Furazans with Azo Linkages: Stable CHNO Energetic Materials with High Densities, Highly Energetic Performance, and Low Impact and Friction Sensitivities

Article abstract of DOI:10.1002/chem.201601901

Various highly energetic azofurazan derivatives were synthesized by simple and efficient chemical routes. These nitrogen-rich materials were fully characterized by FTIR spectroscopy, elemental analysis, multinuclear NMR spectroscopy, and high-resolution mass spectrometry. Four of them were further confirmed structurally by single-crystal X-ray diffraction. These compounds exhibit high densities, ranging from 1.62 g cm^?3up to a remarkably high 2.12 g cm^?3for nitramine-substituted azofurazan DDAzF (2), which is the highest yet reported for an azofurazan-based CHNO energetic compound and is a consequence of the formation of strong intermolecular hydrogen-bonding networks. From the heats of formation, calculated with Gaussian 09, and the experimentally determined densities, the energetic performances (detonation pressure and velocities) of the materials were ascertained with EXPLO5 v6.02. The results suggest that azofurazan derivatives exhibit excellent detonation properties (detonation pressures of 21.8–46.1 GPa and detonation velocities of 6602–10 114 m s^?1) and relatively low impact and friction sensitivities (6.0–80 J and 80–360 N, respectively). In particular, they have low electrostatic spark sensitivities (0.13–1.05 J). These properties, together with their high nitrogen contents, make them potential candidates as mechanically insensitive energetic materials with high-explosive performance.

Full text of DOI:10.1002/chem.201601901

DOI: 10.1002/chem.201601901
Full Paper
&
Energetic Materials |Hot Paper|
Furazans with Azo Linkages: Stable CHNO Energetic Materials
with High Densities, Highly Energetic Performance, and Low
Impact and Friction Sensitivities
Yanyang Qu,* Qun Zeng, Jun Wang, Qing Ma, Hongzhen Li, Haibo Li,* and
Guangcheng Yang[a]
Abstract: Various highly energetic azofurazan derivatives
were synthesized by simple and efficient chemical routes.
These nitrogen-rich materials were fully characterized by
FTIR spectroscopy, elemental analysis, multinuclear NMR
spectroscopy, and high-resolution mass spectrometry. Four
of them were further confirmed structurally by single-crystal
X-ray diffraction. These compounds exhibit high densities,
an 09, and the experimentally determined densities, the en-
ergetic performances (detonation pressure and velocities) of
the materials were ascertained with EXPLO5 v6.02. The re-
sults suggest that azofurazan derivatives exhibit excellent
detonation properties (detonation pressures of 21.8–
46.1 GPa and detonation velocities of 6602–10114 msꢀ1) and
relatively low impact and friction sensitivities (6.0–80 J and
80–360 N, respectively). In particular, they have low electro-
static spark sensitivities (0.13–1.05 J). These properties, to-
gether with their high nitrogen contents, make them poten-
tial candidates as mechanically insensitive energetic materi-
als with high-explosive performance.
ranging from 1.62 gcmꢀ3 up to
a remarkably high
2.12 gcmꢀ3 for nitramine-substituted azofurazan DDAzF (2),
which is the highest yet reported for an azofurazan-based
CHNO energetic compound and is a consequence of the for-
mation of strong intermolecular hydrogen-bonding net-
works. From the heats of formation, calculated with Gaussi-
Introduction
oxygen needed for oxidation of the fuel portion to enhance
combustion and therefore supports the release of large
amounts of energy. Recently, the development of nitrogen-rich
energetic materials has been recognized as one of the most ef-
fective strategies for the design and synthesis of HEDMs.[2] In
addition, the importance of ring strain and the presence of Nꢀ
N, CꢀN, and NꢀO bonds for the effectiveness of HEDMs has
been recognized. However, excessive introduction of functional
groups into a limited backbone leads to increased sensitivity
to mechanical stimulation. Therefore, seeking a balance be-
tween high performance and stability is the main challenge in
the design of advanced HEDMs. The field of chemistry related
to HEDMs must expand the boundaries of the energy capacity
of the compounds, which requires new classes of functional-
ized compounds,[3] advanced theoretical prediction tech-
niques,[4] and new synthetic strategies.[5]
Traditional high energy density materials (HEDMs) used for ci-
vilian and military applications developed over the last two
centuries and still widely used include 2,4,6-trinitrotolune
