacement of lead-based primary explosives. To date,
several promising replacements for lead-based primary
2
5
[3,4]
[3,5g]
explosives have been synthesized (Figure 1).
Energetic
acid.
Furoxan as a “hidden” nitro group possesses the
materials with a zero or positive oxygen balance (OB) convert
all carbon into carbon dioxide and all hydrogen into water.
The liberation of minimum amounts of toxic gases is
desirable, so they can be seen as “greener” than compounds
with a negative OB. However, most reported candidates as
green primary explosives have a negative OB (Figure 1).
highest oxygen content (37.2%) among the N-heterocyclic
rings. The combination of the dinitromethyl group with
a furoxan ring dramatically improves the oxygen balance. In
our continuing efforts in seek of high-energy-density materi-
als (HEDMs), we have now synthesized and characterized
a new primary explosive, potassium 4,5-bis(dinitromethyl)-
furoxanate, which exhibits a positive oxygen balance and
properties competitive with those of lead azide.
[
*] Dr. C. He, Prof. Dr. J. M. Shreeve
Department of Chemistry, University of Idaho
Moscow, ID 83844-2343 (USA)
Potassium 4,5-bis(dinitromethyl)furoxanate (5) was
obtained in five steps from cyanoacetic acid (Scheme 1).
Compounds 1–3 were prepared according to the previously
E-mail: jshreeve@uidaho.edu
[
6]
described methods. The nitration of 3 was realized with
Supporting information for this article ia available on the WWW
under http://dx.doi.org/10.1002/anie.201509209.
a mixture of trifluoroacetic acid anhydride (TFAA) and
7
72
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The physical properties of 5 are summar-
ized in Table 2. It possesses a positive oxygen
À3
balance, a measured density of 2.130 gcm at
room temperature, an impact sensitivity (IS)
of 2 J, and a friction sensitivity (FS) of 5 N.
These properties are comparable to those of
lead azide. The heat of formation of 5 was
À1
calculated to be À421.0 kJmol by the use
of the Gaussian03 (Revision D.01) suite of
programs at the level of theory of MP2/6-
3
11++G**//B3LYP/6-31+G** through Born–
Scheme 1. Synthesis of 5.
Haber energy cycles (see Tables S4 and S5 in
the Supporting Information).
[7–9]
The detona-
1
00% HNO . The reaction process was monitored by TLC
3
(
ethyl acetate/hexane 1:9). Compound 4 is a colorless oil
which slowly decomposes upon standing. Therefore, 4 was
treated immediately with KI in methanol, which led to the
precipitation of the light-yellow solid 5. Compound 5 was
insensitive to light and very stable upon storage under
ambient conditions. It was not soluble in methanol or ethanol,
but did dissolve in water, dimethyl sulfoxide (DMSO), and
dimethylformamide (DMF). It started to decompose at 2188C
without melting.
1
3
The structure of 5 was confirmed by IR and C NMR
15
spectroscopy, elemental analysis, N NMR spectroscopy, and
X-ray diffraction. Four nitrogen signals were observed in the
1
5
N NMR spectrum. They were assigned based on GIAO
[7]
NMR calculation with Gaussian03 (Figure 2). Crystals of 5
were grown in water as yellow prisms, and the single-crystal
X-ray structure of 5 was determined at 100 K (Figure 3).
Figure 3. Crystal structure of 5 (ellipsoids are set at 50% probability).
tion properties were calculated by using EXPLO5 (ver-
[
10]
sion6.01) code.
(
The superior detonation properties of 5
À1
D = 7759.0 ms , P = 27.3 GPa) as compared to those of lead
azide, and the small amount of toxic materials (CO% +
NO% = 0.29%) in the detonation products, make it promis-
ing as a green primary explosive (Figure 4; see Table S6 for
the composition of the major detonation products).
1
5
Figure 2. N NMR spectrum of compound 5.
Compound 5 crystallizes in the monoclinic space group P2 /c,
1
with four molecules per unit cell (Table 1). The carbon atoms
C3, C4 and all the atoms in the furoxan ring are coplanar, with
two of the four nitro groups located on each side of the
furoxan plane. The two dinitromethane moieties are almost
planar, with O7 and O4 showing the biggest deviation of
Figure 4. Composition of gas-phase detonation products for 5 [wt%].
0
.1897 and 0.2811 Š from the [N5, C4, N6] plane and the [N3,
C3, N4] plane, respectively. Those two planes form dihedral
angles of 57.193 and 55.0768 with the furoxan plane. (More
details about the crystal structure can be found in the
Supporting Information.)
In summary, potassium 4,5-bis(dinitromethyl)furoxanate
was obtained in five steps from commercially available
cyanoacetic acid through the use of a more accessible
nitration method with a mixture of trifluoroacetic acid
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Table 1: Crystal data and structure refinement for 5.
as the green detonation products make it a competitive
candidate as a green primary explosive.
