Synthesis, single crystal structure and performance of N-substituted derivatives of dinitroimidazole

Article abstract of DOI:10.1039/c3nj00521f

The N-substituted derivatives of dinitroimidazoles have been synthesized for application as energetic materials. The synthesized compounds were fully characterized by ¹H ¹³C NMR spectroscopy and elemental analysis. Most of them were determined by single crystal X-ray diffraction. The calculated densities of the compounds range between 1.89 and 1.91 g cm ^-3 and the experimental densities between 1.75 and 1.84 g cm ^-3, as obtained by X-ray crystallographic analysis. Notably, densities of the N-substituted derivatives of dinitroimidazoles are increased when two amino groups are introduced but decreased when one amino group is introduced.

Full text of DOI:10.1039/c3nj00521f

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Synthesis, single crystal structure and performance of
N-substituted derivatives of dinitroimidazole†
Cite this: NewJ.Chem., 2013,
37, 2837
Kehui Hou,z Congming Maz and Zuliang Liu*
The N-substituted derivatives of dinitroimidazoles have been synthesized for application as energetic
materials. The synthesized compounds were fully characterized by 1H 13C NMR spectroscopy and
elemental analysis. Most of them were determined by single crystal X-ray diffraction. The calculated
densities of the compounds range between 1.89 and 1.91 g cmꢀ3 and the experimental densities
between 1.75 and 1.84 g cmꢀ3, as obtained by X-ray crystallographic analysis. Notably, densities of the
N-substituted derivatives of dinitroimidazoles are increased when two amino groups are introduced but
decreased when one amino group is introduced.
Received (in Victoria, Australia)
15th May 2013,
Accepted 20th June 2013
DOI: 10.1039/c3nj00521f
www.rsc.org/njc
using triiodoimidazole as substrate. R. Duddu and co-workers6
developed a new, molten-state nitration method for the synthesis
Introduction
The synthesis and development of new, insensitive energetic
materials that contain aromatic nitrogen-containing hetero-
cyclic core units have attracted attention due to their more
favorable elemental composition with relatively higher energetic
performance with regard to oxygen balance, density, and other
thermodynamic properties when compared to their carbon-only
analogous aromatic compounds.1–4
of 1-methyl-2,4,5-trinitroimidazole. 1-(2,4,6-Tri-nitrophenyl)-2,4-
dinitroimidazole was obtained by the reaction of picryl fluoride
with 2,4-dinitroimidazole in the literature, the same as for
1-(2,4,6-trinitrophenyl)-4,5-dinitroimidazole.12
The substituted combination of amino and nitro groups
provides the inter and intra molecular hydrogen bonding that
stabilizes the molecule and increases the crystal density. It is
with this background and in continuation of our effort aimed at
synthesis of new dinitroimidazole-based energetic materials
that we have focused on the 2,4- and 4,5-dinitroimidazoles
with one 2,4,5-trinitrophenyl substituent including either 0,
1 or 2 amino groups inside, evaluated their performance by
using DFT and the nitrogen equivalent equation, analyzed the
single crystal structure and laid special stress on studying the
effect of substituent groups on the spatial arrangement.
It has been reported in the literature that imidazole deriva-
tives with two or more than two nitro groups have been
predicted to be highly powerful, but insensitive explosives.5–9
4,5-Dinitroimidazole crystallizes with two crystallographically
unique molecules in the monoclinic space group P21/n
with unit cell parameters a = 11.5360(8) Å, b = 9.071(1) Å,
c = 11.822(1) Å, Z = 8, and has a density of 1.781 g cmꢀ3 10
.
2,4-Dinitroimidazole crystallizes in the orthorhombic space
group Pbca with unit cell parameters a = 110.127(2) Å, b =
18.497(2) Å, c = 6.333(2) Å, Z = 8, and has a density of 1.770 g cmꢀ3 11
.
Results and discussion
Theoretical study
Cho et al.’s study5 showed that 1-methyl-2,4,5-trinitroimidazole is a
promising candidate as a highly insensitive explosive, with explosive
performance comparable to that of Hexogen (RDX). H. S. Jadhav
and co-workers2 reported the synthesis and characterization of
N-methyl, N-ester and N-picryl derivatives of 2,4,5-trinitroimidazole
The heat of formation (HOF) and density are important para-
meters in evaluating the performance of energetic materials.