(TNT), cyclo-1,3,5-trimethylene-2,4,6-trinitamine (RDX), 1,3,5,7-
tetranitrotetraazacyclooctane (HMX), and pentaerythritol tetra-
nitrate (PETN). However, there is ongoing research and interest
in the synthesis of HEDMs that are environmentally benign
and combine high performance with low sensitivity, a task
which poses particular challenges to the synthetic organic
chemist. The desirable characteristics of new HEDMs include
high density, positive heats of formation (HOF), a positive
oxygen balance (OB), high detonation velocity and pressure,
high thermal stability, simple synthesis, low sensitivity toward
external forces such as impact and friction, and environmental
friendliness.[1] The traditional strategy for designing new
HEDMs involves incorporating both fuel and oxidizer proper-
ties into a single molecule. The oxidizer part provides the
Unlike the traditionally designed energetic materials, in
which the fuel and oxidizing characteristics are the sole factors
determining their performance, nitrogen-rich compounds have
some unique properties such as high heats of formation, sig-
nificant gas release in the form of environmentally benign ni-
trogen, and commonly include moieties such as five-mem-
bered azole and six-membered azine rings. Improvements in
the OB have been achieved with the development of the oxa-
diazoles. Of these, 1,2,5-oxadiazole (furazan I, Figure 1) is an
appropriate choice as the core structure of new HEDMs due to
its high heat of formation (185 kJmolꢀ1) and release of envi-
[a] Dr. Y. Qu, Dr. Q. Zeng, Prof. J. Wang, Dr. Q. Ma, Prof. H. Li, Prof. H. Li,
Prof. G. Yang
Institute of Chemical Materials, CAEP
P. O. Box 919-311 Mianyang Sichun, 621900 (P. R. China)
E-mail: quyy131226@caep.cn
lihb99@caep.cn
Supporting information and ORCID(s) from the author(s) for this article is
available on the WWW under http://dx.doi.org/10.1002/chem.201601901.
Chem. Eur. J. 2016, 22, 1 – 7
1
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
azofurazan-based energetic materials with groups that en-
hance the energetic characteristics of the molecule [e.g., NH2,
CN, triazole, tetrazolium, and 1,2,4-oxadiazole (II)].
Results and Discussion
Figure 1. Calculated gas-phase heats of formation for oxadiazole and azole
compounds.[6]
Scheme 1 shows an overview of the synthetic steps to form
the various azofurazans. The furazan moiety has been found to
be a vital constituent of HEDMs, and its presence greatly con-
tributes to the overall energetic performance. Modeling studies
show that when a nitro group is replaced by a furazan group
in energetic compounds, the density, heat of formation, and
ronmentally benign gaseous nitrogen as one of the main de-
composition products. In addition, several azo-based HEDMs
have been investigated in recent years,[7] and the presence of
an azo (ꢀN=Nꢀ) moiety generally imparts a high endothermic
heat of formation to a compound. Thus, the decomposition
energy is largely derived from this source rather than from the
fuel–oxidizer reaction. We expected that linking furazans sub-
stituted in the 3,3’-positions with energetic functional groups
via azo linkages could be a promising new strategy for tailor-
ing new energetic compounds that display physical and ener-
getic properties such as higher detonation parameters and
lower sensitivity toward impact and friction. To the best of our
knowledge, herein we report the first synthesis of a series of
detonation velocity are increased by about 0.06–0.08 gcmꢀ3
,
200 kJmolꢀ1, and 300 msꢀ1, respectively.[8] Energetic materials
based on triazoles and tetrazoles show the desirable properties
of high N content and thermal stability (due to aromaticity).
These properties, together with the high heats of formation of
oxadiazole heterocycles suggested that linking these moieties
to the furazan backbone could be an appropriate strategy to
improve the energetic performance of novel HEDMs. Malononi-
trile was chosen as a useful precursor for the preparation of
the azofurazan energetic materials containing the core furazan
Scheme 1. Structures and synthetic routes of azofurazan compounds. a) NaNO2, NH2OH·HCl, 08C; 1008C, 72%; b) PbO2, AcOH, 08C, 55%; c) Semicarbazide,
TFA, 1208C, 46%; d) BrCN, KHCO3, 308C, 97%; e) Ac2O, 1208C, 89%; f) Trifluoroacetic anhydride, 1208C, 66%; g) KMnO4, conc. HCl and CH3CN, 208C, 62%;
h) AcOH, Ac2O and HNO3, 08C, 78%; i) KMnO4, 20% HCl, 208C, 68–90%; j) 1,3-diaminourea (DAU), H2O, 1008C, 67%; k) (EtO)3CH, BF3·Et2O, 1208C, 86%; l) N2H4,
CH3CN, 308C, 96%; m) NaNO2, 2% HCl, 308C, 92%; n) Ac2O, 1208C, 60%.
