2,4,4,6,8,8-Hexanitro-2,6-diazaadamantane: A High-Energy Density Compound with High Stability

Article abstract of DOI:10.1021/acs.orglett.8b03107

A novel high-performance energetic compound of the polynitroazaadamantane family, 2,4,4,6,8,8-hexanitro-2,6-diazaadamantane, was designed and synthesized from 1,5-cyclooctadiene by two routes. Based on the experimental and calculated results, it exhibits a surprisingly high density (1.959 g cm^-3), high thermal stability (onset decomposition temperature of 235 °C), high positive heat of formation, and excellent detonation properties. These fascinating properties, which are comparable to those of CL-20, show great promise for potential applications as a high-energy density material.

Full text of DOI:10.1021/acs.orglett.8b03107

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
2,4,4,6,8,8-Hexanitro-2,6-diazaadamantane: A High-Energy Density
Compound with High Stability
Jian Zhang,‡ Tianjiao Hou,‡ Lin Zhang,* and Jun Luo*
School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
S
* Supporting Information
ABSTRACT: A novel high-performance energetic compound of the polynitroazaa-
damantane family, 2,4,4,6,8,8-hexanitro-2,6-diazaadamantane, was designed and
synthesized from 1,5-cyclooctadiene by two routes. Based on the experimental and
calculated results, it exhibits a surprisingly high density (1.959 g cm−3), high thermal
stability (onset decomposition temperature of 235 °C), high positive heat of
formation, and excellent detonation properties. These fascinating properties, which
are comparable to those of CL-20, show great promise for potential applications as a
high-energy density material.
Cage-like compounds such as cubane, isowurtzitane, and
ver the past decades, the development of new high-
Oenergy density materials (HEDMs) has attracted adamantane are very stable owing to their symmetrical and
significant interest.1 The desirable characteristics of these
rigid skeleton. The introduction of explosive groups onto their
frameworks can make them have the characteristics of high
energy, heat resistance, and insensitivity at the same time,
which might be one of the best candidates to solve the inherent
contradiction. Particularly, adamantane is an ideal fundamental
framework because of some attractive advantages: (1) excellent
stability owing to the diamand-like structure; (2) high inherent
density stemning from the ring tension and rigid structure; and
(3) good designability due to ten functionable sites. As a fact,
polynitroadamantanes have attracted widespread attention in
the field of energetic materials since the first reported 1,3,5,7-
tetranitroadamantane,15 which exhibits a moderate power
output but unbelievably high thermal stability (Tdec. > 360 °C)
and excellent impact stability.16 Until now, several polyni-
troadamantanes such as 1,2,2-trinitroadamantane,17 2,2,4,4-
tetranitroadamantane,18 2,2,6,6-tetranitroadamantane,19
2,2,4,4,6,6-hexanitroadamantane (HNA),20 and 4,4,8,8-tetrani-
troadamantane-2,6-diyl dinitrate21 have been synthesized.