We have calculated energetic properties of the compounds 1–6
by using DFT. The gas-phase HOF values (DHof gas) have been
predicted by designing appropriate isodesmic reactions.13,14
Calculations were carried out using the Gaussian 09 program
suite.15 The geometry optimization of the structures and fre-
quency analyses were carried out using the B3LYP functional
with the 6-31G* basis set.16 All of the optimized structures were
characterized by true local energy minima on the potential-
energy surface without imaginary frequencies. The designed
School of Chemical Engineering, Nanjing University of Science and Technology,
Nanjing 210094, PR China. E-mail: liuzl@mail.njust.edu.cn;
Fax: +86-25-8431-5030; Tel: +86-25-8431-8865
† Electronic supplementary information (ESI) available. CCDC 884546–884549
and 888387. For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/c3nj00521f
‡ These authors contributed equally to this work and should be considered
co-first authors.
c
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isodesmic reactions for the prediction of (DHof gas) are dis- number of moles of oxygen required by a compound in excess
cussed in the ESI.† to the oxygen chemically bound within the molecule for
Detonation velocity (D) and detonation pressure (P) are the complete combustion (negative OB) or excess number of moles
most important targets for scaling the detonation characteristics of oxygen chemically bound within a molecule more than
of energetic materials. For the explosives with CHNO elements, required for its complete combustion (positive OB). The sensi-
the Kamlet–Jacobs empirical equations17 and the nitrogen tivity, strength, and stability of an explosive are all to some
equivalent equation (NE equation)18 were used to determine extent dependent upon the oxygen balance. Although all of the
these parameters.
described compounds in this study have negative OB values,
most of them have a better oxygen balance than TNT (ꢀ74%).
The enthalpy of formation is one of the most important
parameters to be considered in the design of energetic materials.
Compounds 1 to 6 have positive heats of formation. The
calculated densities of the other compounds range between
Kamlet–Jacobs empirical equations:
D = 1.01 (NM0.5 0.5 0.5(1 + 1.30ro)
Q )
2
P = 1.55ro NM0.5Q0.5
where D is the detonation velocity in km sꢀ1, P is the detonation 1.89 and 1.91 g cmꢀ3 and the experimental densities between
pressure in GPa, N is moles of gaseous detonation products per 1.75 and 1.84 g cmꢀ3, as obtained by X-ray crystallographic
gram of explosives, M is the average molecular weight of analysis. The calculated detonation pressures (P) for the
gaseous products, Q is the energy of explosion in J gꢀ1 of the dinitroimidazole derivatives fall in the range of 31.36 to 32.82 GPa
explosive and ro is the crystal density in g cmꢀ3. N, M and Q are and the detonation velocities (D) are distributed from 8.28 to
determined according to the largest exothermic principle, i.e., 8.48 km sꢀ1. All of those are close to the empirical calculation,
for the explosives with CHNO elements, all the N atom converts 29.12 to 32.49 GPa and 8.11 to 8.44 km sꢀ1, respectively,
into N2, the O atom forms H2O with the H atom first and the predicted with the nitrogen equivalent equation.
remainder forms CO2 with the C atom. The remainder of the
X-ray crystallography
C atom will exist in solid state if the O atom does not satisfy full
oxidation of the C atom. The remainder of the O atom will exist The colorless single crystals of title compounds were selected
as O2 if the O atom is superfluous.
for X-ray diffraction analysis. The data were collected using a
Nonius cad4 detector equipped with a graphite-monochromatic
MoKa radiation (l = 0.71073 Å) using a o/2y scan mode at
293(2) K. The structure was solved by direct methods and
expanded by difference Fourier techniques with SHELXL-97
program. The non-hydrogen atoms were refined anisotropically,
and the hydrogen atoms were added according to the theoretical
models. The structure was refined by full-matrix least-squares
Nitrogen equivalent equation (NE equation):
P
D = (690 + 1160r0)
N
P
P = 1.092(r0 N)2 ꢀ 0.574
P
P
N = (100 xiNi)/M
in which D represents the detonation velocity of an explosive techniques on F2 with SHELXL-97. Crystallographic data for
in m sꢀ1, r0 represents the density of an explosive in g cmꢀ3
,
compounds 1, 3, 4, 5 and 6 are summarized in Table 2. Selected
P
N represents the nitrogen equivalent of the detonation bond lengths and angles for compounds are listed in the ESI.†
products, Ni is the nitrogen equivalent index of a certain Further information concerning the crystal-structure determina-
detonation product, xi is the mole number of a certain detona- tions in CIF format is available from the Cambridge Crystallo-
tion product produced by one mole of the explosive.
graphic Data Centre.19 Compounds 1, 3, 4, 5 and 6 are also
characterized by a three-dimensional network.