&
&
Chem. Eur. J. 2016, 22, 1 – 7
www.chemeurj.org
2
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
scaffold. 4-Amino-N-hydroxyfurazan-3-carboximide (AFA), 4-
amino-1,2,5-oxadiazole-3-carbonitrile (13), and 4-(1H-tetrazol-5-
yl)-furazan-3-amine (17) were prepared on the basis of litera-
ture methods.[9] The formation of azo-bridged compounds by
oxidative coupling between the amino groups of furazan inter-
mediates such as 13 is well known.[10] For example, treatment
of intermediates 13 and 17 with one equivalent of alkaline po-
tassium permanganate (KMnO4) in 20% HCl at room tempera-
ture yielded 3,3’-dicyano-4,4’-azofurazan DCAzF (10) and tetra-
zole-substituted azofurazan DTAzF (6) in 90 and 70% yields, re-
spectively. Although 10 and 6 have been previously reported,
their full physical and detonation properties were not stud-
ied.[11] In addition, the oxime precursor AFA can be treated
with a wide variety of reactants to form a whole new set of
previously unreported azofurazan compounds 1–4, 7, and 8
via intermediates 19–23 (Scheme 1). Thus cyanogen bromide,
acetic anhydride, trifluoroacetic anhydride, triethyl orthofor-
mate, and carbohydrazide give intermediate compounds 19,
20, 21, 22, and 23, respectively (Scheme 1). Further treatment
of 13 with semicarbazide leads to the formation of 4-(5-amino-
1,3,4-oxadiazol-2-yl)-1,2,5-oxadiazol-3-amine (14).
The reaction of 10 with semicarbazide produced azofurazan
DIAzF (11) as the main product in 72% yield. Oxidation of 18
with one equivalent of KMnO4 in 20% HCl at room tempera-
ture afforded DFAzF (1) in 76% yield as a yellow solid. In addi-
tion, DNAzF (12) was also prepared from DHAzF (8) in two
steps via N-amino imine intermediate 24 in 56% yield. An anal-
ogous method gave the corresponding azo-bridged furazans
3–11 in moderate to good yields (Scheme 1). Nitration of
1 with a mixture of nitric acid and acetic anhydride at 108C
gave DDAzF (2) in 89% yield (Scheme 1).
Suitable crystals of azofurazans 3, 8, 9, and 21 were grown
by slow evaporation of the solvent of solutions in methanol/
acetone, acetonitrile, dimethyl sulfoxide, and ethyl acetate, re-
spectively, at room temperature. Their structures are shown in
Figure 2. Data collection and refinement parameters are given
in Table S2 (see Supporting Information). The structures of the
newly prepared energetic compounds are supported by FTIR
spectroscopy, 1H and 13C NMR spectroscopy, high-resolution
mass spectrometry, and elemental analysis (see the Supporting
Information). 15N NMR spectra were recorded only for DF3AzF
(4), DHAzF (8), and DXAzF (9) in [D6]DMSO solutions. Chemical
shifts are given in Figure 3 with respect to nitromethane as ex-
ternal standard. Azofurazan 8 shows five signals because of its
symmetrical structure, and the signal for the azo nitrogen sig-
nals occurs at 60 ppm. The furazan nitrogen signals are ob-
served downfield relative to the signals for N4 and N5 of the
isoxazole ring. However, the signals from the furazan nitrogen
atoms in DF3AzF (4) are observed between about ꢀ10 and
10 ppm, which may be due to the impact of the CF3 groups.
The heat of formation DHf,solid is an important parameter that
must be considered when designing energetic materials. All
enthalpy calculations were performed with the Gaussian 09
software package. By using the isodesmic-reaction approach
(see Supporting Information), the heats of formation of the
species can be easily extracted. With the exception of the neg-
ative heat of formation of DF3AzF (4), all of the other synthe-
Figure 2. Single-crystal X-ray structures of a) DMAzF (3), b) DHAzF (8),
c) DXAzF (9), and d) 21.
sized compounds exhibit positive heats of formation that are
considerably higher than those of RDX and HMX (Table 1). The
heats of formation of the azofurazans range from
684.1 kJmolꢀ1 for DIAzF (11) to 1224.3 kJmolꢀ1 for DTAzF (6),
and most of them have values in the range 700–800 kJmolꢀ1.
