Synthesis, Characterization and Properties of Ureido-Furazan Derivatives

Article abstract of DOI:10.1002/jhet.3109

The reaction of a variety of amino-furazans with chlorosulfonyl isocyanate was carried out to synthesize ureido-furazans. The nitration to nitro-ureido-furazan was successful in the case of 3-nitro-4-nitroureido-furazan and 3,4-dinitroureido-furazan. Furthermore, furazan derivatives linked to a second amino-oxadiazole were synthesized. All compounds were intensively characterized by X-ray diffraction measurements, NMR spectroscopy, vibrational spectroscopy (IR, Raman), BAM sensitivity tests and differential thermal analysis. The energetic properties were calculated using Explo5 6.03.

Full text of DOI:10.1002/jhet.3109

Month 2018
Synthesis, Characterization and Properties of Ureido-Furazan Derivatives
Tobias S. Hermann, Thomas M. Klapötke,* Burkhard Krumm,
and Jörg Stierstorfer
Department of Chemistry, Ludwig-Maximilian University Munich, Butenandtstr. 5-13(D), 81377 Munich, Germany
*
E-mail: tmk@cup.uni-muenchen.de
Received October 5, 2017
DOI 10.1002/jhet.3109
Published online 00 Month 2018 in Wiley Online Library (wileyonlinelibrary.com).
Dedicated to Professor Peter Politzer on the occasion of his 80th birthday.
The reaction of a variety of amino-furazans with chlorosulfonyl isocyanate was carried out to synthe-
size ureido-furazans. The nitration to nitro-ureido-furazan was successful in the case of 3-nitro-4-
nitroureido-furazan and 3,4-dinitroureido-furazan. Furthermore, furazan derivatives linked to a second
amino-oxadiazole were synthesized. All compounds were intensively characterized by X-ray diffraction
measurements, NMR spectroscopy, vibrational spectroscopy (IR, Raman), BAM sensitivity tests and dif-
ferential thermal analysis. The energetic properties were calculated using EXPLO5 6.03.
J. Heterocyclic Chem., 00, 00 (2018).
INTRODUCTION
derivatives are also used as alternatives for carbonyl
containing compounds, such as carbamates, amides,
esters, and hydroxamic esters [13,14].
Research towards new high-energy dense materials
HEDM) is still required for future applications in
(
In the past decades, the furazan group has thoroughly
been investigated, and it was proven that the furazan ring
and its energetic properties are perfect building blocks for
energetic materials [15–18]. Amino furazans are not only
known for their high heat of formation but also their
thermal and chemical stability. Selected furazans such as
potassium 4,5-bis(dinitromethyl)furoxanate have been
described as green replacements for lead-based primary
explosives, which require a high sensitivity toward
impact, friction and electrostatic discharge [16]. In terms
of synthesizing oxygen-rich compounds (solid state
oxidizers), furazans are useful backbones because of their
ring oxygen atom. Oxidizers are compounds with a
positive oxygen balance. The oxygen balance is defined
as oxygen excess during combustion. This excess is used
to oxidize the propellant’s fuel. Oxidizers usually burn
without residues, because all carbon atoms are converted
into carbon monoxide or dioxide, hydrogen atoms into
industrial, military, and civil sectors [1,2]. Particularly,
toxicity and safety problems that need to be solved to
meet current regulations, for example, REACH [3]. These
new energetic materials must also be equal or better in
performance compared with their traditional predecessors.
Many nitrogen and oxygen containing heterocyclic
compounds have been shown to exhibit good energetic
properties because of high densities and high positive
heat of formations [4]. Particularly, triazoles and
oxadiazoles have been intensively investigated thus far
[
5–10]. They differ only by the replacement of a nitrogen
atom with an oxygen atom. Different regioisomeric
oxadiazole derivatives are depicted in Scheme 1. The
great interest in these oxadiazoles can also be seen in the
amount of patents in the last decade [11]. The main use
of oxadiazoles in the industrial sector is for medical
devices, pesticides, or polymers [12]. Oxadiazole
©
2018 Wiley Periodicals, Inc.

T. S. Hermann, T. M. Klapötke, B. Krumm, and J. Stierstorfer
Vol 000
Scheme 1. Structures of oxadiazole derivatives: (a) 1,2,5-oxadiazole
furazan), (b) 1,2,4-oxadiazole, (c) 1,2,3-oxadiazole, and (d) 1,3,4-oxadiazole.
(Scheme 2), which further could be nitrated to a nitro
ureido derivative. The CSI reaction conditions and
mechanisms have been investigated in our research group
to synthesize carbamates from alcohols [32,33].
(
Similar to literature known reactions using CSI, the
yields of ureido derivatives reported in this investigation
were about 90%. In order to synthesize more energetic
compounds, attempts were carried out to nitrate the
ureido moieties. In this investigation, different acids
water, and nitrogen into dinitrogen [19]. Through the
introduction of nitro groups, the oxygen balance can be
further tuned to positive values. In order to synthesize
energetic compounds with outstanding performance, N–
(
fuming HNO , mixed acid, and Ac O/HNO ) and
3 2 3
nonacidic conditions such as N O were employed. The
2
5
NO groups play an important role. This functional group
2
nitration was successful for 3-nitro-4-nitroureido-furazan
improves the oxygen and nitrogen balance and also
yields to an improvement of the high heat of formation
and density [20,21]. Nitro ureido compounds are known
to have good explosive performances and high densities
(
3
2) and 3,4-dinitroureido-furazan (4). In the case of
0 0 0 0
,3 -diureido-4,4 -azoxyfurazan (5), 3,3 -diureido-4,4 -
0
0
azofurazan (6), and 3,3 -diureido-4,4 -bifurazan (7),
the nitration in acidic and nonacidic conditions led to
the amines, under loss of the CO–NH2 moiety. The
corresponding nitramine compounds have already been
characterized by our research group [15]. Upon heating
of 2 in ethanol for the purpose of recrystallization, a
replacement of the nitramino moiety to 3-nitro-4-
ethoxycarbamoyl furazan (8) occurred.
