Synthesis of thermally stable energetic 1,2,3-triazole derivatives

Article abstract of DOI:10.1002/chem.201203192

Various thermally stable energetic polynitro-aryl-1,2,3-triazoles have been synthesized through Cu-catalyzed [3+2] cycloaddition reactions between their corresponding azides and alkynes, followed by nitration. These compounds were characterized by analyti

Full text of DOI:10.1002/chem.201203192

FULL PAPER
DOI: 10.1002/chem.201203192
Synthesis of Thermally Stable Energetic 1,2,3-Triazole Derivatives
A. Sudheer Kumar,[a] Vikas D. Ghule,[a] S. Subrahmanyam,[a] and Akhila K. Sahoo*[a, b]
Abstract: Various thermally stable en-
ergetic polynitro-aryl-1,2,3-triazoles
techniques. Most of the polynitro-bear-
ing triazole derivatives decomposed
within the range 142–3198C and their
heats of formation and crystal densities
were determined from computational
studies. By using the Kamlet–Jacobs
empirical relation, their detonation ve-
locities and pressures were calculated
from their heats of formation and crys-
tal densities. Most of these newly syn-
thesized compounds exhibited high
positive heats of formation, good ther-
mal stabilities, reasonable densities,
and acceptable detonation properties
that were comparable to those of TNT.
have been synthesized through Cu-cat-
alyzed [3+2] cycloaddition reactions
between their corresponding azides
and alkynes, followed by nitration.
These compounds were characterized
by analytical and spectroscopic meth-
ods and the solid-state structures of
most of these compounds have been
determined by using X-ray diffraction
Keywords: copper · cycloaddition ·
energetic materials · heats of for-
mation · triazoles
Introduction
performance explosives because they possess high positive
ꢀ
ꢀ
heats of formation, owing to their N N and C N bonds and
Formidable challenges remain in the development of less
sensitive and thermally stable energetic materials because
this process requires a detailed investigation into the design
of N- and O-rich molecules, the determination of their
energy content through computational studies, as well as the
demonstration of reliable strategies for their synthesis.[1]
Therefore, the synthesis of small organic molecular frame-
works that have high N- and O-content as thermally stable
energetic materials from readily available precursors is
always desirable.[2] In general, the presence of benzene moi-
eties in the form of energetic polynitroarenes lowers the hy-
groscopic nature of a material, as well as its synthetic cost;
this group also decreases the sensitivity of the material to
impact, shock, and friction.[3] Five-membered azole hetero-
cycles behave as a source of energy owing to their high N
content.[4] Therefore, nitrogen-rich aromatic-triazole-based
energetic materials have invariably been used in civil and
military applications, such as in aerospace propellants,
smoke-free pyrotechnic fuels, fire extinguishers, and so
on.[5,1g] In essence, 1,2,3-triazoles are considered to be one
of the most promising backbones for the fabrication of high-
ring strain.[6,1g] In addition, the aromatic nature of the tri-
AHCTUNGTREGaNNNU zole moiety makes the molecule thermally stable. Unfortu-
nately, most of the better-performing energetic materials are
practically unsuitable for safe handling, whereas materials
with lower sensitivity do not show good-enough perform-
ance with respect to the benchmark explosives.[7] Apart
from a high positive heat of formation, a high oxygen bal-
ance and high density improve the detonation performance
of a material and make the molecule a better-performing
energetic material. In general, the incorporation of nitro
groups into a molecular backbone enhances the oxygen bal-
ance and density.[8]
Herein, we report the synthesis of various N-benzyl-/aryl-
and/or pyridyl-tethered 1,2,3-triazoles by using the known
Cu-catalyzed [3+2] cycloaddition reaction between their
corresponding azides and terminal alkynes. Nitration on
these precursors delivered a wide range of nitro-rich 1,2,3-
triazole derivatives as thermally stable energetic materials.
The solid-state structures of most of these newly synthesized
compounds were elucidated by using X-ray diffraction tech-
niques.
Results and Discussion
[a] A. S. Kumar, V. D. Ghule, S. Subrahmanyam, Prof. Dr. A. K. Sahoo
Advanced Center of Research in High Energy Materials
University of Hyderabad, Hyderabad-500046 (India)
The development of simple and efficient approaches for the
creation of triazole skeletons in small molecular entities has
always attracted considerable attention.[9] Importantly, the
Cu-catalyzed [3+2] cycloaddition reaction between an azide
and an alkyne, termed the “click reaction”, is a reliable syn-
thetic strategy for the efficient formation of 1,2,3-triazole
skeletons in high yields with affordable cost and high regio-
selectivity.[10] Herein, we report the synthesis of nitro-rich
[b] Prof. Dr. A. K. Sahoo
School of Chemistry, University of Hyderabad
Hyderabad 500046 (India)
E-mail: akhilchemistry12@gmail.com
akssc@uohyd.ernet.in
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203192.
Chem. Eur. J. 2013, 19, 509 – 518
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509

benzyl-/aryl- and pyridyl-tethered 1,2,3-triazoles as new ther-
mally stable energetic materials.
responding products, 3e–3g, in good-to-excellent yields
(Table 1, entries 5–7).
In general, electron-rich azides (dipoles) and electron-
poor alkynes (dipolarophiles) favor the cycloaddition reac-
tion, whereas steric bulk on the acetylene retards the rate of
the reaction.[11] It has been reported that the cycloaddition
reaction of electron-rich dipolarophiles proceeds well in
water and in protic solvents.[12] The base-mediated deprotec-
With a series of triACTHNGUTERNNUaG zole-based molecules in hand, the ni-
trations of compounds 3a–3g were independently per-
formed in either a mixture of 70% HNO3 and 98% H2SO4
(Conditions A) or 95% HNO3 and 98% H2SO4 (Condi-
tions B), as shown in Equation (1). Table 2 summarizes the
nitration reactions of the N-benzyl-substituted-1,2,3-triazoles
(3). At first, compound 3a was heated under conditions A
at 1208C for 24 h. Nitro-rich regioisomeric products 5a–8a
were detected and purified easily by column chromatogra-
phy on silica gel in an overall 83% yield (Table 2, entry 1).
In non-polar trinitro-bearing compound 5a, which was iso-
lated in 15% yield, the two nitro groups were substituted at
the o- and p-positions on the N-benzyl ring, whilst the other
nitro group was inserted at the 4-position of the triazole
moiety. As expected, the o,p-dinitro-substituted compound
6a was isolated in 39% yield as the major product. Interest-
ingly, the m,m- and m,p-dinitro substituted compounds 7a
and 8a, respectively, were also isolated, albeit in poor yields.
The factors that were responsible to the formation of these
unlikely meta-substituted products (7a and 8a) remain un-
clear. The introduction of more nitro groups onto the molec-
ular framework usually enhances the density and detonation
properties of a compound. Therefore, we speculate that the
use of 95% HNO3 in the nitration reactions could influence
the formation of the tetranitro substituted products. There-
fore, the nitration of compound 3a was carried out under
conditions B at 1008C. Although compound 3a was com-
pletely consumed within 12 h, products 5a–8a were exclu-
sively formed (Table 2, entry 1), as observed previously.