Energetic properties
The bonds of C(1)–N(3), C(3)–N(4) of the nitro groups in 1 are
The energetic properties data of the compounds are listed in not coplanar with the imidazole ring and displaced by 0.019 Å
Table 1. When compared with compound 4, it appears that and 0.027 Å from the imidazole ring, respectively. The 2- and
introduction of an additional amino group in 5 and 6 increases 4-nitro groups are also twisted out of the imidazole plane by
the density but decreases the performance. A similar trend is 6.201 and 12.351, respectively. The bonds of C(5)–N(5), C(7)–N(6)
observed for compounds 1, 2, and 3. Oxygen balance (OB) is the and C(9)–N(7) of the nitro groups are not coplanar with the
Table 1 Calculated energetic properties of dinitroimidazole derivatives
Compound
OBa [%]
HOFb [kJ molꢀ1
]
V [cm3 molꢀ1
]
Density [g cmꢀ3
]
Dc [km sꢀ1
]
Pd [GPa]
Qe [J gꢀ1
]
1
2
3
4
5
6
ꢀ41.19
ꢀ41.67
ꢀ42.11
ꢀ41.19
ꢀ41.67
ꢀ42.11
251.9016
213.3052
180.4869
277.1873
236.0061
205.3951
194.9999
200.6145
209.3913
194.577
202.3449
209.7513
1.892
1.914
1.906
1.896
1.898
1.902
8.27/8.11
8.32/—
8.27/8.44
8.31/8.30
8.29/8.16
8.28/8.40
31.26/29.12
31.81/—
31.36/32.49
31.57/30.99
31.43/29.57
31.42/31.99
1632.416
1413.471
1354.141
1497.748
1427.600
1369.06
a
b
c
Oxygen balance. Gas-phase HOF. Detonation velocity: the left value is calculated by DFT, the right value is calculated by the NE equation.
Detonation pressure: the left value is calculated by DFT, the right value is calculated by the NE equation. Chemical energy of detonation.
d
e
c
2838 New J. Chem., 2013, 37, 2837--2844
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Table 2 Crystallographic and refinement data for some compounds
1
3
4
5
6
CCDC
884547
C9H3N7O10
369.18
888387
C9H5N9O10
399.22
884548
C9H3N7O10
369.18
884549
C9H4N8O10
384.20
884546
C9H5N9O10
399.22
Formula
Mr [g molꢀ1
]
Temperature
Crystal system
Space group
293
Monoclinic
P21/N
293
Monoclinic
P21/N
293
293
293
Orthorhombic
P212121
Orthorhombic
P212121
Orthorhombic
P212121
a (Å)
b (Å)
8.7000(17)
11.397(2)
14.164(3)
1403.1(5)
4
9.0830(18)
11.395(2)
14.089(3)
1439.3(5)
4
8.2370(16)
12.791(3)
12.916(3)
1360.8(5)
4
8.4941(7)
12.7651(10)
13.3699(12)
1449.7(2)
4
9.1580(18)
12.318(3)
12.862(3)
1450.9(5)
4
c (Å)
V (Å3)
Z
Dc
1.748
0.0508, 0.1398
1.842
0.0505, 0.1081
1.802
0.0608, 0.1465
1.760
0.0780, 0.1453
1.828
0.0535, 0.1381
R1, wR2 (observed reflections)
Fig. 2 (a) Hydrogen-bonding scheme in the crystal structure of compound 1.
Thermal ellipsoids are set to 50% probability. Symmetry operators: (a) ꢀ1/2 ꢀ x,
1/2 + y, 1/2 ꢀ z (b) ꢀ1/2 + x, 1/2 ꢀ y, ꢀ1/2 + z; (b) the spatial arrangement of
four molecules in the unit cell of 1 viewed along the a axis.
Fig. 1 Molecular structure of 1-(2,4,6-trinitrophenyl)-2,4-dinitroimidazole (1).
Thermal ellipsoids are set to 50% probability.
Table 3 Hydrogen bonds present in compound 1
D–Hꢁ ꢁ ꢁA
d(D–H) [Å] d(Hꢁ ꢁ ꢁA) [Å] d(D–Hꢁ ꢁ ꢁA) [Å] +(D–Hꢁ ꢁ ꢁA) [1]
benzene ring and displaced by 0.013 Å, 0.017 Å and 0.028 Å
from the benzene ring, respectively. And the corresponding
nitro groups are also twisted out of the benzene plane by 28.221,
6.401 and 29.251, respectively. Furthermore, the angle of the
imidazole plane and the benzene plane is 86.321 (Fig. 1).