[22]. In order to combine the benefits of oxadiazoles and
nitro ureido, new energetic compounds were synthesized
and described herein. According to our literature
research, only carbon chains, phenyl, and nitrated phenyl
nitro ureidos were synthesized so far [23–25]. Ureido-
furazanes have not been synthesized so far. To the best of
our knowledge, in this paper, the first ureido 1,2,5-
oxadiazolyl derivatives are described.
Furthermore, two different attempts to synthesize more
complex ureido derivatives with two different oxadiazols
were investigated (Scheme 3). The reaction of 4-amino-3-
amino(hydroxyimino)methyl-furoxan [34] with cyanogen
bromide in aqueous conditions led to 4-amino-3-(5-
amino-1,2,4-oxadiazolyl) furoxan (9). In order to increase
the energetic properties, further oxidation in
peroxymonosulfuric acid (Caro’s acid) yielded 4-nitro-
3-(5-amino-1,2,4-oxadiazolyl) furoxan (10). Similar to
the synthesis of 9, 3,4-bis-amino(hydroxyimino)methyl
furoxane [35] was reacted with cyanogen bromide to 3,4-
bis-(5-amino-1,2,4-oxadiazolyl) furoxan (11). Further
reactions of 9, 10, and 11 with CSI were unsuccessful.
This result leads to the assumption that the reactivity of
RESULTS AND DISCUSSION
Synthesis and characterization.
The synthesis of the
starting materials,
3,4-diaminofurazan, 3-amino-4-
0
0
0
nitrofurazan, 3,3 -diamino-4,4 -azofurazan, 3,3 -diamino-4,
0
0 0
4
-azoxyfurazan, and C–C coupled 3,3 -dinitro-4,4 -
bifurazan, was performed according literature [26–31].
The starting materials were reacted with chlorosulfonyl
isocyanate (CSI) under anhydrous conditions. The
reaction of amines with CSI leads to ureido moieties
Scheme 2. Synthesis of ureido (1, 3, 5, 6, and 7) and nitro ureido furazans (2 and 4).
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2018
Energetic Ureido-Furazans
Scheme 3. Synthesis of amino-1,2,4-oxadiazol furazan derivatives.
the amino group of the 1,2,4-oxadiazoles is not high
enough for the reaction with CSI. Another important
reason for their low reactivity is the very low solubility
of the 1,2,4-oxadiazole derivatives in common organic
solvents.
resonances of 1 and 2 are displayed. The carbonyl
resonance, in the range of 140–150 ppm of the ureido and
nitro ureido moiety, is the most significant resonance in the
13
C NMR spectra. The nitro groups of the nitro ureidos (2
and 4) are observed at around ꢀ40 ppm and additionally
14
Spectroscopy.
The vibrational analysis of 2 and 4
the nitro moiety of 2 at ꢀ33 ppm in the N NMR spectrum.
showed the characteristic antisymmetric ν (NO ) and the
Crystal structures. The structures of 1, 4, 8, and 10 in
the solid state were determined by low temperature X-ray
diffraction.
as
2
symmetric ν (NO ) stretching vibrations in the range of
s
2
ꢀ
1
ꢀ1
1
620–1506 cm and 1385–1251 cm , respectively. The
C–N, C–O, and C–C vibrations of 1–11 are observed in
the typical ranges for heterocycles and CHNO based
aliphatic compounds.
The highest density at 173 K was measured for
ꢀ
3
compound 4 in the triclinic space group P-1 (1.91 g cm
,
Fig. 3) compared with 10 in the monoclinic space group
1
ꢀ3
Comparing the H NMR spectra, a trend for the ureido
P2 /c (1.87 g cm Fig. 5), and the orthorhombic space
1
ꢀ
3
hydrogen atoms can be observed. All NH resonances of
groups, 1 P2 2 2 (1.72 g cm , Fig. 2) and 8 Pbca
2
1 1 1
ꢀ
3
the ureido moieties are found in the range between 7 and
(1.61 g cm , Fig. 4).
5
ppm as broadened signals, because of the ketoꢀenol
The bond lengths and angles are in the range of
literature reported N,O-heterocyclic compounds [15,38].
Selected bond lengths and angles are given in
Figures 2–5. Details on the measurements and
refinements are listed in Table 1.
tautomerism and restricted rotation [36,37]. Due to the
higher acidity of the NHNO2 hydrogen atom, the
resonances of the nitro ureidos are shifted downfield below
1
1
0 ppm. This is shown in Figure 1, where the
H
1
Figure 1. H NMR spectra of 3-nitro-4-ureido-furazan (1) and 3-nitro-4-nitroureido-furazan (2) in DMSO-D
6
. [Color figure can be viewed at
wileyonlinelibrary.com]
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

T. S. Hermann, T. M. Klapötke, B. Krumm, and J. Stierstorfer
Vol 000
Figure 4. Molecular structure of 3-nitro-4-ethyoxycarbamoyl furazan (8).