Density is an important property contributing to the detona-
tion performance of energetic materials. The densities of the
new azofurazans were measured with a gas pycnometer at am-
bient temperature and were found to be between 1.68 gcmꢀ3
for DOAzF (7) and 2.12 gcmꢀ3 for DDAzF (2). (We attempted
Chem. Eur. J. 2016, 22, 1 – 7
www.chemeurj.org
3
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
the handling of explosive materials, used approximately 20 mg
samples; the capacitance was 30000 pF with an electrode gap
of 0.5 mm. For all of the compounds, the impact sensitivities
range from those of the relatively insensitive azofurazans
DCAzF (10), DHAzF (8), and both DMnAzF (5) and DNAzF (12),
with IS values of 7.5, 12.5, and 40 J, respectively (Table 1), to
the very insensitive compounds DFAzF (1), DMAzF (3), DF3AzF
(4), DIAzF (11), and DOAzF (7) with ISꢁ80 J. DDAzF (2) is over-
all the most mechanically sensitive compound, with an impact
sensitivity of 6.0 J, friction sensitivity of 40 N, and electrical
spark sensitivity of 0.51 J. Tetrazole-substituted azofurazan
DTAzF (6) has the highest impact sensitivity (IS=4.7 J), is also
quite friction sensitive (FS=96 N), and has an electrical spark
sensitivity of 0.13 J. Overall, most of the compounds exhibit
improved sensitivity parameters compared to the common ex-
plosive RDX (IS=7.4 J, FS=120 N, ESD=0.2 J).
The phase transitions and thermal stabilities of all com-
pounds were determined by differential scanning calorimetry
(DSC) at a scan rate of 108Cminꢀ1 (Table 1; see Supporting In-
formation for further details and scans). DHAzF (8) and DMAzF
(3) are the only compounds that melt prior to decomposition,
at 142 and 1318C, respectively. Both DFAzF (1) and DTAzF (6)
have sharp exothermic peaks, which indicate rapid decomposi-
tion. Compound DFAzF (1), with an onset decomposition tem-
perature of 246.858C, exhibits an exothermic peak at 267.298C,
which is 108C higher than that of DTAzF (6). However, DNAzF
(12) has a wider exothermicity temperature range with an
onset decomposition temperature of 179.298C and an exother-
mic peak maximum at 308.598C. Tetrazole- and cyano-substi-
tuted azofurazans DTAzF (6) and DF3AzF (4) decomposed at
2588C and 2408C, respectively. Surprisingly, nitramino com-
pound DDAzF (2), which was shown to be a powerful energet-
ic material with high detonation velocity, detonation pressure,
and heat of formation, decomposes at 3178C. With the excep-
tion of the triazole-substituted analogues DMnAzF (5) and
DNAzF (12) (Tdsc =350 and 3098C, respectively), other deriva-
Figure 3. 15N NMR spectra of DXAzF (9), DHAzF (8), and DF3AzF (4).
to crystallize compound 2 using different solvents, but failed
to obtain a single-crystal structure.) The densities of most ma-
terials are comparable to those of currently used explosives
RDX (1.82 gcmꢀ3) and HMX (1.91 gcmꢀ3). The remarkably high
density of DDAzF (2) arises from the presence of the nitramino
groups, and it is among the highest for CHNO explosives, such
as 5,5’-bis(trinitromethyl)-3,3’-bis(1,2,4-oxadiazole), having den-
sities higher than 2.00 gcmꢀ3.
The impact sensitivities (IS) and friction sensitivities (FS) of
the compounds were determined with a standard BAM Fall
Hammer and a BAM Friction Apparatus, respectively. The elec-
trical spark sensitivity tests (ESD, electrostatic discharge), which
provide a measure of the electrostatic hazards associated with
Table 1. Physical properties and detonation parameters.
Tdsc [oC][a]
1 [g/cm3][b]
fHm [kJ/mol][c]
OB [%][d]
vDet [m/s][e]
P [GPa][f]
IS [J][g]
FS [N][h]
ESD [J][i]
~
DFAzF
DHAzF
DMAzF
DF3AzF
DMnAzF
DCAzF
DTAzF
DIAzF
267
259
271
240
350
234
258
233
–
241
309
317
206
282
1.85
711.2
ꢀ67.45
ꢀ68.85
ꢀ92.12
ꢀ58.44
ꢀ97.59
ꢀ74.07
ꢀ58.27
ꢀ67.45
ꢀ63.45
ꢀ66.28
ꢀ82.40
ꢀ92.10
ꢀ21.6
8445
7685
7781
6602
8482
7640
8477
8323
–
7774
8458
10114
8977
9221
28.3
22.7
22.6
24.3
26.4
21.8
28.0
27.3
–
22.4
26.2
46.1
35.1
39.2
ꢁ80
12.5
ꢁ80
ꢁ80
40
7.5
4.7
ꢁ80
ꢁ80
ꢁ80
40
ꢁ360
ꢁ360
80
ꢁ360
80
ꢁ360
96
ꢁ360
120
252
ꢁ360
80
120
120
0.68
0.51
0.78
0.87
0.67
0.39
0.13
1.05
0.85
0.73
0.65
0.51
0.20
0.10
1.68/1.79[j]
1.75/1.65[j]
1.94
832.9
696.5
ꢀ488.6
864.3
933.9
1224.3
684.1
–
769.9
920.8
1038.0
92.6
1.81
1.62[j]
1.69/1.75[j]
1.83
DXAzF
DOAzF
DNAzF
DDAzF
RDX[j]
1.57[j]
1.68
1.79
2.12
1.82
1.94
6.0
7.4
7.0
HMX[j]
116.1
ꢀ21.6
[a] Decomposition temperature under nitrogen gas (DSC, 108C minꢀ1). [b] Density measured with a gas pycnometer (258C). [c] Heat of formation.