Replacing the carbon atoms on the adamantane skeleton
with one or more nitramino groups will give the nitramine
derivatives higher density and energy while maintaining the
symmetry and good thermal stability.22 However, there are
only a few reports on the synthesis of polynitroazaadaman-
tanes. 3,5,7-Trinitro-1-azaadamantane was first synthesized as a
precursor of antitumor drugs by Theodor and co-workers in
1971.23 In the late 1990s, Nielsen and co-workers reported the
synthesis of 2,4,10-trinitro-2,4,10-triazaadamantane,24 a tem-
plate compound for the synthesis of 2,4,6,8,9,10-hexanitrohex-
aazaadamantane (HNHAA)25 that has not yet been synthe-
sized. In 2017, our group reported the synthesis of two
materials include high density, high detonation velocity and
pressure, good thermal stability, and low sensitivity toward
impact and friction.2 However, the discovery of high-energy
density compounds (HEDCs) is still an ongoing challenge due
to the inherent contradiction between detonation performance
and stability.3 In order to seek new HEDMs with an ideal
balance between performance and molecular stability, exten-
sive effort for synthetic and theoretical investigation has been
devoted, and a large amount of HEDCs have been reported.4
For example, N,N′-bis(trinitroethyl)-3,5′-dinitramino-4-(1,2,4-
triazol-3-yl)furazan,5 N-(2,3,5,6-tetranitro-4H,9H-dipyrazolo-
[1,5-a:5′,1′-d][1,3,5]triazin-4-yl)nitramide,6 3-nitramino-4-(5-
nitramino-1,2,4-triazol-3-yl)furazan,7 and 2,5-bis-
(trinitromethyl)-1,3,4-oxadiazole8 have been reported to be
powerful HEDCs with crystal densities of 1.932, 1.937, 1.920,
and 1.92 g cm−3, respectively. However, they still suffer from
the problems of poor thermal stability and sensitivity. On the
other hand, 5,5′-dinitro-3,3′-bis-1,2,4-triazole-2,2′-dinitro-
9
methyl (1.995 g cm−3
)
and dipotassium N,N′-(3,6-
dinitropyrazolo[4,3-c]pyrazole-1,4-diyl)dinitramidate (2.11 g
cm−3)10 are two examples of superhigh density HEDCs with
good thermal stability; however, they are extremely sensitive to
mechanical stimuli (shock and friction). In other cases, 5-(5-
amino-1H-1,2,4-triazole-3-yl)-1H-tetrazole,11 4-amino-3,5-bis-
(4-chloro-3,5-dinitro-pyrazol-1yl)methyl-1,2,4-triazole,12
5,5′,6,6′-tetranitro-2,2′-bibenzimidazole,13 and bis(4-amino-
3,5-dinitropyrazolyl)methane14 have excellent thermal stability
(Tdec. > 300 °C) but, unfortunately, exhibit poor density and
detonation performance. Therefore, the research focus of
HEDCs is still to seek an ideal balance between high
performance and acceptable molecular stability.
Received: September 29, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b03107
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
polynitroazaadamantanes, namely, 2,4,9-trinitro-2,4,9-triazaa-
damantane-7-yl nitrate26 and 2,4,4,8,8-petanitro-2-azaadaman-
tane.27 Four existing polynitroadamantanes or polynitroazaa-
damantanes with good explosive characteristics are depicted in
Figure 1. Based on the comparison of properties, we envisaged
designed two routes for the preparation of the key intermediate
4. One route would be realized from dione 5 by hydrazonation
and Bamford−Stevens elimination. Stoncius and co-workers
reported a method to synthesize the 2,6-oxygenated 9-
azabicyclo[3.3.1]nonanes by diepoxide 6,28 which could be
applied to synthesize dione 5. Finally, diepoxide 6 could be
achieved from 1,5-cyclooctadiene (8) by the reported method.
Alternatively, we presumed that the key precursor 4 could also
be prepared from 1,2,5,6-tetrabromocyclooctane (7) by
ammonolysis, elimination with liquid NH3, and nitrogen
acetylation.29 Similarly, compound 7 could also be synthesized
from 8 by the reported method.
As outlined in Scheme 1, the synthesis commenced with
5,10-dioxatricyclo[7.1.0.04,6]decane (6), prepared from 1,5-
Scheme 1. Synthesis of Diene 13 by Route 1
Figure 1. Chemical structures of several existing polynitroadaman-
tanes and polynitroazaadamantanes.
cyclooctadiene (8) by epoxidation reaction with oxone and
acetone in 79% yield.28 Compound 6 was then converted to 9-
azabicyclo[3.3.1]nonane-2,6-diol (9) through electrophilic
addition with saturated solution of ammonia in methanol.30
Treatment of 9 with Ac2O provided acetamide 10 in 45%
yield. The oxidation of the two hydroxyl groups was attempted.