Further investigation on hydrogen bonds within the crystal
C2–H2Aꢁ ꢁ ꢁO8a 0.93
2.53
2.40
3.354(4)
3.324(4)
147
173
C8–H8Aꢁ ꢁ ꢁO6b 0.93
a
b
Symmetry operators: ꢀ1/2 ꢀ x, 1/2 + y, 1/2 ꢀ z. Symmetry operators:
ꢀ1/2 + x, 1/2 ꢀ y, ꢀ1/2 + z.
structure of compound 1 shows that three intermolecular benzene plane by 25.711, 7.601 and 33.721, respectively.
interactions including the formation of two intermolecular The bonds of C(2)–N(2) and C(4)–N(4) of the amino groups
hydrogen bonds, that is C8–H8Aꢁ ꢁ ꢁO6 and C2–H2Aꢁ ꢁ ꢁO8, could are also displaced by 0.039 and 0.153 Å from the benzene ring,
be observed (Fig. 2a and Table 3). Considering the withdrawing and the corresponding amino groups are twisted out of the
effect of two nitro groups on both sides of C(8E)–H, this benzene plane by 3.05 and 4.951, respectively. Furthermore,
hydrogen atom behaves as an approximately naked proton, the angle of the imidazole plane and the benzene plane is
and can easily form a hydrogen bond with the nitro group of 86.391 (Fig. 3).
another molecule, so is C(2E)–H. The spatial arrangement of
four molecules in the unit cell is presented in Fig. 2(b), as structure of compound 3 shows that four intermolecular inter-
viewed along the a axis. actions including the formation of four intermolecular hydrogen
Further investigation on hydrogen bonds within the crystal
The bonds of C(9)–N(8), C(8)–N(9) of the nitro groups in 3 bonds, that is N2–H2Bꢁ ꢁ ꢁO2, N4–H4Aꢁ ꢁ ꢁO1, N2–H2Aꢁ ꢁ ꢁO2 and
are displaced by 0.042 Å and 0.068 Å from the imidazole ring N4–H4Bꢁ ꢁ ꢁO5, could be observed (Fig. 4a). And intramolecular
and the 2- and 4-nitro groups are twisted out of the imidazole hydrogen bonds formed between NH2 and 40-NO2 are stronger
plane by 2.591 and 8.841, respectively. The bonds of C(1)–N(1), than 20(60)-NO2 (Table 4) because NH2 and 40-NO2 groups
C(3)–N(3) and C(5)–N(5) of the nitro groups are displaced are nearly coplanar with the benzene plane compared with
by 0.068 Å, 0.126 Å and 0.157 Å from the benzene ring 20(60)-NO2. The spatial arrangement of four molecules in the
and the corresponding nitro groups are twisted out of the unit cell viewed along the a axis is presented in Fig. 4(b).
c
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Fig. 5 Molecular structure of 1-(2,4,6-trinitrophenyl)-4,5-dinitroimidazole (4).
Thermal ellipsoids are set to 50% probability.
Fig. 3 Molecular structure of 1-(3,5-diamino-2,4,6-trinitrophenyl)-2,4-dinitro-
imidazole (3). Thermal ellipsoids are set to 50% probability.
Fig. 6 (a) Hydrogen-bonding scheme in the crystal structure of compound 4.
Thermal ellipsoids are set to 50% probability. Symmetry operators: (a) 2 ꢀ x,
1/2 + y, 3/2 ꢀ z; (b) ꢀ1 + x, y, z; (b) the spatial arrangement of four molecules in
the unit cell of 4 viewed along the a axis.
Fig. 4 (a) Hydrogen-bonding scheme in the crystal structure of compound 3.
Thermal ellipsoids are set to 50% probability. Symmetry operators: (a) ꢀx, 1 ꢀ y,
1 ꢀ z; (b) ꢀ1/2 + x, 1/2 ꢀ y, 1/2 ꢀ z; (c) ꢀx, ꢀy, 2 ꢀ z; (b) the spatial arrangement
of four molecules in the unit cell of 3 viewed along the a axis.
Further investigation on hydrogen bonds within the crystal
structure of compound 4 shows that three intermolecular inter-
actions including the formation of two intermolecular hydrogen
bonds, that is C6–H6Aꢁ ꢁꢁO2 and C8–H8Aꢁ ꢁ ꢁO6, could be observed
(Fig. 6a and Table 5). The spatial arrangement of four molecules
in the unit cell viewed along the a axis (Fig. 6b) is different from
1 because 4-NO2 of imidazole formed a hydrogen bond not 2-H
of it. The bigger angle of 20-NO2 with the benzene plane (61.951)
may be another reason.