[d] Oxygen balance (OB) is the index of the deficiency or excess of oxygen in a compound required to convert all carbon to carbon dioxide and all hydro-
gen into water; for a compound with the molecular formula of CaHbNcOd, OB/%=1600[(dꢀ2aꢀb/2)/M]. [e] Detonation velocity (calculated with EXPLO5
v6.02). [f] Detonation pressure (calculated with EXPLO5 v6.02). [g] Impact sensitivity measured with a 5.0 kg hammer. [h] Friction sensitivity. [i] Electrical
spark sensitivity. [j] Crystal density. [j] From ref. [7a].
&
&
Chem. Eur. J. 2016, 22, 1 – 7
www.chemeurj.org
4
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
tives are less thermally stable with decomposition tempera-
tures below 3008C (Tdsc =2348C–2718C).
cellent detonation properties, with calculated detonation pres-
sures of P=21.8–46.1 GPa and detonation velocities of vDet
=
The experimental densities of these compounds range from
1.22 gcmꢀ3 to 2.12 gcmꢀ3 and are comparable to those of cur-
rently used energetic materials such as RDX (1.82 gcmꢀ3) and
(HMX, 1.91 gcmꢀ3). The remarkably high density of compound
2 (2.12 gcmꢀ3 at 258C, measured with a gas pycnometer) is
noteworthy, and is the highest value yet reported for an azo-
furazan-based CHNO energetic material. Other reported exam-
6602–10114 msꢀ1. These azofurazans have acceptable impact
and friction sensitivities in the ranges of 4.7–80 J and 80–
360 N, respectively. The electrostatic spark sensitivities are also
improved over those of RDX and HMX, and range from 0.13 to
1.05 J. In conclusion, the acceptable impact and friction sensi-
tivities of these novel azofurazan derivatives, coupled with
their high thermal stability, make them potential candidates
for future applications as high-performance CHNO energetic
materials.
ples include 4,4’-bis(nitramino)azofurazan (150 K, 1.957 gcmꢀ3
)
and 4,4’-bis(nitramino)azoxyfurazan (173 K, 2.020 gcmꢀ3).[12]
The higher density of 2 may be attributed to the nitramino
group being involved in multiple intermolecular hydrogen-
bonding interactions and the conjugate planar structure.
In addition to the heat of formation and the impact and fric-
tion sensitivities, the electrical spark sensitivities and the deto-
nation properties also play a major role in the design and de-
velopment of new energetic materials. The ESDs from this
work are listed in Table 1 and are compared with those of RDX
and HMX. Most of them are greater than 0.2 J and thus much
higher than those of RDX and HMX, except for DTAzF (6).
These properties indicate that the azo-linked furazan structure
plays a more important role in increasing the stability and de-
creasing the sensitivity of the molecule than the fuel and oxi-
dizing systems. With heats of formation and experimental den-
sities in hand, the detonation pressures P and velocities vDet
were calculated by using EXPLO5 v6.02 (Table 1). The calculat-
ed detonation pressures and velocities of the azofurazan deriv-
atives lie between 21.8 GPa for DCAzF (10) and 46.1 GPa for
DDAzF (2), and between 6602 msꢀ1 for DF3AzF (4) and
10114 msꢀ1 for nitramine (2). In contrast, RDX and HMX have
detonation pressures of 35.2 and 39.6 GPa and detonation ve-
locities of 8748 and 9059 msꢀ1, respectively. The significantly
improved detonation pressures and velocities of azofurazan 2,
coupled with the rather high thermal stabilities of the energet-
ic materials, especially of the triazole-substituted derivatives 5
and 12, suggest that these newly developed nitrogen- and
oxygen-rich azofurazan materials may be attractive candidates
for energetic applications.