Selected bond lengths (Å) and angles (deg.): C1–N2 1.460(4), C2–N4
Figure 2. Molecular structure of 3-nitro-4-ureido-furazan (1). Selected
bond lengths (Å) and angles (deg.): C3–N1 1.45(2), C2–N4 1.363(2),
C3–N3 1.328(2). C2–C1–N3 129.04(14), C1–C2–N4 126.93(14), N4–
C3–N5 113.80(14). N1–C1–C2–N4 179.67(14), N2–C2–C1–N3
1
.362(4), O5–C4 454 (4). C2–C1–N1 107.6(3), C1–C2–N4 126.1(3),
C3–O5–C4 117.1 (3). N1–C2–C1–N3 176.9(3), N2–C1–C2–N4
78.7(3), O4–C3–O5–C4 2.8(5). [Color figure can be viewed at
1
0.49(18). [Color figure can be viewed at wileyonlinelibrary.com]
wileyonlinelibrary.com]
Figure 5. Molecular structure of 4-nitro-3-(5-amino-1,2,4-oxadiazolyl)
furoxan (10). Selected bond lengths (Å) and angles (deg.): C2–N3
1
.451(2), N1–O2 1.217(2), N4–O5 1.430(2), C4–N6 1.312(2); N2–C2–
Figure 3. Molecular structure of 3,4-dinitroureido-furazan (4). Selected
bond lengths (Å) and angles (deg.): C1–N3 1.388(2), C2–N6 1.391(2),
C3–N4 1.395(2), C4–N7 1.390(2), N4–N5 1.369(2), N7–N8 1.370(2).
C2–C1–N3 127.47(17), C1–C2–N6 129.81(17). N2–C2–C1–N3
N3 117.8 (1), C2–C1–C3 132.0(1), O5–C4–N6 118.1 (1); O1–N2–C2–
N3 173.9 (1), C2–C1–C3–N5 170.9 (2). [Color figure can be viewed at
wileyonlinelibrary.com]
177.44(17), N1–C1–C2–N6 176.56(18), N6–C4–N7–N8 4.4(3), N3–
C3–N4–N5 3.1(3). [Color figure can be viewed at wileyonlinelibrary.com]
(0.75 and 1.5 J), respectively. The positive oxygen
balances of 2 (+14.7) and 4 (+5.8) causes a residue-
free burning. Additionally, the positive oxygen balance
has a direct influence on the specific impulse. The
specific impulse of 2 was calculated to be 260 s for the
water-free compound. In mixtures with aluminum and
binder, the optimized specific impulse is 244 s. In
comparison, 4 has a specific impulse of 239 s for the
Energetic properties. The calculated physicochemical
and energetic properties of 1–4 are listed in Tables 2
and 3. In terms of energetic properties, the most
interesting compounds are 2 and 4, due to their
functional nitro ureido groups and positive oxygen
balance. The sensitivities were measured with respect to
BAM standards. The sensitivities of compounds 5–11
were determined but not listed in Table 3, because of
their expected complete insensitivity. Compounds 1–4
are not sensitive towards friction (360 N). Furthermore,
compounds 1 and 3 show no sensitivity towards impact
or electrical discharge. Compared with this, 2 and 4
show higher sensitivities towards impact (4 and 7 J)
and moderate sensitivity towards electrical discharge
neat compound and 230
s
for the optimized
formulation. These values are slightly lower than that
(264 s) for the widely used oxidizer ammonium
perchlorate in mixtures.
The nitration of the ureido functional group leads to an
ꢀ
1
ꢀ1
improvement of about 70 kJ mol
1
(63 kJ mol 1,
36 kJ mol 2) according to the calculated enthalpies.
The same trend is observed for compound 4, were the
ꢀ
1
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2018
Energetic Ureido-Furazans
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DOI 10.1002/jhet

T. S. Hermann, T. M. Klapötke, B. Krumm, and J. Stierstorfer
Vol 000
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2018
Energetic Ureido-Furazans
Table 3
Calculated (EXPLO5 6.03) detonation, combustion parameters, and sensitivity data of 1–4.
1
2
3
4
RDX
PETN
ꢀ
ꢀ1
3
a)
k)
k)
density (g cm )b)
1.68
63
41
1.85
1.95
1.87
ꢀ22
ꢀ227
ꢀ4626
322
8685
3405
239
1.80 [38,39]
86
1.75
480
1423
ꢀ5995
316
8525
3959
257
0
Δ
Δ
Δ
f
H (kJ mol
)
136
420
ꢀ162
ꢀ1196
ꢀ2037
245
8283
1767
161
0
ꢀ1 c)
f
U (kJ kg
)
489
ꢀ
1 d)
exU° (kJ kg
)
ꢀ4323
ꢀ5692
ꢀ5743
e)
P
CJ (kbar)
236
348
380
ꢀ
1
f)
VDet (m s
)
7759
3317
225
225
225
8930
4189
260
241
244
8983
4232
258
249
249
g)
Tex (K)
h)
I
s
I
s
I
s
(s)
i)
(s) (15% Al, binder)
(s) (Al, binder)
201
203
229
230
257
251
j)
a
Densities at room temperature.