The bonds of C(2)–N(3), C(3)–N(4) of the nitro groups in 5
are displaced by 0.043 Å and 0.107 Å from the imidazole ring
and the 4- and 5-nitro groups are twisted out of the imidazole
plane by 1.931 and 35.491, respectively. The bonds of C(5)–N(5),
C(7)–N(6) and C(9)–N(8) of the nitro groups are displaced by 0.004,
0.025 and 0.015 Å from the benzene ring and the corresponding
Table 4 Hydrogen bonds present in compound 3
D–Hꢁ ꢁ ꢁA
d(D–H) [Å] d(Hꢁ ꢁ ꢁA) [Å] d(D–Hꢁ ꢁ ꢁA) [Å] +(D–Hꢁ ꢁ ꢁA) [1]
N2–H2Aꢁ ꢁ ꢁO3 0.86
N2–H2Bꢁ ꢁ ꢁO2 0.86
N2–H2Bꢁ ꢁ ꢁO2a 0.86
N4–H4Aꢁ ꢁ ꢁO4 0.86
N4–H4Aꢁ ꢁ ꢁO1b 0.86
N4–H4Bꢁ ꢁ ꢁO5 0.86
N4–H4Bꢁ ꢁ ꢁO5c 0.86
1.89
1.98
2.54
1.91
2.20
1.97
2.59
2.531(4)
2.610(4)
3.326(3)
2.534(3)
2.828(3)
2.619(4)
3.354(3)
130
129
152
128
130
131
149
a
b
Symmetry operators: ꢀx, 1 ꢀ y, 1 ꢀ z. Symmetry operators: ꢀ1/2 + x,
c
1/2 ꢀ y, 1/2 ꢀ z. Symmetry operators: ꢀx, ꢀy, 2 ꢀ z.
The bonds of C(2)–N(3), C(3)–N(4) of the nitro groups in 4
are displaced by 0.119 Å and 0.037 Å from the imidazole ring
and the 4- and 5-nitro groups are also twisted out of the
imidazole plane by 12.431 and 35.111, respectively. The bonds
of C(5)–N(5), C(7)–N(6) and C(9)–N(7) of the nitro groups are
displaced by 0.001 Å, 0.074 Å and 0.093 Å from the benzene ring and
the corresponding nitro groups are twisted out of the benzene plane
by 61.951, 2.071 and 7.431, respectively. Furthermore, the angle of
the imidazole plane and the benzene plane is 77.511 (Fig. 5).
Table 5 Hydrogen bonds present in compound 4
D–Hꢁ ꢁ ꢁA
d(D–H) [Å] d(Hꢁ ꢁ ꢁA) [Å] d(D–Hꢁ ꢁ ꢁA) [Å] +(D–Hꢁ ꢁ ꢁA) [1]
C6–H6Aꢁ ꢁ ꢁO2a 0.93
2.45
2.45
3.348(8)
3.373(7)
162
169
C8–H8Aꢁ ꢁ ꢁO6b 0.93
a
b
Symmetry operators: 2 ꢀ x, 1/2 + y, 3/2 ꢀ z. Symmetry operators:
ꢀ1 + x, y, z.
c
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Fig. 7 Molecular structure of 1-(3-amino-2,4,6-trinitrophenyl)-4,5-dinitroimid-
azole (5). Thermal ellipsoids are set to 50% probability.
nitro groups are also twisted out of the benzene plane by 6.181,
3.731 and 89.121, respectively. The bonds of C(8)–N(7) of the amino
group is also displaced by 0.038 Å from the benzene ring, and
twisted out of the benzene plane by 1.851. Furthermore, the angle
of the imidazole plane and the benzene plane is 80.791 (Fig. 7).
Further investigation on hydrogen bonds within the crystal
structure of compound 5 shows that three intermolecular inter-
actions including the formation of two weak intermolecular
hydrogen bonds, that is N7–H7Bꢁ ꢁ ꢁN2, could be observed
(Fig. 8a and Table 6). And in this case, we find that it is the
3-N of imidazole owing lone pair electrons that formed an
intramolecular hydrogen bond with NH2 of another molecule,
and the spatial arrangement of four molecules in the unit cell
(Fig. 8b) is looser than in compound 4 due to the nearly vertical
angle of 20-NO2 on the NH2 side with the benzene plane (89.121)
which does not form a hydrogen bond with NH2.
Fig. 9 Molecular structure of 1-(3,5-diamino-2,4,6-trinitrophenyl)-4,5-dinitro-
imidazole (6). Thermal ellipsoids are set to 50% probability.