Experimental Section
Safety precautions
Although none of the compounds described has exploded or deto-
nated, manipulations must be done with appropriate standard
safety precautions in a hood behind a safety shield with eye pro-
tection and leather gloves. Mechanical treatments of these ener-
getic materials involving scratching or scraping must be avoided.
All of these azofurazans were very stable on prolonged storage at
room temperature.
General methods
Decomposition temperatures were recorded with a differential
scanning calorimeter (TA Instruments Q10) at a scan rate of
108Cminꢀ1. The 1H and 13C NMR spectra were collected with
a Bruker AVANCE 300 NMR spectrometer operating at 300.13 and
75.48 MHz, respectively. A Bruker AVANCE 500 NMR spectrometer
operating at 50.69 MHz was used to collect 15N spectra. [D6]DMSO
was employed as the solvent and locking solvent. Chemical shifts
are given relative to Me4Si for H and 13C spectra and MeNO2 for
1
15N spectra. Elemental analyses (C, H, N) was performed on a CE-
440 Elemental Analyzer. Impact and friction sensitivity measure-
ments were done with a standard BAM Fall Hammer and a BAM
Friction Apparatus. The FTIR spectra of the solid samples were re-
corded by using KBr pellets with a Bio-Rad Model 3000 FTS spec-
trometer. Densities were determined at room temperature by em-
ploying a Micromeritics AccuPyc 1340 gas pycnometer.
Theoretical study
Conclusion
All calculations were performed with Gaussian 09. Geometric opti-
mization of the structures was carried out by using the DFT/M06-
2X functional with the 6-311+G(d) basis set. The optimized struc-
tures were conformed to be true local energy minima on the po-
tential-energy surface by frequency analyses at the same level. Ac-
cording to the isodesmic-reaction approach, the gas-phase enthal-
pies of formation were computed. The enthalpies of reaction were
obtained by combining the M06-2X/6-311+G(d) energy difference
for the reactions, the scaled zero-point energies, and other thermal
factors. Thus, the gas-phase enthalpy of the species under study
can be extracted.
A series of novel azofurazan derivatives were prepared starting
from the parent compound 4-amino-N’-hydroxy-furazan-3-car-
boximide. Their energetic properties were obtained on the
basis of experimentally determined densities and enthalpies of
formation determined with Gaussian 09. These compounds ex-
hibit good thermal stabilities and, with the exception of 4,
large positive heats of formation, considerably in excess of
those of the common energetic materials RDX and HMX. The
experimentally derived densities are high and lie between
1.62 gcmꢀ3 for cyano-substituted 10 and 2.12 gcmꢀ3 for nitra-
mine 2. The remarkably high density of 2 is the highest yet re-
ported for an azofurazan-based CHNO energetic compound
and is a consequence of the formation of strong intermolecu-
lar hydrogen-bonding networks between the amino hydrogen
and the nitro oxygen atoms. The new compounds exhibit ex-
Solid-state heats of formation of the resulting compounds can be
determined by subtracting the heats of sublimation from the gas-
phase heats of formation [Eq. (1)]:
DHf,solid ¼ DHf,gasꢀDHsub
ð1Þ
Chem. Eur. J. 2016, 22, 1 – 7
www.chemeurj.org
5
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
127, 12537–12543; d) M. Smiglak, A. Metlen, R. D. Rogers, Acc. Chem.
Res. 2007, 40, 1182–1192; e) R. P. Singh, R. D. Verma, D. T. Meshri, J. M.
Shreeve, Angew. Chem. Int. Ed. 2006, 45, 3584–3601; Angew. Chem.
2006, 118, 3664–3682; f) C. B. Jones, R. Haiges, T. Schroer, K. O. Christe,
Angew. Chem. Int. Ed. 2006, 45, 4981–4984; Angew. Chem. 2006, 118,
5103–5106; g) R. Wang, Y. Guo, Z. Zeng, B. Twamley, J. M. Shreeve,
Chem. Eur. J. 2009, 15, 2625–2634.
Politzer and co-workers found that the enthalpy of sublimation of
energetic compounds correlates well with the molecular surface
area and electrostatic interaction index ns2tot according to Equa-
tion (2):[13]
DHsub ¼ aA2 þ bðns2totÞ0:5 þ c
ð2Þ
[3] For some examples see: a) P. Yin, D. A. Parrish, J. M. Shreeve, J. Am.
Chem. Soc. 2015, 137, 4778–4786; b) H. X. Gao, J. M. Shreeve, Angew.