Empirical formula
C K N O
4 2 6 10
Formula weight
Temperature [K]
Crystal system
Space group
a [Š]
b [Š]
c [Š]
a [8]
b [8]
370.30
100
monoclinic
Experimental Section
Caution: All furoxan compounds are potential energetic materials
and may explode under certain conditions. Appropriate safety
precautions should be taken when preparing and handling.
The detailed experimental description of the entire synthetic
procedure is shown in Scheme 1; compounds 1–3 were prepared
P2 /c
1
12.3388(4)
7.3181(2)
12.6248(4)
90
96.2370(10)
90
1133.23(6)
4
2.170
[
6]
according to previously reported methods.
Compound 3 (2.41 g, 10 mmol) in CHCl3 (20 mL) was added
dropwise to a stirred mixture of trifluoroacetic acid anhydride
g [8]
Volume [Š ]
3
(14 mL) and 100% HNO3 (8 mL), while maintaining the reaction
Z
À3
temperature between À5 and 08C. After the addition was complete,
the ice bath was removed, and the mixture was allowed to warm
slowly to room temperature. It was stirred for another 2 h, and then
1calcd [gcm
m [mm
F(000)
]
À1
]
0.914
736.0
0.2”0.15”0.15
3
poured into ice water (50 mL) and extracted with CHCl (3 ” 20 mL).
3
Crystal size [mm ]
Radiation
The organic phases were combined, washed with water and brine,
dried over sodium sulfate, and then concentrated under vacuum to
provide the intermediate 4 as a colorless oil. Compound 4 was
dissolved in methanol (20 mL), potassium iodide (4 g, 24 mmol) in
methanol (30 mL) was added dropwise, and the mixture was stirred
overnight at room temperature. The precipitate formed was collected
by filtration and washed with cold water (5 mL) and then methanol
(5 mL) and ethyl ether (10 mL) to give 5 (1.12 g, 30.2%) as a light-
MoK (l=0.71073)
a
2q range for data collection [8] 6.444–61.144
Index ranges
À17ꢀhꢀ17, À10ꢀkꢀ10,
À18ꢀlꢀ18
Reflections collected
Independent reflections
Data/restraints/parameters
41608
3483 [Rint =0.0357, Rsigma =0.0165]
3483/0/199
1.065
2
Goodness-of-fit on F
À1
yellow solid. Tdec (58Cmin ): 218.38C; IR (KBr): 1616, 1533, 1511,
Final R indexes [Iꢁ2s(I)]
R =0.0237, wR =0.0556
1
2
1
485, 1464, 1398, 1282, 1233, 1190, 1151, 1138, 991, 964, 830, 779,
Final R indexes (all data)
R =0.0301, wR =0.0583
1
2
À1
13
1
À3
749 cm
1
;
C{ H} NMR ([D ]DMSO): 112.05, 120.60, 123.23,
6
Largest diff. peak/hole [eŠ
CCDC number
]
0.51/À0.22
1
5
1
52.09 ppm; N{ H} NMR ([D ]DMSO): À5.84, À23.30, À24.35,
6
1428290
À31.66 ppm; elemental analysis (C K N O , 370.27): calcd: C 12.97,
4
2
6
10
N 22.70; found: C 13.11, N: 22.20.
Table 2: Physical properties of lead azide and compound 5.
Acknowledgements
Pb(N3)2
5
Formula
N Pb
C K N O
10
6
4
2
6
This research was supported by the Office of Naval Research
(N00014-12-1-0536) and the Defense Threat Reduction
Agency (HDTRA 1-11-1-0034). We are indebted to Dr.
Orion Berryman for crystal structures (NSF—CHE1337908
and CoBRE NIGMS P20M103546).
À1
M [gmol
]
291.3
315.0
À11.0
À11.0
28.9
370.3
218.3
21.3
4.3
22.7
65.9
2.130
2
[
a]
Tdec [8C]
[
b]
WCO [%]
[
c]
WCO2 [%]
[
d]
N [%]
N+O [%]
[
e]
28.9
À3 [f]
1
[gcm
]
4.800
2.5–4.0
0.1–1
450.1
3353
Keywords: energetic materials · furoxans · heterocycles ·
oxygen balance · primary explosives
[
g]
IS [J]
[
h]
FS [N]
DH [kJmol
5
À1 [i]
]
À421.0
f
[
j]
How to cite: Angew. Chem. Int. Ed. 2016, 55, 772–775
Angew. Chem. 2016, 128, 782–785
Tdet [K]
D [ms
P [GPa]
3574
À1 [k]
]
5876.8
33.4
7759.0
27.3
[
l]
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Received: October 1, 2015
Published online: November 6, 2015
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