The bonds of C(2)–N(3), C(3)–N(4) of the nitro groups in 6
are displaced by 0.016 Å and 0.014 Å from the imidazole ring and
the 4- and 5-nitro groups are also twisted out of the imidazole
plane by 0.691 and 33.51, respectively. The bonds of C(5)–N(5),
C(7)–N(7) and C(9)–N(9) of the nitro groups are displaced by
0.079 Å, 0.088 Å and 0.009 Å from the benzene ring and the
corresponding nitro groups are also twisted out of the benzene
plane by 14.831, 12.421, and 73.341, respectively. The bonds of
C(6)–N(6) and C(8)–N(8) of the amino groups are also displaced
by 0.117 and 0.048 Å from the benzene ring, and twisted out of
the benzene plane by 3.85 and 1.931, respectively. Furthermore,
the angle of the imidazole plane and the benzene plane is
77.191 (Fig. 9).
Further investigation on hydrogen bonds within the crystal
structure of compound 6 shows that four intermolecular inter-
actions including the formation of three intermolecular hydrogen
bonds, that is N6–H6Bꢁꢁ ꢁO9, N8–H8Aꢁ ꢁꢁO4 and N8–H8Bꢁ ꢁ ꢁN1,
could be observed (Fig. 10a and Table 7). The spatial arrangement
of four molecules in the unit cell (Fig. 10b) is the same as in 4 but
more compact than in 4 due to the intermolecular and intra-
molecular hydrogen bonds formed between NH2 and NO2. And it
is looser than in 3 due to the approximate vertical angle of 20-NO2
Fig. 8 (a) Hydrogen-bonding scheme in the crystal structure of compound 5.
Thermal ellipsoids are set to 50% probability. Symmetry operators: (a) 1/2 ꢀ x,
ꢀy, ꢀ1/2 + z; (b) the spatial arrangement of four molecules in the unit cell of 5
viewed along the a axis.
Table 6 Hydrogen bonds present in compound 5
D–Hꢁ ꢁ ꢁA
d(D–H) [Å] d(Hꢁ ꢁ ꢁA) [Å] d(D–Hꢁ ꢁ ꢁA) [Å] +(D–Hꢁ ꢁ ꢁA) [1]
Fig. 10 (a) Hydrogen-bonding scheme in the crystal structure of compound 6.
Thermal ellipsoids are set to 50% probability. Symmetry operators: (a) 1 + x, y, z;
(b) 1/2 ꢀ x, 1 ꢀ y, 1/2 + z; (c) ꢀx, 1/2 + y, 3/2 ꢀ z; (b) the spatial arrangement of
four molecules in the unit cell of 6 viewed along the a axis.
N7–H7Aꢁ ꢁ ꢁO8 0.86
2.04
2.30
2.639(11)
3.097(11)
126
153
N7–H7Bꢁ ꢁ ꢁN2a 0.86
a
Symmetry operators: 1/2 ꢀ x, ꢀy, ꢀ1/2 + z.
c
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Table 7 Hydrogen bonds present in compound 6
D–Hꢁ ꢁ ꢁA
d(D–H) [Å] d(Hꢁ ꢁ ꢁA) [Å] d(D–Hꢁ ꢁ ꢁA) [Å] +(D–Hꢁ ꢁ ꢁA) [1]
N6–H6Aꢁ ꢁ ꢁO7 0.86
N6–H6Bꢁ ꢁ ꢁO6 0.86
N6–H6Bꢁ ꢁ ꢁO9a 0.86
N8–H8Aꢁ ꢁ ꢁO8 0.86
N8–H8Aꢁ ꢁ ꢁO4b 0.86
N8–H8Bꢁ ꢁ ꢁO9 0.86
N8–H8Bꢁ ꢁ ꢁN1c 0.86
1.89
1.96
2.45
1.93
2.46
2.51
2.35
2.551(8)
2.580(8)
2.911(7)
2.540(8)
3.145(7)
3.015(8)
3.146(7)
132
128
114
127
137
118
154
a
b
Symmetry operators: 1 + x, y, z. Symmetry operators: 1/2 ꢀ x, 1 ꢀ y,
c
1/2 + z. Symmetry operators: ꢀx, 1/2 + y, 3/2 ꢀ z.
Fig. 11 DSC thermograms of compounds 1–3 (2,4-DNI derivatives, heating
rate: 10 1C minꢀ1).
with the benzene plane (73.341) which does not form a hydrogen
bond with adjacent NH2 but can form an intermolecular hydrogen
bond with NH2 of another molecule, making it different from 5.