ꢀ
tion of the C Si bond occurs smoothly in protic solvent at
ambient temperature.[13] With these facts in mind, the cyclo-
addition reactions between readily accessible benzyl azides
and electron-rich TMS-acetylene (1) were carried out under
the previously reported conditions involving sodium ascor-
bate, CuSO4, and K2CO3 as a base in MeOH/water at room
temperature for 24 h (Table 1).[14] Benzyl azides were pre-
Table 1. CuI-catalyzed 1,3-dipolar cycloaddition of benzyl azides and
TMS-acetylene (1).[a]
Entry
2
R
Base
Yield [%][b]
3
4
1
2
3
4
5
6
7
2a
2b
2c
2d
2e
2 f
2g
H
K2CO3
K2CO3
KOAc
K2CO3
K2CO3
K2CO3
K2CO3
92
87
83
53
92
79
52
3
0
9
0
0
0
0
4-NO2
3-NO2
2-NO2
4-OMe
3-OMe
2-OMe
[a] All reactions were carried out with azide (1.0 equiv), TMS-acetylene
(1.5 equiv), base (potassium carbonate or potassium acetate, 1.2 equiv),
sodium ascorbate (0.4 equiv), and CuSO4·5H2O (0.2 equiv) in a mixture
of MeOH/water (1:1, 0.5 mL for 1 mmol) at room temperature for 24 h.
[b] Yield of isolated product.
pared from the commercially available benzyl bromides by
nucleophilic displacement with NaN3 in DMSO in almost
quantitative yields.[15] The electronically neutral benzyl azide
2a reacted smoothly with 1 to give compound 3a in 92%
Next, the nitration reactions of nitro-substituted triazoles
3b–3d were independently conducted under conditions A
and B. The products, 5a (12%), 6a (70%), and 8a (11%),
were obtained from 3b under conditions A at 1208C, where-
as the same reaction under conditions B at 708C gave com-
pounds 6a and 8a in good overall yields (Table 2, entry 2).
Similarly, the nitrations of compound 3c under conditions A
or B delivered 7a and 8a as the major and minor products,
respectively (Table 2, entry 3). Compound 6a was exclusive-
ly obtained from the nitration of o-nitro-substituted triazole
3d under both sets of conditions (Table 2, entry 4). Thus,
variously substituted nitro-containing products (6a, 7a, and
8a) can be directly prepared from 3 in good yields. In gener-
al, electron-rich aromatic compounds undergo electrophilic-
substitution reactions with ease. Therefore, we anticipated
that the OMe group on the aryl moiety in benzyl triazoles
would facilitate the introduction of more nitro groups onto
the aromatic skeleton. Thus, the nitration of 4-OMe-susbti-
yield; the corresponding TMS-substituted 1,2,3-triACTHNUGTRNEUNGazole 4a
was also isolated in trace amounts (Table 1, entry 1). An ac-
tivated aryl azide that had a nitro group at the 4-position on
the phenyl ring underwent cycloaddition with 1, thereby
producing compound 3b in 87% yield (Table 1, entry 2). A
poor yield of compound 3c was obtained when the reaction
of 3-nitrobenzyl azide (2c) with 1 was conducted under the
optimized conditions. Interestingly, KOAc was found to be
suitable as the base and the desired compound, 3c, was iso-
lated in 83% yield (Table 1, entry 3). Sterically demanding
2-nitro-substituted benzyl azide 2d reacted poorly with com-
pound 1 and only afforded compound 3d in moderate yield,
with a fair amount of recovered unreacted compound 2d. A
similar trend of reactivity and selectivity was observed in
the reactions of MeO-substituted benzyl azides 2e–2g with
1 under the optimized conditions, thus delivering their cor-
510
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Chem. Eur. J. 2013, 19, 509 – 518

Thermally Stable Energetic 1,2,3-Triazole Derivatives
FULL PAPER
Table 2. Nitration reactions of triazoles 3.
Entry
3
T [8C]
t [h]
Polynitro derivatives of benzyl-1,2,3-triazoles[c]
5a
15
14
12
–
–
–
–
–
6a
39
35
70
64
–
–
88
93
7a
20
25
–
8a
9
1
2
3
4
3a
3b
3c
3d
120[a]
100[b]
120[a]
70[b]
80[a]
24[a]
12[b]
24[a]
6[b]
10
11
13
25
30
–
–
12[a]
10[b]
8[a]
60
62
–
60[b]
60[a]
45[b]
6[b]
–
–
5
6
3e
3 f
RT[a]
2[a]
–
–
–
–
RT[b]
RT[a]
RT[b]
2[b]
2[a]
2[b]
–
–
–
9 (71[a], 76[b]
)
–
–
–
–
–
10 (75[a], 81[b]
)
7
3g
RT[a]
6[a]
–
–
–
–
RT[b]
2[b]
–
–
11 (48[a], 64[b]
)
[a] Mixture of 70% HNO3 and 98% H2SO4. [b] Mixture of 95% HNO3 and 98% H2SO4. [c] Yield of isolated product.
tuted triazole 3e was independently carried out under con-
ditions A and B; the di-ortho-nitro-substituted product 9
was exclusively isolated in good yield (Table 2, entry 5).
Gratifyingly, the trinitration product, 10, was obtained in
81% yield when m-methoxy-bearing triazole 3 f was ex-
posed to conditions B at RT for 2 h (Table 2, entry 6). On
the other hand, the sterically demanding compound 3g de-
livered the o,p-dinitration product (11) as a thick liquid in
moderate yield (Table 2, entry 7). These results reveal that
conditions B are more mild than conditions A. In addition,
more reactive and highly productive nitration reactions are
observed under conditions B in comparison to conditions A.
X-ray diffraction analysis confirmed the structures of com-
pounds 5a, 6a, 7a, 8a, and 9, as depicted in Figure 1.
Next, we turned our attention to exploring the nitration
reactions of aryl-1,2,3-triazoles and the synthesis of various
polynitroaryl triazoles. We anticipate that these nitro-con-
taining N-aryl triazoles would show better energetic proper-
Figure 1. Molecular structures of compounds 5a, 6a, 7a, 8a, 9, 20, 21, 22, and 25a; thermal ellipsoids are set at 30% probability and hydrogen atoms are
unlabeled for clarity.
Chem. Eur. J. 2013, 19, 509 – 518
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511

A. K. Sahoo et al.
Table 4. Nitration reactions of compounds 13.[a]
ties compared to their corresponding nitro-substituted N-
benzyl triazoles, because of their lower carbon content. In
addition, the presence of the triazole skeleton on the aryl
ꢀ
ring (C N bond) would facilitate the electrophilic-nitration
process.
Entry 13
T [8C] t [h] Nitro derivatives of phenyl-1,2,3-triazoles[b]
The Cu-catalyzed cycloaddition reaction between an aryl
azide and TMS-acetylene (1) is a reliable method for the
synthesis of aryl triACHTUNGTRENNUNG
azoles (Table 3).[14] Aryl azides are easily
1
13a 100
24
15 (5)
17 (18)
19 (85)
16 (25)
18 (16)
Table 3.
ACHTUNGTRENNUNG[3+2] Cycloaddition reactions between aryl azides and TMS-
acetylene.[a]
2
13c 160
24
Entry
12
R
Base
Yield [%][b]
3
4
5
13e RT
2
13
14
1
2
3
4
5
6
7
12a
12b
12c
12d
12e
12 f
12g
H
K2CO3
K2CO3
K2CO3
KOAc
K2CO3
K2CO3
KOAc
66
45
73
30
85
79
41
0
0
0
59
0
0
4-NO2
3-NO2
2-NO2
4-OMe
3-OMe
2-OMe
13 f RT
2
2
29
[a] All reactions were carried out with azide (1.0 equiv), TMS-acetylene
(1.5 equiv), base (potassium carbonate or potassium acetate, 1.2 equiv),
sodium ascorbate (0.4 equiv), and CuSO4·5H2O (0.2 equiv) in a mixture
of MeOH/water (1:1, 0.5 mL for 1 mmol) at room temperature for 24 h.