Chem. Int. Ed. 2015, 54, 6335–6338; Angew. Chem. 2015, 127, 6433–
where A is the surface area of the 0.001 bohrꢀ3 isosurface for the
electronic density of the molecule, v the degree of balance be-
tween the positive and negative potentials on the isosurface, and
s2tot is a measure of the variability of the electrostatic potential on
the molecular surface. The coefficients a, b, and c were determined
to be a=2.670ꢁ10ꢀ4 kcalmolꢀ1 Aꢀ4, b=1.650 kcalmolꢀ1, and c=
2.966 kcalmolꢀ1 from a calculation of the values of DHsub by Byrd
and co-workers.[14a] The descriptors A, v, and s2tot were obtained ac-
cording to the computational procedures described by Bulat and
co-workers.[14b]
´
6436; c) M. A. Kettner, K. Karaghiosoff, T. M. Klapçtke, M. Suceska, S.
Wunder, Chem. Eur. J. 2014, 20, 7622–7631.
[4] a) K. Baum, N. V. Nguyen, R. Gilardi, J. L. Flippen-Anderson, C. George, J.
Org. Chem. 1992, 57, 3026–3030; b) K. Baum, S. S. Bigelow, N. V.
Nguyen, T. A. Archibald, R. Gilardi, J. L. Flippen-Anderson, C. George, J.
Org. Chem. 1992, 57, 235–241.
[5] Z. X. Chen, H. M. Xiao, Propellants Explos. Pyrotech. 2014, 39, 487–495.
[6] a) H. Wei, J. H. Zhang, C. L. He, J. M. Shreeve, Chem. Eur. J. 2015, 21,
8607–8612; b) J. H. Zhang, J. M. Shreeve, J. Am. Chem. Soc. 2014, 136,
4437–4445.
[7] For some examples see: a) T. T. Vo, J. H. Zhang, D. A. Parrish, B. Twamley,
J. M. Shreeve, J. Am. Chem. Soc. 2013, 135, 11787–11790; b) V. Thottem-
pudi, H. X. Gao, J. M. Shreeve, J. Am. Chem. Soc. 2011, 133, 6464–6471;
c) Y. C. Li, C. Qi, S. H. Li, H. J. Zhang, C. H. Sun, Y. Z. Yu, S. P. Pang, J. Am.
Chem. Soc. 2010, 132, 12172–12173; d) T. M. Klapotke, D. G. Piercey,
Inorg. Chem. 2011, 50, 2732–2734; e) P. Yin, D. A. Parrish, J. M. Shreeve,
Chem. Eur. J. 2014, 20, 6707–6712; f) L. H. Zhen, L. J. Shan, H. Ming,
Z. X. Qing, Chin. J. Org. Chem. 2009, 29, 798–801; g) L. Qing, H. J. Xuan,
G. Y. Yuan, C. Y. Li, Chin. J. Energ. Mater. 2008, 16, 53–55; h) L. H. Zhen,
H. Ming, H. Y. Gang, D. H. Shan, L. J. Shan, Chin. J. Energ. Mater. 2005,
13, 192–195.
[8] a) A. B. Sheremeteev, T. S. Pivina, in the proceedings of the 27th Interna-
tional Annual Conference of ICT, Karlsruhe, Germany, 1996, pp. 1–13;
b) A. B. Sheremeteev, V. O. Kulagina, in the proceedings of the 22th Inter-
national Pyrotechnics Seminar, Colorado, USA, 1996, pp. 377–388.
[9] a) V. G. Andrianov, A. V. Eremeev, Khimiya 1994, 693–696; b) J. H. Come,
J. Green, C. Marhefka, S. L. Harbeson, L. Pham, PCT Int. Appl. 2005,
WO2005019190; c) O. M. Suleimenov, T. K. Ha, Chem. Phys. Lett. 1998,
290, 451–460; d) H. Martinez, Z. Zheng, W. R. Dolbier, Jr., J. Fluorine
Chem. 2012, 143, 112–122; e) L. Hui, Y. Q. Qian, W. B. Zhou, G. Z. Xue, L.
Yin, Chin. J. Energ. Mater. 2013, 21, 821–824.
Therefore, the expression for the solid-state enthalpy of formation
becomes Equation (3):
DHf,solid ¼ DHf,gasꢀaA2 þ bðns2totÞ0:5 þ c
ð3Þ
Acknowledgements
The authors gratefully acknowledge the support of the Nation-
al Natural Science Foundation of China (No. 11402240) and the
CAEP Foundation (No. 2014B0302038). We are also grateful for
the support of the comprehensive training platform in the spe-
cialized laboratory, College of Chemistry, Sichuan University.