Forming intermolecular hydrogen bonds in different ways
leads to different spatial arrangements of four molecules in the
unit cell. For compound 1, hydrogen atoms of imidazole and
benzene form intermolecular hydrogen bonds with –NO2 on the
benzene ring of another molecule. For 3, NH2 on the benzene
ring only forms intermolecular hydrogen bonds with –NO2 on
the benzene ring of another molecule. For 4, 4-NO2 of imidazole
formed hydrogen bonds with H on the benzene ring of another
molecule. For 5, NH2 only formed intermolecular hydrogen
bonds with N owing lone pair electrons on the imidazole ring
of another molecule. For 6, an amino group formed inter-
molecular hydrogen bonds both with 3-N owing lone pair
electrons on the imidazole ring of another molecule and
5-NO2 on the imidazole ring of the third molecule, and the
20-NO2 which has an approximately vertical angle with the
benzene plane forms intermolecular hydrogen bonds with
NH2 of the fourth molecule.
The results showed that when –NH2 groups are introduced
into the benzene ring, the spatial arrangement of four mole-
cules in the unit cell has changed. It also indicates that the
densities are increased when two amino groups are introduced
(Table 2, compounds 1 and 3, 4 and 6), due to the formation
of intermolecular and intramolecular hydrogen bonds, but
decreased when one amino group is introduced (Table 2, com-
pounds 4 and 5), due to the nearly vertical angle of NO2 on the
NH2 side with the benzene plane which does not form hydrogen
bonds with NH2.
Fig. 12 DSC thermograms of compounds 4–6 (4,5-DNI derivatives, heating
rate: 10 1C minꢀ1).
Conclusion
In summary, we have synthesized a number of dinitroimidazole
derivatives using simple, scalable methods without the need
for complicated purification procedures. Single-crystal X-ray
measurements were accomplished for compounds 1, 3, 4, 5
and 6 and deliver insights into their structural characteristics.
All of these derivatives have a relatively high decomposition
temperature (250 to 350 1C), and their thermal stability
decreased as the number of amino groups increased.
Experimental section
Caution
The titled compounds are energetic materials and tend to explode
under certain conditions. Appropriate protective measures (safety
glasses, face shields, leather coat, ear plugs and earthing equip-
ment and person) should be taken during the synthesis, test and
measurement processes, especially when these compounds are
prepared on a larger scale.
The thermal stabilities of the related compounds were
studied by differential scanning calorimetry (DSC) at a heating
rate of 10 1C minꢀ1 (Fig. 11 and 12). For 1 and 4, no amino
groups inside, they all have a melting point, but for 2, 3, 5 and
6, substituents including either 1 or 2 amino groups inside,
there are only exotherm peaks. All of the derivatives decom-
posed between 250 and 350 1C, and their thermal stability
decreased as the number of amino groups increased, this is
Materials and instruments
unexpected as the substituted combination of amino and nitro The starting materials used in the present study were of AR
groups can stabilize the molecule. grade and purchased from the trade. 2,4-Dinitroimidazole
Overall, based upon their performance parameters, these (2,4-DNI) was prepared from commercially available 4-nitroimid-
compounds are especially promising candidates for energetic azole with the total yield of 83% by following the method of Cho
materials and are all thermally stable, since they all decom- et al.,5 and 4,5-dinitroimidazole (4,5-DNI) was obtained by nitra-
posed at high temperatures.
tion of 4-nitroimidazole with the yield of 75%.20 Picryl chloride (a),
c
2842 New J. Chem., 2013, 37, 2837--2844
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3-chloro-2,4,6-trinitro-benzenamine (b) and 5-chloro-1,3-diamino-
2,4,6-trinitrobenzene (c) were obtained according to ref. 1. Melting
point was measured on a X-4 melting point apparatus and was
1
uncorrected. H NMR (500 MHz) and 13C NMR (125 MHz) were
recorded on a Bruker Avance Spectrometer (TMS as an internal
standard). High-resolution mass spectra were recorded on a
Finnigan TSQ Quantum ultra AM mass spectrometer. Elemental
analysis was carried out on a Perkin-Elmer instrument.
The synthesis of the starting compounds (Scheme 1)
2,4-Dinitroimidazole (2,4-DNI). Yield: 82%; m.p. 264–266 1C;
1H NMR (DMSO-d6): d 8.46 (s, 1H).
4,5-Dinitroimidazole (4,5-DNI). Yield: 72%; m.p. 187–189 1C
1
(188–189 1C20); H NMR (DMSO-d6): d 7.97 (s, 1H).
Picryl chloride (a). Yield: 72%; m.p. 80–82 1C; 1H NMR
(CDCl3): d 8.87 (s, 1H).
