Angewandte
Chemie
Explosives
From N-Nitro to N-Nitroamino: Preparation of High-Performance
Energetic Materials by Introducing Nitrogen-Containing Ions
Ping Yin and Jeanꢀne M. Shreeve*
Abstract: In the design of energetic materials, high energetic
performance and good molecular stability are two main goals.
Energetic functionalization which strives for maximum energy
often results in unstable chemical bonds and causes safety
problems in practical production and storage operations. In
this work, N-nitro- and N-nitroamino-functionalized mono-
and bis(1,2,4-triazoles) were synthesized and characterized by
infrared, and multinuclear NMR spectra, and elemental
analyses. The N-nitroamino-functionalization strategy was
employed for bis(imidazole), leading to high density com-
pound 14 (2.007 gcm at 100 K; 1.94 gcm at room temper-
ature) and energetic salt 15. While N-nitro-functionalized
products are thermally unstable and highly moisture sensitive,
N-nitroamino-functionalized energetic salts, which are com-
prised of additional nitrogen-containing ions, exhibit good
density, moderate to excellent structural stabilities, and high
performance.
energetic functionalities because of the favorable balance
between stability and performance. In comparison, nitro-
amino and azido functionalities tend to increase the density
and detonation properties; however, their molecular stabil-
ities associated with thermal behavior, and impact and friction
sensitivity are not competitive with their nitro-functionalized
[
8]
analogues.
Here, our synthetic interest focuses on the various nitro-
and nitroamino-functionalized mono and bis(1,2,4-triazoles)
(Scheme 1). In spite of the good calculated performance for 2
and 7, the high moisture sensitivity and low thermal stability
result in both being unstable when stored at room temper-
ature. Interestingly, the N-nitroamino-functionalized com-
pounds (4 and 10) are more stable thermally and the neat
compounds can be stored for an extended period. The ionic
derivatives of 4 and 10 show enhanced molecular stability and
excellent detonation properties. Compared to N-nitro-func-
tionalized compounds (2 and 7), further introduction of
nitrogen-containing ions acts as an energetic buffer to
stabilize greatly the nitrogen-rich frameworks, and retain
high energetic performance. Additionally, introduction of the
N-nitroamino functionality into bis(imidazoles) also gives rise
to new analogues 14 and 15 which have promising energetic
performance.
À3
À3
E
nergetic materials play a pivotal role in both military and
civilian fields, e.g., aerospace propellants, mining engineering,
and pyrotechnic technology. With increasingly variable ap-
plication demands for high energy density materials
(
HEDMs), energetic performance and molecular stability
[
1]
become two key criteria in evaluating overall properties. At
the molecular level, most typical HEDMs are composed of
organic frameworks and oxidizing moieties, such as 2,4,6-
N-Nitro- and N-nitroamino-functionalized monocyclic
1,2,4-triazoles (2–5) were prepared from 3-nitro-1H-1,2,4-
[
2]
[9]
trinitrotoluene (TNT)
and triaminotrinitro benzene
TATB). Heterocyclic chemistry supports the development
of energetic materials in the design of versatile nitrogen-rich
triazole (1). Since N,N’-dinitro-functionalized bi(1,2,4-tri-
[
3]
(
azole) (7) was highly unstable, our research interest was then
focused on N,N’-dinitroamino-functionalized bi(1,2,4-tri-
azole) (10). Employing modified amination conditions with
O-tosylhydroxylamine, 5,5’-dinitro-2H,2’H-3,3’-bi(1,2,4-tri-
azole)-2,2’-diamine (9) was prepared from the ammonium
salt, 8. (Scheme 2) Nitration of 9 occurred using mixed acid
(sulfuric acid and fuming nitric acid) and 10 was obtained by
filtration. Unlike the highly moisture-sensitive N,N’-dinitro
analogue 7, N,N’-dinitroamino-functionalized bi(1,2,4-tri-
azole), 10, exhibited unexpected hydrolytic stability. Reac-
tions of 10 with two equimolar amounts of nitrogen-rich bases
in ethanol or aqueous solution resulted in energetic salts
(11a–11 f) in nearly quantitative yields. To prepare the
triaminoguanidium salt (11g), an alternative synthesis was
used via a dipotassium intermediate, 12, with triaminoguani-
dium hydrochloride.
[
4]
backbones. In comparison with carbocyclic analogues,
heterocycle-based HEDMs feature high heats of formation,
and good thermal stability, as well as enhanced detonation
performance arising from tremendous energy storage in
[5]
nitrogen-rich backbones.
While nitrogen-rich heterocycles have become the core
motif in the search for new HEDMs, their compatibility with
other energetic functionalized groups is receiving increased
[
6]
attention. Diversified energetic functionalized groups, e.g.,
nitro, nitroamino, azido, azo, azoxy, trinitromethyl, and
trinitroethylamino groups are incorporated with nitrogen-
[
7]
rich backbones to tailor the energetic properties. Among
these, the nitro group is considered to be one of the superior
To examine the superiority of the N-nitroamino function-
ality, bis(imidazole) was chosen as a backbone to construct
new high-density heterocycles. The nitration reaction of
diamino compound 13 in mixed acid at low temperature
[
*] Dr. P. Yin, Prof. Dr. J. M. Shreeve
Department of Chemistry, University of Idaho
Moscow, ID 83844-2343 (USA)
E-mail: jshreeve@uidaho.edu
(
À15 to À108C) yielded 14 in excellent yield. The following
metathesis reactions with hydroxylammonium chloride gave
rise to dihydroxylammonium salt 15. The structures of the N-
Angew. Chem. Int. Ed. 2015, 54, 14513 –14517
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
14513