[b] Yield of isolated product.
20 (33)
22 (82)
21 (46)
13g RT
accessible in good yields from their corresponding commer-
cially available aryl amines, through diazotization followed
by azide substitution.[15] The reaction between phenyl azide
(12a) and 1 was successfully conducted under previously op-
timized conditions (sodium ascorbate, CuSO4, and K2CO3 as
a base in MeOH/water at room temperature) and the prod-
uct 13a was isolated in 66% yield (Table 3, entry 1). p/m-
[a] Mixture of 95% HNO3 and 98% H2SO4. [b] Yield of isolated product
is shown in parenthesis.
tained in poor yields when compound 13c was reacted
under conditions B at 1608C (Table 4, entry 2). Unfortunate-
ꢀ
ly, cleavage of the C N linkage of the aryl triazole was ob-
Nitro/meth
G
served when the reaction was conducted in strong acids at
higher temperatures.[16] The presence of a nitro group at the
ortho/para position with respect to the triazole made the
aryl ring highly electron deficient and, therefore, compounds
13b and 13d failed to undergo nitration under both sets of
conditions, even when the reaction was performed at elevat-
ed temperatures. Therefore, we investigated the nitration re-
actions of electron-rich methoxy-substituted aryl triazoles.
Owing to the o- and p-directing nature of the OMe group,
nitration of 4-MeO-substituted phenyl triazole 13e exclu-
sively produced the di-ortho-nitro-containing product 19 in
85% yield under conditions B at room temperature
(Table 4, entry 3). A regioisomeric mixture of o,p-dinitro-
substituted products 20 and 21 was obtained from the nitra-
tion of 3-OMe-substituted triazole 13 f in good overall yield
(Table 4, entry 4). The sterically encumbered compound 13g
delivered 22 in 82% yield when the reaction was carried out
under conditions B at room temperature for 2 h. Unfortu-
nately, our efforts to achieve the tri- and/or tetranitro-substi-
cycloaddition with 1, thereby delivering triazoles 13b,c and
13e,f in good to excellent yields (Table 3, entries 2–3 and 5–
6). However, the cycloaddition reactions of ortho-substituted
aryl azides 12d and 12g were successfully performed in the
presence of KOAc as the base: their corresponding 1-substi-
tuted-1,2,3-triazoles 13d and 13g were isolated in moderate
yields and TMS-bearing 1,4-disubstituted-triazoles 14d and
14g were also formed in fairly good amounts (Table 3, en-
tries 4 and 7). The desilylation of compounds 14d and 14g
with K2CO3 in MeOH readily gave their corresponding
products 13d and 13g.[13]
The nitration of N-aryl-substituted 1,2,3-triazoles was in-
dependently examined under conditions A and B (Table 4).
Our attempts to nitrate compound 13a under conditions A
were unsuccessful; however, heating compound 13a at
reflux under conditions B gave mono-nitro derivatives 15
and 16 in poor yields (Table 4, entry 1). The m,p-dinitro-sub-
stituted product (17) and trinitro benzene (18) were ob-
512
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Thermally Stable Energetic 1,2,3-Triazole Derivatives
FULL PAPER
Table 6. Synthesis of pyridine-N-oxides 25a and 25b.
tuted aryl triazole were futile. The structures of compounds
20, 21, and 22 were confirmed by single-crystal X-ray analy-
sis (Figure 1).
Heat of formation (HOF) is a valuable factor that deter-
mines the nature and efficiency of highly energetic materi-
als.[6] Our synthesized polynitro-1,2,3-triazole derivatives
(5a–11 and 15–22) all showed positive HOFs that varied
from 197–401 kJmolꢀ1. These results reveal that the 1,2,3-tri-
azole skeleton is beneficial to a positive HOF value. There-
fore, we believe that the incorporation of more triazole
rings would enhance the heat of formation of the molecule.
The fact that a pyridine moiety contributes more energy
than a benzene ring is well-established.[17] Based on this in-
formation, new molecular entities 24, in which two triazole
skeletons are attached onto a pyridine template, were pro-
posed and their synthesis was initiated through a cycloaddi-
tion reaction between 2,6-bis(azidomethyl)-pyridine (23)
and the corresponding alkynes (Table 5). The precursor 23
Entry 24
R
H
T [8C] t [h] 25
R1
H
Yield [%][a]
35
1[b]
2
24a
70
48
24
25a
24b H2COCOEt RT
25b H2CNO2 41
[a] Yield of isolated product. [b] Nitration failed, even at high tempera-
ture.
conditions B at room temperature. Subsequently, the puri-
fied nitro-containing product was reacted with mCPBA at
room temperature and the desired N-oxide product 25b was
isolated in 41% yield over two steps (Table 6, entry 2).
Table 5. Synthesis of bis-1,2,3-triazoles from their corresponding azides
and alkynes.[a]
X-ray crystallography: Single crystals were grown by the
slow evaporation of solutions of 5a, 6a, 7a, 8a, 9, 20, 21, 22,
and 25a in EtOAc at room temperature and atmospheric
pressure. The structures of 5a, 6a, 7a, 8a, 9, 20, 21, 22, and
25a were unambiguously elucidated by single-crystal X-ray
diffraction analysis. The molecular structures of 5a, 6a, 7a,
8a, 9, 20, 21, 22, and 25a are shown in Figure 1. Compounds
5a, 7a, 8a, 9, 20, and 25a crystallized in monoclinic space
groups P21, P21/n, P21/c, P21/n, P21/c, and C2/c, with cell vol-
umes of 557.09(10), 1016.72(14), 1074.68(14), 1240.45(14),
2316.6(6), and 1182.7(4) ꢁ3, respectively, whereas 6a, 21,
and 22 crystallized in the orthorhombic space group P212121
with cell volumes of 1075.07(12), 1112.8(8), 1141(4) ꢁ3, re-
spectively. The crystallographic data of all of these com-
pounds are detailed in Table 7.
Entry
23
R
Base
24
Yield [%][b]
1
2
23a
23b
TMS (1)
H2COCOEt (1’)
K2CO3
KOAc
24a
24b
74
88
[a] All reactions were carried out with azide (1.0 equiv), TMS-acetylene
(3.0 equiv), base (potassium carbonate or potassium acetate, 2.4 equiv),
sodium ascorbate (0.8 equiv), and CuSO4·5H2O (0.4 equiv) in a mixture
of MeOH/water (1:1, 1 mL for 1 mmol) at room temperature for 24 h.
[b] Yield of isolated product.
This work demonstrates the synthesis of polynitrobenzyl-
(5a–11), polynitro-N-aryl- (15–22), and polynitropyridyl-
containing triazoles (25a and 25b). Essential parameters,
such as heat of formation (HOF), density (1), detonation ve-
locity (D), and detonation pressure (P), determine the
nature and efficiency of energetic materials. Table 8 summa-
rizes the energetic properties of these materials. The HOF is
indicative of the energy content of high-energy materials;
the newly synthesized triazole derivatives showed positive
HOFs, that is, in the range 197–683 kJmolꢀ1. Of the benzyl-
substituted triazole derivatives, compound 5a possessed the
highest HOF (390.3 kJmolꢀ1), owing to the presence of
three nitro groups in the molecular backbone. Compound
5a showed better density and performance than the other
nitro-bearing benzyl derivatives 6a–8a and 9–11, because it
contained one more nitro group than the latter compounds.