3-Chloro-2,4,6-trinitro-benzenamine (b). Yield: 76%; m.p.
1
184–185 1C; H NMR (DMSO-d6): d 8.96 (s, 1H), 8.57 (s, 2H).
5-Chloro-1,3-diamino-2,4,6-trinitrobenzene (c). Yield: 40%;
1
m.p. 250–253 1C; H NMR (DMSO-d6): d 8.60 (s, 1H).
Scheme 2 Synthesis scheme of dinitroimidazole derivatives.
A general procedure for the preparation of
N-aryl-C-nitroimidazoles (Scheme 2)
1-(3-Amino-2,4,6-trinitrophenyl)-2,4-dinitroimidazole (2). Yield:
50%; m.p. 260–263 1C; 1H NMR (DMSO-d6): d 8.92 (s, 2H),
9.12 (s, 1H), 9.16 (s, 1H); 13C NMR (DMSO-d6): d 125.45,
126.39, 127.14 127.50 127.78, 128.42, 132.46, 135.19, 140.84,
141.14, 143.60; anal. calcd for C9H4N8O10: C, 28.14; H, 1.05;
N, 29.17%; found: C, 28.22; H, 1.08; N, 29.21%. MS (ESI) m/z:
382.84 (M-H).
1-(3,5-Diamino-2,4,6-trinitrophenyl)-2,4-dinitro-imidazole (3).
Yield: 78%; m.p. 251–253 1C; 1H NMR (DMSO-d6): d 8.40 (s, 4H),
9.10 (s, 1H). 13C NMR (DMSO-d6) d: 121.60, 121.91, 124.76,
126.44, 129.31, 141.58, 143.35; anal. calcd for C9H5N9O10: C,
27.08; H, 1.26; N, 31.58%; found: C, 27.11; H, 1.31; N, 31.62%.
MS (ESI) m/z: 397.81 (M-H).
A mixture of dinitroimidazole (2,4-DNI or 4,5-DNI, 0.32 g,
2.02 mmol), KHCO3 (0.2 g, 2 mmol) and isopropanol (20 mL)
was stirred at ambient temperature for 1 h, followed by TBAB
(tetrabutyl ammonium bromide, 0.12 g, 0.38 mmol), then chloro-
nitroarene (a, b, c, 2 mmol) was added in small lots with stirring.
The contents were stirred for 24 h at 85 1C The reaction mixture
was filtrated and washed with water and then methanol to yield
pure products:
1-(2,4,6-Trinitrophenyl)-2,4-dinitroimidazole (1). Yield: 57%;
m.p. 238–241 1C (237–240 1C12); 1H NMR (DMSO-d6): d 9.06
(s, 2H), 8.99 (s, 1H).
1-(2,4,6-Trinitrophenyl)-4,5-dinitroimidazole (4). Yield: 65%;
m.p. 226–229 1C (220–223 1C12); 1H NMR (DMSO-d6): d 9.38
(s, 2H), 8.59 (s, 1H).
1-(3-Amino-2,4,6-trinitrophenyl)-4,5-dinitro-imidazole (5). Yield:
61%; m.p. 282–284 1C; 1H NMR (DMSO-d6): d 8.57 (s, 1H), 8.92
(s, 2H), 9.15 (s, 1H); 13C NMR (DMSO-d6): d 125.52, 126.17,
127.56, 129.09, 130.53, 132.56, 136.44, 138.44, 140.93; anal.
calcd for C9H4N8O10: C, 28.14; H, 1.05; N, 29.17%; found: C,
28.22; H, 1.08; N, 29.21%. MS (ESI) m/z: 382.84 (M-H).
1-(3,5-Diamino-2,4,6-trinitrophenyl)-4,5-dinitro-imidazole (6).
Yield: 84%; m.p. 271–274 1C; 1H NMR (DMSO-d6): d 8.35 (s, 4H),
8.55 (s, 1H). 13C NMR (DMSO-d6) d 1221.81, 122.73, 127.17,
131.16, 136.07, 137.91, 140.69, 141.47, 146.18; anal. calcd for
C9H5N9O10: C, 27.08; H, 1.26; N, 31.58%; found: C, 27.11; H,
1.31; N, 31.62%. MS (ESI) m/z: 397.79 (M-H).
Acknowledgements
We gratefully acknowledge the financial support from Nanjing
University of Science and Technology.
Scheme 1 Synthesis scheme of reagents and substrates.
c
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Paper
NJC
14 X. Li, R. Zhang and X. Zhang, J. Hazard. Mater., 2010,
183, 622.
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