Enthalpy calculated by the atomization method and CBS-4 M electronic enthalpies from Gaussian 09 [40,41].
b
c
Energy of formation.
d
Heat of detonation.
Detonation pressure.
e
f
Detonation velocity [42].
g
Detonation temperature.
h
i
Specific impulse (EXPLO5 6.03: 70 bar chamber pressure, 10 bar expansion conditions equilibrium expansion).
Specific impulse (15% Al, 6% polybutadiene acrylic acid, 6% polybutadiene acrylonitrile and 2% bisphenyl A ether, EXPLO5 6.03: 70 bar chamber
pressure, 1 bar expansion conditions equilibrium expansion).
j
Optimized specific impulse [Al (%): 1: 15, 2: 11, 3: 17, 4: 13; 6% polybutadiene acrylic acid, 6% polybutadiene acrylonitrile, and 2% bisphenyl A ether).
Density measured by pycnometry.
k
ꢀ
1
increase in enthalpy is twice (2 × 70 kJ mol
(
)
routes to the heterocyclic compounds 1–11 are relatively
easy. IR and NMR spectroscopy are valuable methods for
identification. Two ureido moieties were converted
successfully (2, 4) to the corresponding nitro ureido
derivatives. Comparison of the enthalpy calculations
showed, that nitration of an ureido functional group leads
to an improvement of the enthalpy (~70 kJ mol per
ureido group) but also leads to a decrease in thermal
stability. Except for 2 and 4, all compounds are low
sensitive toward impact and friction and have moderate
thermal stabilities. As expected, the ureidos show higher
thermal stabilities than the corresponding nitro ureido
derivates. Compound 2 is very sensitive toward impact.
The physicochemical and explosive properties of 1–4 make
them potential energetic materials and furthermore
potential precursors for energetic polymers.
ꢀ
1
ꢀ1
ꢀ162 kJ mol 3, ꢀ22 kJ mol 4).
Compounds 2 and 4 also show interesting calculated
detonation values. The values of and are
2
4
comparable with RDX. Comparing the energetic
properties of 2 and 4 with RDX and PETN, the heat
of detonation [ꢀ5692 (2), ꢀ4626 (4) and ꢀ5743
ꢀ
1
ꢀ
1
(
[
RDX), ꢀ5995 kJ kg
(PETN)], detonation pressure
348 (2), 322 (4), and 380 (RDX), 316 kbar (PETN)],
detonation velocity [8930, 8685, and 8983 (RDX), 8525 m
(PETN)] and detonation temperature [4189 (2), 3405
4), and 4232 (RDX), 3959 K (PETN)] are in a similar
ꢀ
1
s
(
range or slightly better. Responsible for the good
detonation values is the nitro ureido moiety and the
energetic furazan backbone. This also is supported by the
high nitrogen and oxygen content, such as for RDX. This
is also displayed by comparing the detonation values of 1
and 3, which are significantly lower.
The mentioned properties of 1–4, make them not only
green explosives, in a sense of being free of heavy
metals, but also useful precursors for potential energetic
polymers, for example, if they would be reacted with
dihalide compounds such as phosgene.
EXPERIMENTAL SECTION
General methods. The low-temperature single-crystal
X-ray diffraction measurements were performed on an
Oxford XCalibur3 diffractometer equipped with
a
Spellman generator (voltage 50 kV, current 40 mA) and a
KappaCCD detector operating with MoKα radiation
(λ = 0.7107 Å). Data collection was performed using the
CRYSALIS CCD software [43]. The data reduction was
carried out using the CRYSALIS RED software [44]. The
solution of the structure was performed by direct methods
(SIR97) [45] and refined by full-matrix least-squares on F2
CONCLUSION
In this article, various heterocyclic ureido derivatives were
synthesized in order to meet current requirements for safer
and more powerful energetic materials. The synthetic
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

T. S. Hermann, T. M. Klapötke, B. Krumm, and J. Stierstorfer
Vol 000
(
[
SHELXL) [46] implemented in the WINGX software package
47] and finally checked with the PLATON software [48].
3-Nitro-4-ureido-furazan (1).
0.58 g (88%), 1-nitro-4-ureido-furazen was obtained as a
After drying in vacuum
ꢀ
1
All non-hydrogen atoms were refined anisotropically. The
hydrogen atom positions were located in a difference
Fourier map. DIAMOND plots are shown with thermal
ellipsoids at the 50% probability level. These data can be
obtained free of charge from The Cambridge
Crystallographic Data Centre. All chemicals were used as
supplied. Raman spectra were recorded in a glass tube with
a Bruker MultiRAM FT-Raman spectrometer (Bruker,
Germany) with Nd:YAG laser excitation up to 1000 mW
pale green powder. DSC (5°C min ): 179°C (m.p.),
ꢀ
1
182°C (dec.); IR (ATR, cm ): ṽ = 3319 (w), 3124 (w),
1593 (s), 1558 (m), 1484 (w), 1439 (m), 1291 (s), 1262
(s), 1134 (m), 1092 (s), 1040 (s), 975 (m), 846 (m), 816
(m), 783 (m), 754 (m), 720 (m); Raman (1064 nm,
ꢀ
1
500 mW, 25°C, cm ): ṽ = 3302 (2), 1693 (6), 1614 (3),
1583 (4), 1554 (7), 1469 (49), 1411 (6), 1365 (29), 1321
(7), 1122 (3), 1052 (2), 976 (6), 836 (20), 793 (3), 765
(3), 656 (5), 465 (2), 402 (5), 332 (6), 218 (6), 146 (16),
1
(
at 1064 nm). Infrared spectra were measured with a
PerkinElmer Spectrum BX-FTIR spectrometer
PerkinElmer, Germany) equipped with Smiths
85 (100); H NMR (CDCl ) δ = 9.46 (NH), 6.9 (br,
3
13
1
NH2); C{ H} NMR (CDCl ) δ = 154.8 (CNO ), 153.1
3
2
ꢀ
1
(
a
(CNH), 146.6 (CO); EA (C H N O , 173.09 g mol )
3 3 5 4
Dura/SamplIR II ATR device (Smiths, UK). All spectra
were recorded at ambient (25°C) temperature. NMR
spectra were recorded with a JEOL/Bruker instrument
Calc.: C 20.82; H 1.75; N 40.46%; Found: C 20.97; H
1.84; N 40.36%; Sensitivity (100 μm ≥ g.s. ≥ 50 μm) IS:
40 J; FS: 360 N; ESD: 1.5 J.
(
JEOL, Japan) and chemical shifts were determined with
3-Nitro-4-nitroureido-furazan (2). A mixture of fuming
nitric and sulfuric acid (each 2 mL) was cooled to 0°C. 1
(0.25 g; 1.44 mmol) was added slowly to this mixture.
The reaction was stirred at 0°C for 30 min, then allowed
to warm up to room temperature and stirred additionally
for 1 hr. Afterwards the mixture was poured on 30 g of
ice and extracted three times with 50 mL ethyl acetate.
The organic phases were washed twice with water and
one time with brine. Subsequently, the organic phases
were dried with magnesium sulfate and the solvent
removed on the rotary evaporator to obtain a pale yellow
powder. After recrystallization from acetonitrile, 0.28 g
(90%) of colorless pure 2 was obtained. DSC (5°C
1
13
respect to external Me Si ( H, 399.8 MHz,
1
C/H/N were performed with an Elemental Vario EL
Analyzer (Elementar, Germany). Melting and
decomposition points were measured using differential
C,
4
14
00.5 MHz) and MeNO ( N, 28.9 MHz). Analyses of
2
ꢀ
1
scanning calorimetry (DSC) at a heating rate of 5°C min
with an OZM Research differential thermal analysis 552-
Ex instrument. The sensitivity data were explored using a
BAM drop hammer and a BAM friction tester (Reichelt &
Partner, Germany) [49]. The energetic properties were
calculated using the computer code EXPLO6.03. It is based
on the chemical equilibrium, a steady state model of
detonation. It uses Becker–Kistiakowsky–Wilson’s
equation of state (BKW EOS) for gaseous detonation
products and Cowan–Fickett’s equation of state for solid
carbon. The input is based on the sum formula, calculated
heats of formation, and the maximum densities according
to their crystal structures (Table 1). All calculations were
carried out using the Gaussian G09 W (revision A.02)
program package. The heats of formations were calculated
by the atomization method based on CBS-4M electronic
enthalpies [50]. All calculations affecting the detonation
parameters were carried out using the program package
EXPLO5 6.03 [42,51].
ꢀ
1
ꢀ1
min ): 122°C (dec.); IR (ATR, cm ): ṽ = 3469 (w),
3446 (m), 3336 (m), 1710 (w), 1633 (s), 1520 (s), 1498
(m), 1435 (m), 1368 (s), 1347 (m), 1209 (m), 1107 (w),
1040 (m), 870 (w), 763 (w), 726 (w); Raman (1064 nm,
ꢀ
1
500 mW, 25°C, cm ): ṽ = 2247 (3), 1748 (16), 1722
(10), 1629 (9), 1611 (10), 1567 (10), 1532 (16), 1467
(73), 1415 (13), 1366 (76), 1051 (6), 973 (25), 894 (6),
843 (20), 765 (8), 597 (3), 567 (4), 458 (4), 372 (9), 328
1
(12), 239 (14), 96 (102); H NMR (CDCl ) δ = 11.08
3
13
1
(NHNO ), 10.67 (br, NHCO); C{ H} NMR (CDCl )
δ = 154.2 (CNO ), 145.0 (CNH), 144.8 (CO); N NMR
2
3
14
2
(CDCl3)
δ
=
ꢀ33 (CNO2), ꢀ42 (NHNO2); EA
ꢀ1
General synthesis of ureido derivatives (1, 3, 5, 6, and 7).
The 0.50 g of the corresponding amino furazan was poured
to 20 mL dry acetonitrile in a round bottom flask and
placed in an ice bath. CSI (1.10 molar equivalent for 1,
(218.09 g mol ) Calc.: C 16.52, H 0.92, N 38.54%;
Found: C 16.73, H 1.04, N 38.31%; Sensitivity
(100 μm ≥ g.s. ≥ 50 μm) IS: 4 J; FS: 360 N; ESD: 0.75 J.
3,4-Diureido-furazan (3).