To our disappointment, various oxidation methods such as
Swern oxidation, Jones oxidation, PCC oxidation, Colin
oxidation, DMP oxidation, and NaIO4/RuO2 oxidation were
attempted, but no target product 5 could be isolated. The low
lipid solubility of the raw materials might be the possible
reason.28,31 The acetyl group was therefore replaced with a
more soluable tert-butyloxycarbonyl (Boc) group. The reaction
of compound 9 with di-tert-butyl dicarbonate in methanol
under reflux afforded compound 11 in 94% yield. Stoncius and
co-workers synthesized the dione 12 by NaIO4/RuO2
oxidation in 80% yield. Different from the report, dione 12
was synthesized by Swern oxidation in 90% yield. Diene 13
was obtained in 70% yield via condensation of dione 12 with p-
toluenesulfonyl hydrazine followed by Bamford−Stevens
elimination with n-BuLi.
that the replacement of 6-carbon in 2,4,4,8,8-pentanitro-2-
azaadamantane with nitramino functionality to construct a
more symmetrical structure with more azo atoms and nitro
groups must give the analogue with observably higher
detonation performance and better stability.
In this paper, the synthesis and thermostability of the
designed molecule 2,4,4,6,8,8-hexanitro-2,6-diazaadmanatane
were investigated. The calculating detonation performance was
compared to some typical energetic compounds with excellent
performance.
The retrosynthetic analysis for 2,4,4,6,8,8-hexanitro-2,6-
diazaadamantane (1) is summarized in Figure 2. The target
Alternatively, according to the work reported by Nelsen and
co-workers,29 another route to synthesize diene 13 was
attempted (Scheme 2).
First of all, 1,2,5,6-tetrabromocyclooctane (7) was prepared
in 60% yield from 1,5-cyclooctadiene (8) by electrophilic
addition with bromine. Subsequently, it was converted to 9-
azabicyclo[3.3.1]nona-3,7-diene (14) by ammonolysis and
elimination with excess NH3 in a steel hydrogenation bomb.
Figure 2. Retrosynthetic analysis of 1.
Scheme 2. Synthesis of Diene 13 by Route 2
product could be obtained by nitration of the acetamide and
oxidative nitration of the ketoxime derived from the precursor
2. We envisioned that dione 2 might be obtained by nitrogen
acetylation and hydroxyl oxidation from the corresponding diol
3. Compound 3 could be achieved from diene 4 by
epoxidation and electrophilic addition with ammonia. We
B
DOI: 10.1021/acs.orglett.8b03107
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After the protection of secondary amine with (Boc)2O, diene
13 was achieved smoothly in 19% yield for two steps.
As a result, the two routes were both successful. The former
route has the advantages of higher yield (39.7%) for over 6
steps and relatively convenient experimental operation.
Although the total yield of the latter route was just 11.4%
and autoclave condition was needed, it was realized through a
much shorter route (only 3 steps), which is more suitable for
rapid and scaled-up preparation of diene 13.
With diene 13 in hand, the stage was set for the construction
of the diazaadamantane skeleton (Scheme 3). Following a
Scheme 3. Synthesis of 1
Figure 3. X-ray crystal structure of 1 (ellipsoid view).
similar synthetic strategy as shown in route 1, diepoxide 15 was
obtained in 65% yield by epoxidation with mCPBA. After
electrophilic addition with a saturated solution of ammonia in
methanol, the skeleton of 2,6-diazaadamantane was success-
fully constructed. Taking the subsequent oxidation of the diol
into account, the secondary amine was still protected with
(Boc)2O to afford 16 in 86% yield for two steps. To our
delight, 16 was then smoothly oxidated by Dess-Martin
periodinane to produce the corresponding dione 17 in 85%
yield. In addition, some other oxidation methods such as
Swern oxidation, TEMPO/NaClO oxidation, and NaIO4/
RuO2 oxidation were applied, and the target product could also
be isolated with much lower yields (20%∼40%). The direct
nitrolysis of N-Boc was found to be a failure. Referring to our
established synthetic strategy for 2,4,4,8,8-pentanitro-2-azaa-
damantane, the deprotection of N-Boc was furnished in TFA/
CH2Cl2 at room temperature. The derived secondary amine
was treated with Ac2O to afford the acetamide 2. Subsequently,
treatment of 2 with hydroxylamine hydrochloride in methanol
gave the corresponding dioxime derivative. After oxidative
nitration of dioxime with N2O5 in reflux CH2Cl2, the gem-
dinitro product 18 was obtained (18% over 4 steps). Finally,
the nitrolysis of N-Ac in HNO3/oleum (20%) at 80 °C for 16
h delivered the target product 2,4,4,6,8,8-hexanitro-2,6-
diazaadamantane (1) in 82% yield. The crystal structure of
compound 1 was depicted in Figure 3.