We acknowledge the considerable assistance of Jinpeng Shen,
Yuntao Yang, Shaojun Yu, and Yinshuang Sun for carrying out
the IS, FS, and thermal performance tests. We are also indebt-
ed to Dr. Jie Sun for considerable assistance with the crystal
structure determinations.
[10] a) Q. Zhang, J. M. Shreeve, Angew. Chem. Int. Ed. 2013, 52, 8792–8794;
Angew. Chem. 2013, 125, 8954–8956; b) X. Xiao, G. Z. Xue, L. Qing, X.
Cheng, W. Wei, S. H. Peng, B. F. Qiang, Chin. J. Energ. Mater. 2013, 21,
173–179; c) Y. X. Tang, H. W. Yang, B. Wu, X. H. Jun, C. X. Lu, G. B.
Cheng, Angew. Chem. Int. Ed. 2013, 52, 4875–4877; Angew. Chem. 2013,
125, 4975–4977.
Keywords: azo compounds · density functional calculations ·
energetic materials · heterocycles · synthetic methods
[11] a) P. W. Leonard, D. E. Chavez, P. F. Pagoria, D. L. Parrish, Propellants
Explos. Pyrotech. 2011, 36, 233–239; b) F. Y. Jie, W. B. Zhou, Z. Y. Shui,
J. S. Yuan, H. Huan, Chin. J. Energ. Mater. 2009, 17, 385–388.
[12] J. H. Zhang, J. M. Shreeve, J. Phys. Chem. C 2015, 119, 12887–12895.
[13] a) P. Politzer, Y. Ma, P. Lane, M. C. Concha, Int. J. Quantum Chem. 2005,
105, 341–347; b) P. Politzer, J. S. Murray, M. E. Grice, M. Desalvo, E.
Miller, Mol. Phys. 1997, 91, 923–928.
[14] a) E. F. C. Byrd, B. M. Rice, J. Phys. Chem. A 2006, 110, 1005–1013; b) F. A.
Bulat, A. Toro-Labbꢂ, T. Brinck, J. S. Murray, P. Politzer, J. Mol. Model.
2010, 16, 1679–1691.
[1] a) M. B. Talawar, R. Sivabalan, T. Mukundan, H. Muthurajan, A. K. Sikder,
B. R. Gandhe, A. S. Rao, J. Hazard. Mater. 2009, 161, 589–607; b) H. W.
Qiu, V. Stepanov, A. R. DiStasio, T. M. Chou, W. Y. Lee, J. Hazard. Mater.
2011, 185, 489–493; c) Y. Bayat, M. Eghdamtalab, V. Zeynali, J. Energ.
Mater. 2010, 28, 273–284; d) Q. Zhang, J. M. Shreeve, Chem. Rev. 2014,
114, 10527–10574; e) D. Fischer, T. M. Klapçtke, J. Tierstorfer, Angew.
Chem. Int. Ed. 2014, 53, 8172–8175; Angew. Chem. 2014, 126, 8311–
8314; f) A. A. Dippold, T. M. Klapçtke, J. Am. Chem. Soc. 2013, 135,
9931–9938.
[2] a) J. P. Agrawal, Prog. Energy Combust. Sci. 1998, 24, 1–30; b) D. E.
Chavez, M. A. Hiskey, R. D. Gilardi, Angew. Chem. Int. Ed. 2000, 39, 1791–
1793; Angew. Chem. 2000, 112, 1861–1863; c) M. H. V. Huynh, M. A.
Hiskey, D. E. Chavez, D. L. Naud, R. D. Gilardi, J. Am. Chem. Soc. 2005,
Received: April 22, 2016
Published online on && &&, 0000
&
&
Chem. Eur. J. 2016, 22, 1 – 7
www.chemeurj.org
6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
FULL PAPER
Mechanically insensitive energetic ma-
terials: Various azofurazans (see figure;
Y = N or C) were prepared from the
parent compound 4-amino-N’-hydroxy-
furazan-3-carboximiide and their ener-
getic properties were determined.
&
Energetic Materials
Y. Qu,* Q. Zeng, J. Wang, Q. Ma, H. Li,
H. Li,* G. Yang
&& – &&
Furazans with Azo Linkages: Stable
CHNO Energetic Materials with High
Densities, Highly Energetic
Performance, and Low Impact and
Friction Sensitivities
These compounds exhibit high densi-
ties, excellent detonation properties,
and relatively low impact and friction
sensitivities. These properties, together
with their high nitrogen contents, make
them potential candidates as mechani-
cally insensitive high explosives.
Chem. Eur. J. 2016, 22, 1 – 7
www.chemeurj.org
7
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