0.87 g (94%) of 3 as a powder. DSC (5°C min ): 239°C
(dec.); IR (ATR, cm ): ṽ = 3418 (m), 3334 (m), 3129
(m), 1716 (s), 1694 (s), 1632 (w), 1576 (m), 1553 (s),
1477 (m), 1397 (m), 1360 (m), 1251 (m), 1131 (m), 1056
(m), 992 (w), 923 (w), 887 (w), 856 (m), 778 (m), 717
(m), 660 (w); Raman (1064 nm, 500 mW, 25°C, cm ):
ṽ = 3231 (4), 1699 (3), 1570 (3), 1342 (16), 1305 (4),
1279 (3), 1136 (4), 1057 (5), 1016 (100), 889 (4), 857
Drying in vacuum yielded
ꢀ
1
2
.10 molar equivalent for 3, 5, 6, and 7) was added slowly
at 0°C. The mixture was stirred at ambient temperature for
0 min and then cooled again to 0°C. Fifteen milliliter of
ꢀ
1
3
water was added very slowly at this temperature. After
warming the mixture to room temperature, it was stirred for
1
was removed under vacuum. The precipitate formed was
filtered off and washed with ice water.
ꢀ
1
h, while a precipitate was generated. The organic solvent
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2018
Energetic Ureido-Furazans
ꢀ
1
(
3), 681 (9), 556 (7), 537 (13), 362 (16), 179 (10), 123
(1064 nm, 500 mW, 25°C, cm ): ṽ = 2859 (26), 2084
(6), 2028 (3), 1692 (5), 1616 (5), 1497 (100), 1448 (75),
1397 (28), 1354 (42), 1308 (9), 1108 (6), 1053 (6), 980
1
(
17). H NMR (DMSO-D ) δ = 9.38 (NH), 6.8 (br, NH );
6
2
1
3
1
C{ H} NMR (DMSO-D ) δ = 154.8 (CNH), 146.6
6
ꢀ
1
(
CO); EA (C H N O , 186.13 g mol ) Calc.: C 25.81,
(7), 949 (5), 912 (9), 875 (13), 808 (7), 642 (4), 538 (4),
432 (4), 404 (4); H NMR (DMSO-D ) δ = 9.80 (s, NH),
9.60 (s, NH), 6.9 (br, NH ), 6.8 (br, NH ); C{ H}
4
6 6 3
1
H 3.25, N, 45.15%; Found: C 25.72, H 3.32, N 44.74%;
IS: 40 J; FS: 360 N; ESD: 1.5 J.
6
13
1
2
2
3
,4-Dinitroureido-furazan (4). Into a mixture of 2 mL of
fuming nitric acid and 2 mL of sulfuric acid, 3 (0.25 g;
.30 mmol) was added slowly at 0°C. The mixture was
NMR (DMSO-D ) δ = 154.2 (N(NO)C), 153.2 (ONNC),
6
152.9 (CNH), 149.2 (CNH), 148.4 (CO), 146.6 (CO); EA
ꢀ
1
1
(C H N O ; 298.05 g mol ): Calc.: C 22.79, H 2.55, N
6 6 10 5
stirred at this temperature for 30 min and an additional
hour at room temperature. Then, the reaction was poured
on 20 g of ice and extracted three times with 30 mL of
ethyl acetate. The combined organic layers were washed
twice with water and once with brine. After drying the
organic phases with magnesium sulfate, the solvent was
removed in vacuum to yield a colorless powder. After
recrystallization from acetonitrile, 0.32 g (90%) of
44.30%; found: C 23.10, H 2.45, N 43.75%.
0
0
3,3 -Diureido-4,4 -bifurazan (7). Compound 7 (1.39 g)
was obtained as colorless powder (91%). DSC
ꢀ
1
(5°C min ): 240°C (dec.); IR (ATR): ṽ = 3502 (w),
3283 (m), 3183 (w), 2360 (w), 1694 (s), 1599 (m), 1519
(s), 1455 (w), 1377 (m), 1289 (m), 1103 (m), 1038 (m),
990 (s), 921 (m), 871 (m), 795 (m), 716 (m); Raman
ꢀ
1
(1064 nm, 500 mW, 25°C, cm ): ṽ = 3286 (10), 2858
(11), 2553 (6), 2407 (6), 1700 (28), 1632 (100), 1601
(31), 1548 (52), 1525 (74), 1427 (75).1365 (8), 1251 (9),
1117 (40), 1051 (8), 1038 (8), 969 (13), 883 (17), 815
ꢀ
1
colorless pure 4 was obtained. DSC (5°C min ): 140°C
ꢀ
1
(
1
dec.); IR (ATR, cm ): ṽ = 3308(w), 2358 (w), 1746 (s),
601 (s), 1432 (s), 1377 (m), 1311 (m), 1280 (m), 1234
(
s), 1156 (m), 1085 (m), 982 (m), 932 (w), 871 (w), 839
(55), 660 (24), 585 (6), 544 (10), 530 (9), 463 (21), 443
1
(w), 771 (m), 744 (m), 704 (m); Raman (1064 nm,
(5), 367 (20), 286 (17), 221 (11); H NMR (DMSO-D
6
)
ꢀ
1
13
1
5
(
(
00 mW, 25°C, cm ): ṽ = 1739 (41), 1702 (37), 1618
δ = 9.63 (s, NH), 6.5 (br, NH
D ) δ = 154.3 (CNN), 151.9 (CNH), 140.3 (CO); EA
6
); C{ H} NMR (DMSO-
2
36), 1565 (84), 1523 (28), 1410 (50), 1339 (90), 1065
6), 1036 (12), 986 (100), 938 (11), 884 (54), 850 (18),
ꢀ
1
(C H N O , 254.17 g mol ): Calc.: C 28.35, H 2.38, N
6 6 8 4
7
4
71 (20), 724 (9), 600 (12), 502 (23), 470 (22), 456 (18),
18 (17), 381 (9), 308 (22), 229 (18), 204 (23); H NMR
44.09%; found: C 28.05, H 2.70, N 43.37%.