Figure 4. TG-DSC curves of 1.
Gaussian 09 suite of programs.32 DFT with the B3LYP33
functional and 6-31G* basis set34 was used to optimize the
structure. The detonation velocity, detonation pressure, and
heat of formation were estimated by the Kamlet−Jacobs
formula.35 By comparing physicochemical properties of 1 and
2,4,4,8,8-petanitro-2-azaadamantane (Table 1), we found that
Table 1. Physical Properties of Compound 1 and Some
Typical Energetic Compounds
a
b
c
d
e
d
ΔHf
D
P
Tdec
compound (g·cm−3
)
(kJ·mol−1
)
(m·s−1
)
(GPa)
(°C)
1
RDX
β-HMX
ε-CL-20
1.959
169.9
86.3
116.1
365.4
9310
8983
9221
9455
40.3
34.9
39.2
45.2
235
210
279
215
1.80636
1.90437
2.03538
a
b
e
Density determined from single-crystal X-ray diffraction analysis.
Heat of formation. Detonation velocity. Detonation pressure.
Decomposition temperature (onset).
c
d
the symmetrical introduction of one nitroamino functionality
to replace the 6-carbon can greatly improve the density,
thermal stability, and detonation properties, which proved the
validity of our original hypothesis. These fascinating properties,
which are comparable to those of CL-20,39 show great promise
for potential applications as a high-energy density material.
In conclusion, a novel high-density energetic compound,
2,4,4,6,8,8-hexanitro-2,6-diazaadamantane, has been designed
and successfully synthesized from 1,5-cyclooctadiene by two
routes. Its crystal density was determined to be 1.959 g cm−3,
The thermal stability of 1 was determined by differential
scanning calorimetry (DSC) and thermogravimetry (TG). The
onset decomposition temperature was found to be 235 °C, and
the exothermic peak at 276 °C accounts for a rapid
decomposition (Figure 4). In short, compound 1 possesses
satisfactory thermal stability.
The physicochemical properties of 1, including the thermal
and detonation properties, were calculated by using the
C
DOI: 10.1021/acs.orglett.8b03107
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
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ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b03107.
(10) Yin, P.; Zhang, J.-H.; Mitchell, L. A.; Parrish, D. A.; Shreeve, J.
M. Angew. Chem., Int. Ed. 2016, 55, 12895−12897.
(11) Dippold, A. A.; Klapotke, T. M. Chem. - Asian J. 2013, 8, 1463−
1471.
Detailed experimental procedures and characterization
data (PDF)
(12) Tang, Y.-X.; Gao, H.-X.; Parrish, D. A.; Shreeve, J. M. Chem. -
Eur. J. 2015, 21, 11401−11407.
Accession Codes
(13) Gutowski, L.; Trzcinski, W.; Szala, M. ChemPlusChem 2018, 83,
87−91.
CCDC 1854396 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
Corresponding Authors
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*E-mail: zhangl@njust.edu.cn.
*E-mail: luojun@njust.edu.cn.
ORCID
Lin Zhang: 0000-0002-4193-8877
Jun Luo: 0000-0002-8093-5345
Author Contributions
‡Jian Zhang and Tianjiao Hou contributed equally.
Notes
(24) Nielsen, A. T.; Chafin, A. P.; Christian, S. L.; Moore, D. W.;
Nadler, M. P.; Nissan, R. A.; Vanderah, D. J.; Gilardi, R. D.; George,
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was sponsored by the Qing Lan Project of Jiangsu
Province, P. R. China. The authors are grateful to Dr. Yue
Zhao from Nanjing University for the single-crystal structure
analysis.
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