Changes in the positions of the nitro groups in the molecu-
lar structure did not affect the HOF values, as observed in
compounds 6a, 7a, and 8a. Similar trends were observed in
polynitro-N-aryl-triazole derivatives 19–22. Of the triazole
derivatives, pyridyl-based compound 25a showed the higher
HOF, which can be attributed to the presence of triazole
was obtained from the commercially available 2,6-
bis(bromoACHTUNGTRENNUNGmethACHTUNGTRENNUNGyl)pyridine by the nucleophilic displacement
of bromide by NaN3 in good yield.[18] The cycloaddition of
compound 23 to TMS-acetylene (1) under the optimized
conditions gave 24a in 74% yield at room temperature
(Table 5, entry 1). Similarly, the reaction between compound
23 and propargyl propionate (1’) in the presence of KOAc
afforded 24b in excellent yield (Table 5, entry 2).
Our efforts to nitrate compound 24a failed, even when
the reaction was performed at high temperatures under con-
ditions A and B. Presumably, the protonation of the pyri-
dine-N atom by the acids hindered the electrophilic nitra-
tion of the pyridine moiety. However, the oxidation of com-
pound 24a with mCPBA in CHCl3 at 708C delivered the
corresponding N-oxide product 25a in 35% yield (Table 6,
entry 1). X-ray diffraction studies establish the structure of
25a (Figure 1).
A recent report by Shreeve and co-workers[19] inspired us
to introduce more nitro groups onto the methylene hydro-
gen atoms of compound 24b. However, we noted the forma-
tion of the mono-nitro derivative of compound 24b under
Chem. Eur. J. 2013, 19, 509 – 518
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513

A. K. Sahoo et al.
Table 7. Crystallographic data for compounds 5a, 6a, 7a, 8a, 9, 20, 21, 22, and 25a.
Compound
5a
6a
7a
8a
9
20
21
22
25a
CCDC
formula
Mw
895107
C9H5N6O6
293.19
895108
C9H7N5O4
249.20
895109
C9H7N5O4
249.20
895110
C9H7N5O4
249.20
896656
C10H9N5O5
279.22
895111
C9H7N5O5
265.20
895112
C9H7N5O5
265.20
895113
C9H7N5O5
265.20
895114
C11H11N7O1
257.27
crystal system monoclinic orthorhombic monoclinic monoclinic monoclinic
monoclinic orthorhombic orthorhombic monoclinic
space group
T [K]
a [ꢁ]
b [ꢁ]
c [ꢁ]
a [8]
P21
100
P212121
298
5.5436(4)
11.9190(8)
P21/n
100
10.0567(8)
9.2416(7)
10.9434(9)
90
P21/c
293
8.6097(7)
11.3982(8)
11.0544(7)
90
P21/n
P21/c
298
P212121
298
P212121
298
5.554(3)
12.461(6)
16.49(6)
90
C2/c
298
14.179(3)
7.7450(17)
10.792(2)
90
293 K
11.6392(8)
5.4843(3)
19.6637(14)
90
5.5245(6)
5.5719(6)
18.1323(19) 16.2706(10)
10.8498(16) 5.6454(18)
12.1869(18) 13.486(7)
18.249(3)
90
14.616(5)
90
90
90
b [8]
g [8]
93.521(2)
90
2
557.09(10)
1.748
0.151
5787
90
90
4
91.5180(10) 97.843(7)
98.790(7)
90
4
106.253(2)
90
8
2316.6(6)
1.521
0.127
20797
3933
90
90
4
1112.8(8)
1.583
0.132
3131
2095
1545
90
90
4
1141(4)
1.544
0.129
2165
1451
1264
93.667 (4)
90
4
1182.7(4)
1.445
0.102
5768
90
4
90
4
Z
V [ꢁ3]
1075.07(12)
1.540
1.077
3071
1851
1700
1016.72(14) 1074.68(14) 1240.45(14)
Dcalc [gcmꢀ3
]
1.628
0.132
8988
1763
1603
1.540
0.125
4709
2408
1687
1.495
0.123
3255
2811
1688
m [mmꢀ1
total reflns
]
unique reflns 2177
observed
reflns
1137
901
2098
3303
R
G
0.0355
0.0879
1.114
0.0381
0.0982
1.073
0.0350
0.0806
1.088
0.0450
0.1282
0.863
0.0733
0.2306
1.241
0.0682
0.1823
1.122
0.0366
0.0835
0.968
0.0889
0.2440
1.082
0.0504
0.1245
1.126
wR2 [all]
GOF
diffractometer SMART
Xcalibur
Gemini Eos
CCD
SMART
APEX
CCD
SMART
APEX
CCD
Xcalibur
Gemini Eos
CCD
SMART
APEX
CCD
Xcalibur
Gemini Eos
CCD
Xcalibur
Gemini Eos
CCD
Xcalibur
Gemini Eos
CCD
APEX
CCD
Table 8. Energetic properties of the 1,2,3-triazole derivatives.
dine–triazole molecules 25a and 25b possess higher
HOFs.[17] Density is a primary physical parameter that deter-
mines the detonation performance of a molecule. The deto-
nation velocity increases with packing density and the deto-
nation pressure varies proportionally with respect to the
square of the density. The densities of the triazole deriva-
tives were in the range 1.38–1.64 gcmꢀ3. As evident in
Table 8, the predicted densities (from their cvff force fields)
closely matched their observed crystal densities. The incor-
poration of nitro groups into a framework improves its den-
sity. As a consequence, a noticeable variation in density was
clearly visible between compounds 16 and 17; a similar
trend was observed among compounds 5a and 6a, 9 and 10,
and 25a and 25b. The velocity of detonation (D) is a func-
tion of the energy that is produced by explosive decomposi-
tion. The density, heat of formation, and atomic composition
can be integrated into an empirical formula to predict the
performance of a proposed explosive. The detonation veloci-
ty and detonation pressure of the triazole derivatives were
computed by Kamlet–Jacobs empirical equations and the re-
sults are shown in Table 8. Detonation performance mainly
depends on the crystal density, whereas, the contribution of
the HOF to the detonation properties is negligible. For ex-
ample, compounds 25a and 25b show poor detonation per-
formance, apart from their high HOFs. Of the synthesized
triazole derivatives, compound 5a demonstrated the best
performance, owing to its high crystal density. Thus, com-
pound 5a possessed D=6.99kmsꢀ1 and Pꢁ20.07 GPa. The
thermal stabilities of the triazole derivatives were deter-
mined by DSC-TGA measurements. The triazole derivatives
decomposed in the range 142–3198C. Interestingly, com-
[f]
Compound OB[a]
[%]
1[b]
[gcmꢀ3
D[c]
[kmsꢀ1
P[d]
A
M.p.[e] Td
HOF[g]
[kJmolꢀ1
]
G
]
E
]
[oC]
G
5a
6a
7a
8a
9
ꢀ81.6 1.64
(1.75)
ꢀ112.4 1.53
(1.54)
ꢀ112.4 1.53
(1.63)
ꢀ112.4 1.58
(1.54)
ꢀ111.7 1.54
(1.49)
6.99
6.26
6.27
6.47
5.92
20.07 195
15.73 145
15.77 131
256 390.3
220 381.9
312 364.8
215 387.0
170 232.6
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
17.16
14.08
88
90
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
10
11
15
16
17
19
20
ꢀ83.8 1.61
ꢀ111.7 1.53
ꢀ143.0 1.49
ꢀ143.0 1.48
ꢀ98.6 1.57
ꢀ99.5 1.57
ꢀ99.5 1.58
6.50
5.90
5.15
5.13
6.20
6.37
6.40
17.52
14.08
10.46 197
10.33 92
15.69 125
16.59
-
–
237 224.2
209 197.4
271 401.6
259 383.2
268 394.9
319 263.1
221 263.1
–
16.82 168
ACHTUNGTRENNUNG
21
6.41
6.34
4.42
5.75
16.89 200
230 253.5
152 253.5
228 682.8
142 585.7
ACHTUNGTRENNUNG
22
16.41
7.32
–
ACHTUNGTRENNUNG
25a
62
ACHTUNGTRENNUNG
25b
13.05 110
[a] Oxygen balance. [b] Calculated density; the experimental crystal den-
sity is shown in parentheses. [c] Velocity of detonation. [d] Detonation
pressure. [e] Melting point. [f] Decomposition temperature. [g] Heat of
formation.
and pyridine rings in its molecular structure. In general, pyr-
idine contributes 140.12 kJmolꢀ1 energy, whereas benzene
offers only 82.84 kJmolꢀ1; thus, the N-oxide-bearing pyri-
514
www.chemeurj.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 509 – 518

Thermally Stable Energetic 1,2,3-Triazole Derivatives
FULL PAPER
recorded at 400 MHz and 101 MHz, respectively, with the solvent reso-
nance as an internal standard (1H NMR: CDCl3 at d=7.26 ppm,
[D6]DMSO at d=2.50 and 3.50 ppm; 13C NMR: CDCl3 at d=77.0 ppm,
[D6]DMSO at d=44.0 ppm). IR spectra are reported in cmꢀ1. LCMS
spectra were obtained with an ionization voltage of 70ev; data are report-
ed in the form of m/z (intensity relative to base peak=100). Elemental
analysis was carried out on a FLASH EA 1112 analyzer. Melting points
and decomposition temperatures (DTA) were determined by using DSC–
TGA measurements. Single-crystal X-ray data were collected at 298 K on
SMART APEX CCD and Xcalibur Gemini Eos CCD single-crystal dif-
fractometers by using graphite-monochromated MoKa radiation
(0.71073 ꢁ).
pounds 7a and 19 showed good thermal stabilities
(>3008C). Compounds 10, 11, 19, and 22 decomposed with-
out melting. Owing to a large variation in their melting
(<928C) and decomposition temperatures (>1708C), com-
pounds 8a, 9, 16, and 25a could be useful as melt-cast explo-
sives.
Conclusion
X-ray crystallography: X-ray reflections for compounds 5a, 7a, 8a, and
20 were collected on a Bruker SMART APEX CCD diffractometer that
was equipped with a graphite monochromator and a Mo Ka fine-focus
sealed tube (l=0.71073 ꢁ). Data integration was done by using
SAINT.[20] The intensities of the absorption were corrected by using
SADABS.[21] Structure solution and refinement were carried out by using
Bruker SHELX-TL.[22] X-ray reflections for compounds 6a, 9, 21, 22, and
25a were collected on an Oxford Xcalibur Gemini Eos CCD diffractome-
ter by using Mo Ka radiation. Data reduction was performed by using
CrysAlisPro (version 1.171.33.55). The OLEX2–1.0[23] and SHELX-TL 97
programs were used to solve and refine the data. All non-hydrogen
In summary, a wide variety of new thermally stable nitro-
rich benzyl-/aryl- and pyridyl-tethered 1,2,3-triazole-based
energetic materials have been efficiently synthesized
through a cycloaddition reaction between their correspond-
ing readily available benzyl-/aryl- and pyridyl-tethered
azides and commercially available alkynes, followed by ni-
tration of the triazole derivatives; the molecules were thor-
oughly characterized by analytical and spectroscopic meth-
ods. The structures of most of these newly synthesized mole-
cules were determined by using X-ray diffraction analysis.
Most of the nitro derivatives of 1,2,3-triazoles decomposed
in the range 142–3198C; therefore, these molecules are con-
sidered to be thermally stable energetic materials. Most of
these compounds exhibited moderate detonation perform-
ance: Compound 5a (P=20.07 GPa, D=6.99 kmsꢀ1)
showed comparable detonation properties to TNT (P=
19.5 GPa, D=6.88 kmsꢀ1). Our predicted results revealed
that the synthesized compounds possessed high positive
HOFs; in particular, the pyridyl-tethered nitro derivative
showed a HOF of 682.8 kJmolꢀ1. Some of these molecules
might be useful as melt-cast explosives and energetic oxidiz-
ers, owing to their low melting points and high thermal sta-
bilities. Fabrication of complex structures with more triazole
moieties on pyridine templates is currently being pursued in
our laboratory.
ꢀ
atoms were refined anisotropically and the C H hydrogen atoms were
placed at fixed positions.
CCDC-895107 (5a), CCDC-895108 (6a), CCDC-895109 (7a), CCDC-
895110 (8a), CCDC-896656 (9), CCDC-895111 (20), CCDC-895112 (21),
CCDC-895113 (22), and CCDC-895114 (25a) contain the supplementary
crystallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Theoretical study: Density function theory (DFT) has been universally
applied to study energetic materials and has been shown to be reliable.
Electronic-structure calculations were performed with the Gaussian 09
suite.[24] The geometries of the molecules were calculated at the B3LYP
level in conjugation with the 6–311G** basis set.[25] The optimized ge
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
suite for density calculations by using the CVFF force field[26] The heats
of formation of the triazole derivatives were obtained by using semi-em-
pirical methods (Austin Model 1 (AM1), Parameterization Method 3
(PM3), and Parameterization Method 6 (PM6)).[27] The detonation prop-
erties (D and P) of the compounds were evaluated by using the Kamlet–
Jacobs equations,[28] based on their predicted densities and HOFs, accord-
ing to Equations (2) and (3), where D is detonation velocity (kmsꢀ1), P is
the detonation pressure (GPa), N is the number of moles of gaseous det-
onation products per gram of explosives, M is the average molecular
weight of the gaseous products, Q is the chemical energy of detonation
(calgꢀ1), which is defined as the difference between the HOFs of the
products and the reactants, and 1 is the density of the explosive (gcmꢀ3):
Experimental Section
Caution! Working with azides should always be done carefully. Organic
azides, in particular those of low molecular weight or with high nitrogen
content, are potentially explosive. Heat, light, and pressure can cause de-
composition of the azides. Any experiments in which azides are to be
heated in the presence of copper should involve the use of a blast shield.
All nitro derivatives of 1,2,3-triazoles are dangerous when heating at
high temperature. We prepared all of these compounds on the milligram
scale. None of the compounds described herein exploded or were deto-
nated during the course of this research; in any case, these materials
should be handled with care by using proper safety precautions. Safety
shields, safety glasses, face shields, leather gloves, and protective clothing,
such as leather suits and ear plugs, must be worn. Ignoring safety precau-
tions can lead to serious injury.
0:5
D ¼ 1:01ðNM0:5Q0:5
Þ ð1þ1:301oÞ
ð2Þ
ð3Þ
P ¼ 1:551o2NM0:5Q0:5
General procedure for the cycloaddition reaction: A mixture of the azide
(1.0 equiv), trimethylsilyl (TMS)-acetylene (1.5 equiv), potassium carbo-
nate (1.2 equiv), CuSO4 (0.2 equiv), and sodium ascorbate (0.4 equiv)
was dissolved in MeOH/water (1:1, 5 mL for 10 mmol) in a 20 mL vial.
The vial was sealed with a screw cap and the resulting mixture was stir-
red rapidly at RT for 24 h. Upon completion of the reaction, aqueous
ammonium hydroxide (5%) was added to the reaction mixture, the or-
ganic layer was separated, and the aqueous layer was extracted with
EtOAc (3 times). The combined extracts were washed with water (twice)
and brine and dried over Na2SO4. The solvent was filtered off and evapo-
rated under reduced pressure. The crude residue was purified by column
chromatography on silica gel.
General: Unless otherwise noted, all of the chemicals were purchased
from Sigma Aldrich Ltd. and used as received. All of the reactions were
performed in oven-dried round-bottomed flasks. Commercial-grade sol-
vents were distilled prior to use. Column chromatography was performed
on either 100–200 Mesh or 230–400 Mesh silica gel. Thin layer chroma-
tography (TLC) was performed on silica gel GF254 plates. Visualization
of the spots on the TLC plates was accomplished with UV light (254 nm)
and with staining in an I2 chamber. 1H NMR and 13C NMR spectra were
Chem. Eur. J. 2013, 19, 509 – 518
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
515

A. K. Sahoo et al.
According to this above-mentioned procedure, known triazole com-
pounds 3a–3g, 4a, and 13a–13g were prepared in good-to-excellent
yields.
[M+1]+, 202 (19), 192 (3), 172 (5), 159 (3); elemental analysis calcd (%)
for C9H7N5O4: C 43.38, H 2.83, N 28.11; found: C 43.45, H 2.81, N 28.05.
1-(4-Methoxy-3,5-dinitrobenzyl)-1H-1,2,3-triazole (9): 1.12 g, 71% Yield;
yellow solid; m.p. 908C; DTA=1708C (exotherm); Rf =0.51 (n-hexane/
EtOAc, 1:1) 1H NMR (400 MHZ, [D6]DMSO): d=7.98 (s, 2H), 7.79 (s,
1H), 7.72 (s, 1H), 5.69 (s, 2H), 3.98 ppm (s, 3H); 13C NMR (400 MHz,
[D6]DMSO): d=147.6, 145.3, 134.6, 131.9, 128.6, 124.4, 64.9, 51.7 ppm;
IR (KBr): n˜ =3113, 1537, 1348, 1269, 1082, 979, 717 cmꢀ1; MS (EI): m/z
(%): 280 (100) [M+1]+, 211 (45), 102 (28), 70 (26); elemental analysis
calcd (%) for C10H9N5O5: C 43.02, H 3.25, N 25.08; found: C 43.15,
H 3.31, N 25.19.
2,6-Bis((1H-1,2,3-triazol-1-yl)methyl)pyridine (24a): M.p. 65–688C; Rf =
0.57 (EtOAc); 1H NMR (400 MHz, CDCl3): d=7.65–7.54 (m, 5H), 7.02
(d, J=7.6 Hz, 2H), 5.57 ppm (s, 4H); 13C NMR (101 MHz, CDCl3): d=
154.6, 138.6, 134.1, 124.5, 121.7, 54.9 ppm; IR (KBr): n˜ =1591, 1454, 1217,
1087, 1028, 800, 765, 690 cmꢀ1; MS (EI): m/z (%): 242 (100) [M+1]+, 214
(19), 186 (14), 173 (8), 145 (16); elemental analysis calcd (%) for
C11H11N7: C 54.76, H 4.60, N 40.64; found: C 54.63, H 4.68, N 40.52.
Diethyl-2,2’-(1,1’-(pyridine-2,6-diylbis(methylene))bis(1H-1,2,3-triazole-
4,1-diyl)) diacetate (24b): Rf =0.56 (EtOAc); 1H NMR (400 MHz,
CDCl3): d=7.72 (s, 2H), 7.66 (t, J=8.0 Hz, 1H), 7.11 (d, J=7.6 Hz, 2H),
5.59 (s, 4H), 5.17 (s, 4H), 2.28 (q, J=7.6 Hz, 4H), 1.06 ppm (t, J=7.6 Hz,
6H); 13C NMR (101 MHz, CDCl3): d=173.7, 154.3, 142.7, 138.4, 124.7,
121.5, 57.1, 54.6, 26.9, 8.60 ppm; IR (neat): n˜ =2982, 1738, 1462, 1182,
1051, 781 cmꢀ1; MS (EI): m/z (%): 414 (45) [M+1]+, 436 (100) [M+Na]+;
elemental analysis calcd (%) for C19H23N7O4: C 55.20, H 5.61, N 23.72;
found: C 55.36, H 5.65, N 23.65.
1-(4-Methoxy-3,5-dinitrobenzyl)-4-nitro-1H-1,2,3-triazole (10): 1.02 g,
75% Yield; yellow solid; DTA=2378C (exotherm); Rf =0.71 (n-hexane/
EtOAc, 1:1); 1H NMR (400 MHz, [D6]DMSO): d=8.96 (s, 1H), 8.84 (s,
1H), 8.80 (s, 1H), 5.88 (s, 2H), 4.28 ppm (s, 3H); 13C NMR (101 MHz,
[D6]DMSO): d=160.2, 151.3, 138.5, 132.1, 131.8, 127.5, 124.9, 123.2, 50.7,
46.9 ppm; IR (KBr): n˜ =3111, 1610, 1591, 1531, 1352, 1074, 792, 688 cmꢀ1
;
MS (EI): m/z (%): 325 (100) [M+1]+, 116 (22), 102 (20), 84 (38), 70 (22);
elemental analysis calcd (%) for C10H8N6O7: C 37.05, H 2.49, N 25.92;
found: C 37.12, H 2.55, N 25.86.
General procedure for the synthesis of compounds 5a–11: A mixture of
98% sulfuric acid (15 mL) and 70% nitric acid (10 mL) was added to
compound 3 (12 mmol) at 08C and the reaction was carried out under
the respective conditions shown in the Table 2. Upon completion, the re-
action mixture was cooled by the addition of ice and neutralized with a
saturated aqueous solution of NaHCO3. The organic layer was separated
and the aqueous layer was extracted with the minimum amount of
EtOAc (3ꢂ20 mL). The combined extracts were washed with water (2ꢂ
20 mL) and brine (25 mL) and dried over Na2SO4. The solvent was fil-
tered off and evaporated under vacuum. The crude residue was purified
by column chromatography on silica gel to afford the desired nitration
products in good overall yields. A similar procedure was adopted for the
nitration reactions that were carried out with a mixture of 95% nitric
acid and 98% sulfuric acid.
1-(2-Methoxy-3,5-dinitrobenzyl)-1H-1,2,3-triazole (11): 0.21 g, 48%
Yield; yellow solid; DTA=2098C (exotherm); Rf =0.67 (n-hexane/
EtOAc, 3:7); 1H NMR (400 MHz, [D6]DMSO): d=8.78 (d, J=2.4 Hz,
1H), 8.36 (d, J=2.0 Hz, 1H), 8.26 (s, 1H), 7.79 (s, 1H), 5.85 (s, 2H),
3.88 ppm (s, 3H); 13C NMR(101 MHz, [D6]DMSO): d=156.2, 142.9,
142.6, 134.1, 134.0, 129.4, 126.2, 122.1, 63.7, 47.7 ppm; IR (neat): n˜ =1608,
1539, 1481,1346, 1265, 1091, 985 cmꢀ1; MS (EI): m/z (%): 281 (19)
[M+1]+, 280 (100) [M]+, 235 (7), 207 (8), 162 (5), 116 (9), 84 (16); ele-
mental analysis calcd (%) for C10H9N5O5: C 43.02, H 3.25, N 25.08;
found: C 43.11, H 3.19, N 25.15.
General procedure for the synthesis of compounds 15–22: A mixture of
98% sulfuric acid (15 mL) and 95% nitric acid (10 mL) was added to
compound 13 (12 mmol) at 08C and the reaction was carried out under
the respective conditions shown in the Table 4. Upon completion, the re-
action mixture was cooled by the addition of ice and neutralized with a
saturated aqueous solution of NaHCO3. The organic layer was separated
and the aqueous layer was extracted with the minimum amount of
EtOAc (3ꢂ20 mL). The combined extracts were washed with water (2ꢂ
20 mL) and brine (25 mL) and dried over Na2SO4. The solvent was fil-
tered off and evaporated under vacuum. The crude residue was purified
by column chromatography on silica gel to afford the desired nitration
products in good overall yields.
1-(2,4-Dinitrobenzyl)-4-nitro-1H-1,2,3-triazole (5a): 0.58 g, 15% Yield;
colorless solid; m.p. 1958C; DTA=2568C (exotherm); Rf =0.60 (n-
hexane/EtOAc, 1:1); 1H NMR (400 MHz, [D6]DMSO): d=9.38 (s, 1H),
8.84 (s, 1H), 8.52 (d, J=8.0 Hz, 1H), 7.50 (d, J=8.8 Hz, 1H), 6.22 ppm
(s, 2H); 13C NMR (101 MHz, [D6]DMSO): d=153.5, 143.2, 134.9, 130.9,
124.1, 57.6 ppm; IR (KBr): n˜ =3412, 3092, 1518, 1342, 1086, 1047, 829,
723 cmꢀ1; MS (EI): m/z (%): 295 (100) [M+1]+, 282 (6), 250 (60), 231
(14), 181 (4), 73 (48); elemental analysis calcd (%) for C9H6N6O6:
C 36.74, H 2.06, N 28.57; found: C 36.85, H 2.01, N 28.64.
1-(2,4-Dinitrobenzyl)-1H-1,2,3-triazole (6a): 1.23 g, 39% Yield; colorless
solid; m.p. 1528C; DTA=2208C (exotherm); Rf =0.28 (n-hexane/EtOAc,
1:1); 1H NMR (400 MHz, [D6]DMSO): d=8.82 (d, J=2.4 Hz, 1H), 8.52
(dd, J=2.4, 8.8 Hz, 1H), 8.23 (s, 1H), 7.85 (s, 1H), 7.11 (d, J=8.8 Hz,
1H), 6.14 ppm (s, 2H); 13C NMR (101 MHz, [D6]DMSO): d=147.8,
147.6, 138.4, 138.3, 134.3, 131.6, 131.5, 128.8, 126.6, 120.8, 50.0 ppm; IR
(KBr): n˜ =3132, 1608, 1535, 1346, 1221, 1070, 839, 729 cmꢀ1; MS (EI):
m/z (%): 250 (100) [M+1]+, 195 (3), 181 (3); elemental analysis calcd
(%) for C9H7N5O4: C 43.38, H 2.83, N 28.11; found: C 43.32, H 2.85,
N 28.26.
1-(3,4-Dinitrophenyl)-1H-1,2,3-triazole (17): 0.19 g, 18% Yield; brown
solid; m.p. 1258C; DTA=2688C (exotherm); Rf =0.48 (n-hexane/EtOAc,
2:1); 1H NMR (400 MHz, CDCl3): d=9.10 (br s, 1H), 9.03 (br d, J=
4.0 Hz, 2H), 8.31 (br s, 1H), 7.99 ppm (br s, 1H); 13C NMR (101 MHz,
CDCl3): d=149.3, 138.6, 135.8, 121.9, 120.1, 117.9 ppm; IR (KBr): n˜ =
3084, 2961, 1635, 1558, 1261, 1024, 798 cmꢀ1; MS (EI): m/z (%): 234 (38)
[Mꢀ1]+, 228 (31), 206 (100), 183 (16), 87 (7); elemental analysis calcd
(%) for C8H5N5O4: C 40.86, H 2.14, N 29.78; found: C 40.75, H 2.18,
N 29.71.
1-(4-Methoxy-3,5-dinitrophenyl)-1H-1,2,3-triazole (19): 1.10 g, 85%
Yield; yellow solid; DTA=3198C (exotherm); Rf =0.57 (n-hexane/
EtOAc, 1:1); 1H NMR (400 MHz, [D6]DMSO): d=9.03 (s, 1H), 8.91 (s,
2H), 8.06 (s, 1H), 4.00 ppm (s, 3H); 13C NMR (101 MHz, [D6]DMSO):
d=146.1, 145.4, 135.6, 132.2, 124.5, 121.3, 65.1 ppm; IR (KBr): n˜ =3157,
1541, 1346, 1271, 1053, 783 cmꢀ1; MS (EI): m/z (%): 266 (21) [M+1]+,
265 (100) [M], 250 (39), 236 (26), 221 (13), 205 (5); elemental analysis
calcd (%) for C9H7N5O5: C 40.76, H 2.66, N 26.41; found: C 40.82,
H 2.61, N 26.31.
1-(3,5-Dinitrobenzyl)-1H-1,2,3-triazole (7a): 0.62 g, 20% Yield; colorless
solid; m.p. 1318C; DTA=3128C (exotherm); Rf =0.20 (n-hexane/EtOAc,
1
1:1); H NMR (400 MHz, [D6]DMSO): d=8.78 (s, 1H), 8.59 (s, 2H), 8.33
(s, 1H), 7.81 (s, 1H), 5.95 ppm (s, 2H); 13C NMR (101 MHz,
[D6]DMSO): d=148.7, 140.6, 134.3, 129.1, 126.1, 118.8, 51.3 ppm; IR
(KBr): n˜ =3140, 3076, 1547, 1346, 1072, 929, 800, 729 cmꢀ1; MS (EI): m/z
(%): 250 (100) [M+1]+, 234 (5), 220 (3), 177 (5), 121 (3), 89 (9); elemen-
tal analysis calcd (%) for C9H7N5O4: C 43.38, H 2.83, N 28.11; found:
C 43.51, H 2.88, N 28.07.
1-(3-Methoxy-2,6-dinitrophenyl)-1H-1,2,3-triazole (20): 0.49 g, 33%
Yield; yellow solid; m.p. 1688C; DTA=2218C (exotherm); Rf =0.65 (n-
hexane/EtOAc, 4:6); 1H NMR (400 MHz, [D6]DMSO): d=8.68 (br s,
1H), 8.63 (d, J=9.6 Hz, 1H), 8.01 (s, 1H), 7.86 (d, J=9.6 Hz, 1H),
4.13 ppm (s, 3H); 13C NMR (101 MHz, [D6]DMSO): d=155.2, 137.7,
137.0, 134.6, 130.2, 128.9, 124.9, 116.7, 59.0 ppm; IR (KBr): n˜ =3124,
1614, 1342, 1078, 989, 794, 652 cmꢀ1; MS (EI): m/z (%): 266 (58) [M+1]+,
242 (26), 226 (83), 210 (100), 194 (91), 163 (72), 149 (85); elemental anal-
1-(3,4-Dinitrobenzyl)-1H-1,2,3-triazole (8a): 0.31 g, 9% Yield; yellow
semi-solid; m.p. 888C; DTA=2158C (exotherm); Rf =0.10 (n-hexane/
EtOAc, 1:1); 1H NMR (400 MHz, [D6]DMSO): d=8.30 (s, 1H), 8.23 (d,
J=8.4 Hz, 1H), 8.18 (s, 1H), 7.81 (s, 1H), 7.77 (d, J=8.4 Hz, 1H),
5.89 ppm (s, 2H); 13C NMR (101 MHz, [D6]DMSO): d=143.8, 142.5,
141.8, 134.3, 133.9, 126.7, 126.1, 125.3, 51.5 ppm; IR (KBr): n˜ =2928,
1541, 1369, 1219, 1026, 846, 804 cmꢀ1; MS (EI): m/z (%): 250 (100)
516
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Thermally Stable Energetic 1,2,3-Triazole Derivatives
FULL PAPER
ysis calcd (%) for C9H7N5O5: C 40.76, H 2.66, N 26.41; found: C 40.71,
H 2.59, N 26.35.
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1-(3-Methoxy-2,4-Dinitrophenyl)-1H-1,2,3-triazole (21): 0.69 g, 46%
Yield; yellow solid; m.p. 2008C; DTA=2308C (exotherm); Rf =0.40 (n-
hexane/EtOAc, 7:3); 1H NMR (400 MHz, CDCl3): d=8.88 (s, 1H), 8.77
(br s, 1H), 8.05 (br s, 1H), 7.87 (s, 1H), 4.11 ppm (s, 3H); 13C NMR
(101 MHz, CDCl3): d=155.9, 138.3, 136.0, 134.7, 134.3, 127.3, 124.1,
114.4, 59.1 ppm; IR (KBr): n˜ =3097, 1620, 1531, 1350, 1232, 1072,
806 cmꢀ1; MS (EI): m/z (%): 266 (68) [M+1]+, 242 (45), 226 (57), 210
(72), 194 (92), 164 (100), 149 (72); elemental analysis calcd (%) for
C9H7N5O5: C 40.76, H 2.66, N 26.41; found: C 40.85, H 2.63, N 26.35.
1-(2-Methoxy-3,5-dinitrophenyl)-1H-1,2,3-triazole (22): 1.24 g, 82%
Yield; yellow solid; DTA=1528C (exotherm); Rf =0.57 (n-hexane/
EtOAc, 1:1); 1H NMR (400 MHz, CDCl3): d=8.98–8.95 (m, 1H), 8.80
(br s, 1H), 8.69 (s, 1H), 8.07 (s, 1H), 3.63 ppm (s, 3H); 13C NMR
(101 MHz, CDCl3): d=151.5, 144.0, 142.4, 134.8, 132.1, 127.8, 126.1,
125.7, 121.9, 63.4 ppm; IR (KBr): n˜ =3155, 1547, 1350, 1261, 1049, 978,
733 cmꢀ1; MS (EI): m/z (%): 266 (58) [M+1]+, 223 (23), 129 (56), 116
(12), 97 (100), 74 (6); elemental analysis calcd (%) for C9H7N5O5:
C 40.76, H 2.66, N 26.41; found: C 40.65, H 2.69, N 26.52.
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General procedure for the formation of the N-oxides: A solution of the
bistriazole-containing pyridine (24) (1.0 equiv) and m-chloroperbenzoic
acid (mCPBA, 1.5 equiv) in CHCl3 (2 mL for 1 mmol) was placed in a
10 mL screw-capped vial. The vial was sealed and the mixture was stirred
at 708C for 48 h. Upon completion of the reaction, the mixture was
cooled and dissolved in water. The organic layer was separated and the
aqueous layer was extracted with Et2O (twice). The combined extracts
were washed with water and brine and dried over Na2SO4. The solvent
was filtered off and evaporated under reduced pressure. The crude resi-
due was purified by column chromatography on silica gel. The desired N-
oxide products were obtained in good yields.
2,6-Bis((1H-1,2,3-triazol-1-yl)methyl)pyridine 1-oxide (25a): 0.08 g, 35%
Yield; colorless solid; m.p. 628C; DTA=2288C (exotherm); Rf =0.68
(CHCl3/MeOH, 9:1); 1H NMR (400 MHz, CDCl3): d=7.94 (s, 2H), 7.78
(s, 2H), 7.27 (br s, 1H), 7.12 (d, J=8.0 Hz, 2H), 5.87 ppm (s, 4H);
13C NMR (101 MHz, CDCl3): d=145.8, 134.2, 125.9, 125.6, 125.4,
48.4 ppm; IR (KBr): n˜ =2852, 1693, 1417, 1350, 1217, 1028, 808 cmꢀ1; MS
(EI): m/z (%): 258 (100) [M+1]+, 242 (16), 230 (14), 174 (11), 145 (8); el-
emental analysis calcd (%) for C11H11N7O5: C 51.36, H 4.31, N 38.11;
found: C 51.28, H 4.26, N 38.29.
2,6-Bis((4-(nitromethyl)-1H-1,2,3-triazol-1-yl)methyl)pyridine
1-oxide
(25b): 0.04 g, 41% Yield; pale-yellow solid; m.p. 1108C; DTA=1428C
(exotherm); Rf =0.72 (CHCl3/MeOH, 9:1); 1H NMR (400 MHz,
[D6]DMSO): d=8.14 (s, 2H), 7.38–7.27 (m, 3H), 5.79 (s, 4H), 5.58 ppm
(s, 4H); 13C NMR (101 MHz, [D6]DMSO): d=145.0, 139.6, 126.8, 126.7,
126.0, 65.6, 48.8 ppm; IR (KBr): n˜ =2924, 1724, 1641, 1385, 1261, 1111,
1022, 850, 796 cmꢀ1; MS (EI): m/z (%): 375 (100) [M]+, 374 (100)
[Mꢀ1]+, 356 (13), 343 (5), 327 (24); elemental analysis calcd (%) for
C13H13N9O5: C 41.60, H 3.49, N 33.59; found: C 41.75, H 3.56, N 33.41.
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A.S.K., V.D.G., and S.S. thank ACRHEM, the University of Hyderabad,
for financial support. The authors thank Prof. S. P. Tewari, Director,
ACRHEM for his encouragement. Prof. M. Durga Prasad and Prof. S.
Mahapatra are thanked for their support and valuable suggestions. We
also thank the CMSD and the School of Chemistry, the University of Hy-
derabad, for providing computational and experimental facilities. We ap-
preciate the support of Dr. Raghaviah, Dr. Naba K. Nath, Mr. S. Sudalai
Kumar, Mr. D. Maddileti, and Mr. P. Krishna Chary (School of Chemis-
try, the University of Hyderabad) for performing the X-ray crystallogra-
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Received: September 7, 2012
Published online: November 26, 2012
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Chem. Eur. J. 2013, 19, 509 – 518