1
3-Nitro-4-ethoxycarbamoyl furazan (8).
Compound 2
(
CDCl ) δ = 13.5 (br, NHNO2), 10.93 (2H, CNH);
(0.50 g, 2.30 mmol) was dissolved in 10 mL ethanol. The
mixture was heated 5 min to reflux and cooled to room
temperature. The solvent was evaporated slowly yielding
3
1
1
3
4
1
C{ H} NMR (CDCl ) δ = 147.2 (CNH); 146.4 (CO),
3
N NMR (CDCl ) δ = ꢀ42 (NHNO ); EA (C H N O ,
3
2
4
4
8
7
ꢀ
1
ꢀ1
2
76.13
g
mol
)
Calc.:
C
17,40,
H
1,46,
N
8 (0.43 g) as colorless crystals (91%). DSC (5°C min ):
4
0.58%, Found: C 17.98, H 1.81, N 40.48%; Sensitivity
126°C (melt), 153°C (dec.); IR (ATR): ṽ = 3280 (w),
2984 (w), 1757 (m), 1728 (s), 1616 (m), 1565 (m), 1536
(s), 1466 (m), 1408 (m), 1371 (m), 1338 (s), 1303 (m),
1227 (s), 1197 (s), 1092 (m), 1058 (s), 1040 (m), 993
(m), 942 (m), 854 (m), 831 (s), 773 (m), 724 (w). Raman
(1064 nm, 500 mW, 25°C, cm ): ṽ = 3748 (6), 3008 (7),
2981 (23), 2964 (10), 2841 (23), 1753 (6), 1729
(14), 1580 (7), 1548 (7), 1538 (11), 1472 (100), 1409
(22), 1391 (17), 1372 (18), 1341 (36), 1306 (7), 1099
(10), 1067 (7), 1042 (12), 1010 (7), 995 (14), 947 (9),
899 (7), 854 (17), 832 (17), 763 (10), 594 (8), 558 (8),
(100 μm ≥ g.s. ≥ 50 μm) IS: 7 J; FS: 360 N; ESD: 0.7 J.
0
0
3
,3 -Diureido-4,4 -azoxyfurazan (5).
Compound
5
(
(
3
(
1
0.63 g) was obtained as yellow powder (88%). DSC
ꢀ
1
5°C, min ): 250°C (dec.); IR (ATR): ṽ = 3367 (w),
314 (w), 3208 (w), 2357 (w), 1737 (w), 1700 (s), 1637
m), 1594 (w), 1533 (s), 1477 (w), 1695 (s), 1347 (m),
260 (m), 1133 (w), 1051 (m), 993 (w), 942 (w), 886
w), 819 (m), 776 (w), 749 (w), 701 (w), 660 (w); Raman
ꢀ
1
(
(
(
ꢀ
1
1064 nm, 500 mW, 25°C, cm ): ṽ = 2859 (16), 2083
4), 2028 (3), 1485 (5), 1450 (100), 1427 (13), 1355 (18),
1
296 (5), 1259 (7), 999 (4), 948 (3), 929 (7), 806
465 (15), 450 (12), 440 (14), 425 (14), 414 (13), 309
1
1
(4), 538 (3), 466 (2); H NMR (DMSO-D ) δ = 9.43 (s,
(20), 287 (16), 177 (23), 84 (63). H NMR (DMSO-D
)
6
6
1
3
1
NH), 6.9 (br, NH2);
δ = 156.8 (CNN), 153.0 (CNH), 146.4 (CO); EA
C{ H} NMR (DMSO-D6)
δ = 9.73 (NH), 4.28 (q, 7.1 Hz, CH
2
), 1.31 (t, 7.1 Hz,
13
1
CH
); C{ H} NMR (DMSO-D
3
) δ = 154.8 (CNO ),
6
2
ꢀ
1
14
(C H N O , 282.06 g mol ): Calc.: C 24.75, H 2.42,
151.9 (CNH), 145.7 (CO), 62.9 (CH
2
), 13.6 (CH
); EA (C H N O ,
5 6 4 5
3
);
N
6
6 10 4
N: 48,10%; found: C 24.94, H 2.25, N 47.37%.
NMR (DMSO-D
202.13 g mol ): Calc.: C 29.71, H 2.99, N 27.72%,
found: C 29.41, H 3.75, N 28.08%.
6
) δ = ꢀ26 (CNO
2
0
0
ꢀ1
3
,3 -Diureido-4,4 -azofurazan (6). Compound 6 (0.37 g)
ꢀ
1
was obtained as orange powder (89%). DSC (5°C min ):
2
1
60°C (dec.); IR (ATR): ṽ = 3432 (m), 3291 (m), 3220 (w),
4-Amino-3-(5-amino-1,2,4-oxadiazolyl) furoxan (9).
Potassium bicarbonate (2.07 g, 20.72 mmol) was
dissolved in 40 mL water and 4-amino-3-aminooxim
furoxan (1.00 g, 6.28 mmol) was added. The reaction
717 (m), 1690 (vs), 1614 (m), 1538 (s), 1468 (m), 1392
(s), 1342 (m), 1302 (w), 1251 (w), 1169 (w), 1112 (w),
1
049 (w), 975 (w), 820 (m), 771 (w), 712 (m); Raman
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

T. S. Hermann, T. M. Klapötke, B. Krumm, and J. Stierstorfer
Vol 000
mixture was heated until a clear solution is obtained. After
cooling to room temperature cyanogen bromide (0.73 g,
17.9 mmol) 3,4-bis-aminooxime furoxan (1.44 g,
7.1 mmol) was added. The reaction mixture was heated
under reflux for 10 min forming a clear solution. After
cooling to 40°C cyanogen bromide (1.89 g, 17.85 mmol)
was added in portions. The reaction mixture was stirred
overnight at ambient temperature and subsequently
acidified with 2 M hydrochloric acid to pH 2. The
precipitate was filtered off and washed extensively with
water. A 0.93 g (54%) of 11 was obtained as brownish
powder. DSC (5°C min ): 273°C (dec.). IR (ATR):
ṽ = 3472 (w), 3340 (w), 3249 (w), 3177 (w), 1662 (s),
1608 (s), 1566 (m), 1529 (m), 1449 (m), 1416 (m), 1359
(w), 1259 (w), 1220 (w), 1112 (m), 1073 (w), 1050 (m),
1008 (w), 976 (w), 946 (m), 910 (w), 824 (s), 761 (m),
724 (m), 683 (m). Raman (1064 nm, 500 mV, 25°C)
ṽ = 2859 (20), 1661 (19), 1606 (7), 1569 (77), 1530 (24),
1509 (42), 1455 (8), 1425 (25), 1378 (22), 1220 (58),
1108 (16), 1099 (3), 1010 (8), 977 (59), 911 (11), 827
(13), 757 (42), 546 (6), 498 (12), 464 (11), 421 (18), 362
6
.91 mmol) was added in portions. The reaction mixture
was stirred overnight and then acidified with 2
M
hydrochloric acid. The precipitate was filtered off and
washed extensively with water and diethyl ether. A 0.62 g
(
54%) of 9 was obtained as yellowish brown powder.
ꢀ
1
DSC (5°C min ): 198°C (dec.). IR (ATR): ṽ = 3436 (w),
334 (w), 3168 (w), 1689 (m), 1635 (m), 1574 (w), 1537
s), 1494 (m), 1422 (w), 1350 (w), 1236 (w), 1161 (m),
3
(
ꢀ
1
1
6
078 (w), 1034 (m), 948 (m), 913 (w), 857 (m), 760 (m),
87 (m), 666 (m). Raman (1064 nm, 500 mV, 25°C)
ṽ = 1757 (6), 1609 (82), 1571 (46), 1558 (4), 1455 (12),
1
7
254 (5), 1219 (16), 1069 (8), 1053 (3), 955 (36), 827 (6),
51 (16), 669 (6), 556 (4), 504 (5), 449 (19), 406 (4), 375
(
(
26), 308 (3), 264 (10), 242 (2), 205 (16), 124 (3), 96
1
100). H NMR (DMSO-D ) δ = 8.4 (br, NH ), 6.5 (br,
6
2
13
1
NH2). C{ H} NMR (DMSO-D ) δ = 172.3 (CNO),
6
1
57.6 (Cring), 156.3 (CN(O)O), 101.7 (CNH ). EA
2
ꢀ
1
(C H N O , 184.12 g mol ): Calc.: C 26.09, H 2.19, N
(28), 314 (3), 304 (4), 283 (9), 272 (3), 244 (2), 214 (21),
4
4 6 3
1
4
5.65%: found: C 25.84, H 2.38, N 43.93%.
126 (100), 95 (8). H NMR (DMSO-D ) δ = 8.4 (br,
6
13
1
4
-Nitro-3-(5-amino-1,2,4-oxadiazolyl) furoxan (10).
For
NH
δ = 173.0 (CNH
(Cring), 144.7 (CNO), 106.7(CN(O)O). EA (C
2
), 8.3 (br, NH
).
2
C{ H} NMR (DMSO-D
)
6
the preparation of Caro’s acid, 10 mL of conc. sulfuric
acid was added slowly to 30% hydrogen peroxide at 0°C.
Compound 9 (0.5 g, 1.36 mmol) was dissolved in 5 mL
conc. sulfuric acid and slowly added to Caro’s acid,
while keeping the temperature between 0°C and 10°C.
The reaction mixture was heated slowly to 40°C and
stirred for 30 min. After cooling to ambient temperature,
the mixture was quenched with ice and water. After
extracting with ethyl acetate (3 × 30 mL), the combined
organic phases were washed with water (2 × 20 mL),
brine (1 × 20 mL) and dried over magnesium sulfate. The
solvent was removed under reduced pressure and
recrystallized from acetone. A 0.20 g (66%) of 10 was
2
), 159.6 (CNH
2
), 156.9 (Cring), 155.9
H N O ,
6 4 8 4
ꢀ
1
252.15 g mol ) Calc.: C 28.58, H 1.60, N 44.44%,
found: C 27.73, H 2.03, N 42.28%.
Acknowledgments. Financial support of this work by the
Ludwig-Maximilian University of Munich (LMU) and the
Office of Naval Research (ONR) under grant no. ONR.N00014-
16-1-2062 is gratefully acknowledged.
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obtained as yellow crystals. DSC (5°C min ): 188°C
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1
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δ = ꢀ35 (NO ) ppm. EA (C H N O , 214.10 g mol ):
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0
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet