Energetic C-trinitromethyl-substituted pyrazoles: Synthesis and characterization

Article abstract of DOI:10.1039/c8dt04712j

A new family of C-trinitromethyl-substituted pyrazoles was designed and obtained in good yields by the reaction of N₂O₄ with the pyrazolecarbaldehyde oxime followed by further N-nitration and C-nitration. All of the new compounds were fully characterized by IR and NMR spectroscopy, elemental analysis and differential scanning calorimetry (DSC). Compounds 2 and 3 were further confirmed by X-ray crystallography. These pyrazole derivatives have good densities, positive enthalpies of formation and acceptable sensitivity values. Theoretical calculations carried out using Gaussian 03 and EXPLO5 program demonstrate good to excellent detonation velocities and pressures in the range of ADN and HMX. Compound 3 exhibiting a positive oxygen balance, high specific impulse and moderate thermal stability is a promising high energy density oxidizer.

Full text of DOI:10.1039/c8dt04712j

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Energetic C-trinitromethyl-substituted pyrazoles:
synthesis and characterization†
Cite this: DOI: 10.1039/c8dt04712j
a
a
a
a
b
Yiying Zhang,
Siping Pang
Yanan Li,
Jianjian Hu, Zhongxue Ge, Chenghui Sun * and
b
*
A new family of C-trinitromethyl-substituted pyrazoles was designed and obtained in good yields by the
reaction of N with the pyrazolecarbaldehyde oxime followed by further N-nitration and C-nitration.
2
O
4
All of the new compounds were fully characterized by IR and NMR spectroscopy, elemental analysis and
differential scanning calorimetry (DSC). Compounds 2 and 3 were further confirmed by X-ray crystallogra-
phy. These pyrazole derivatives have good densities, positive enthalpies of formation and acceptable sen-
sitivity values. Theoretical calculations carried out using Gaussian 03 and EXPLO5 program demonstrate
good to excellent detonation velocities and pressures in the range of ADN and HMX. Compound 3 exhi-
biting a positive oxygen balance, high specific impulse and moderate thermal stability is a promising high
energy density oxidizer.
Received 29th November 2018,
Accepted 27th December 2018
DOI: 10.1039/c8dt04712j
rsc.li/dalton
with an opportunity for further functionalizations. In recent
years, many nitropyrazole derivatives have been designed and
Introduction
The synthesis of novel energetic materials with improved per- synthesized as promising energetic materials (Fig. 1), such as
4
4
formance and decreased sensitivity continues to be the cease- 3,4-dinitropyrazole, 3,5-dinitropyrazole, 4-amino-3,5-dinitro-
1
5
6
less pursuit of researchers. In recent years, polynitro-function- pyrazole, 3,4,5-trinitropyrazole and 3,4,5-trinitro-1-(nitro-
alized heterocycles have become an intense research area in methyl)-1H-pyrazole. Moreover, significant work has been
7
the development of high performance energetic materials with directed toward their preparation, theoretical calculations,
not only excellent detonation properties, high densities and thermal behavior, reactivity, and applications.
positive oxygen balances, but also good thermal stabilities and
Among the nitro-based moieties, the trinitromethyl group
2
insensitivities to impact and friction. The introduction of has the highest oxygen content, and its introduction to a mole-
nitro groups via C- and N-functionalization tends to improve cule is essentially equivalent to adding two nitro groups (since
the densities and overall energetic performance of molecules. one of the nitro groups is necessary for the complete oxidation
Therefore, design of polynitro-functionalized compounds is of the carbon atom in the methyl group). The incorporation of
one of the most attractive tasks in the pursuit of ideal ener- trinitromethyl groups into heterocycles is of interest to
getic materials, while seeking rational introduction methods energetic materials industries for increasing the OB so as to
of nitro groups plays a significant role in the synthesis of these improve the detonation performance. Typically, the well-
important compounds.
known preparation methods of trinitromethyl-substituted
Pyrazole ring has been frequently chosen as the fundamen- compounds involve condensation of the amino derivative with
tal component of energetic molecular structure for possessing trinitroethanol and destructive nitration of a methylene active
large enthalpy of formation, high density and achieving posi- compound
including
RCH
2
C(O)Me,
2 2
RCH CH C(O)Me,
3
8
tive oxygen balance easily. At the same time, the three cate- RCH COOH, and so on. Trinitromethyl functionalized pyr-
2
nated carbon atoms in pyrazole not only enhance thermal azoles are expected to be excellent energetic materials with
stability and impact insensitivity, but also endow the backbone high densities and promising detonation properties. Recently,
several pyrazole derivatives bearing trinitromethyl groups in
a
Xi’an Modern Chemistry Research Institute, Xi’an 710065, China
b
School of Materials Science & Engineering, Beijing Institute of Technology,
Beijing 100081, China. E-mail: sunch@bit.edu.cn, pangsp@bit.edu.cn;
Tel: +86-010-68918049, +86-010-68913038
†
Electronic supplementary information (ESI) available. CCDC 1814221 and
878156. For ESI and crystallographic data in CIF or other electronic format see
1
DOI: 10.1039/c8dt04712j
Fig. 1 Examples of polynitropyrazole derivatives.
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nitration by fuming nitric acid and oleum to give 4-nitro-3-
trinitromethylpyrazole (3). It was found that reducing of reac-
tion temperature from 80 °C to room temperature was favor-
able to improve yield to 68% with the reaction time of 2 hours.
Additionally, the same treatment on 2 also led to giving 3,
illustrating that the N–NO
process. Similar to compound 1, 3 was also attempted to react
2
was removed in the nitration
Fig. 2 Representative pyrazole derivatives bearing trinitromethyl
groups as oxygen-rich high performance energetic materials.
with N O , but the desired N-nitration did not happen
2
4
(
Scheme 1).
Single crystals of 2 and 3 suitable for single-crystal XRD
the N position have been synthesized as oxygen-rich high
performance energetic materials (Fig. 2). For example,
N-trinitroethylamino pyrazoles were synthesized by Shreeve
et al. through Mannich reactions between N-amino nitropyra-
were obtained by the slow evaporation of dichloromethane
and petroleum ether solutions of these compounds at room
temperature. The crystals were stable at room temperature and
were found not to be hygroscopic. Their molecular structures
are shown in Fig. 3–4.
9
zoles and trinitroethanol. Later N-trinitromethyl nitropyra-
zoles were synthesized by destructive nitration of the corres-
1
0
Compound 2 crystallizes in the monoclinic space group
ponding N-acetonylpyrazoles. However, to the best of our
knowledge, the preparation of C-trinitromethyl-substituted
pyrazoles which may also hold considerable energetic pro-
perties has not yet been reported.
P2 /c with four molecules per unit cell and has a calculated
1
density of 1.886 g cm− at 153 K (Fig. 3). The C2–C3, C3–C4,
3
C4–N5, C2–N4 and N4–N5 bond lengths are 1.409, 1.371,
1
.357, 1.337 and 1.340 Å, respectively, which are in the normal
In our continuing search for new high-performance poly-
nitro energetic materials, we are interested in developing novel
trinitromethyl-substituted heterocyclic compounds. Herein,
the C-trinitromethyl-substituted pyrazole was first synthesized
1
1
range. The bond length of N5–N6 is 1.442 Å, which corres-
ponds to a N–N single bond. The bond lengths of C1–N1, C1–
N2 and C1–N3 in the trinitromethyl group are 1.545, 1.528 and
2 4
by the reaction of N O with 3-pyrazolecarbaldehyde oxime.
Afterwards, 3-trinitromethylpyrazole was subsequently nitrated
in N and C positions respectively by different nitration systems
to increase energetic performance. Each of these compounds
was fully characterized and their energetic properties were
determined either empirically or theoretically.
Results and discussion
As was stated in the introduction, the introduction of trinitro-
methyl group in the C atom of pyrazole was first attempted
through the reaction of N O with 3-pyrazolecarbaldehyde
2 4
Scheme 1 The synthesis route of 1, 2 and 3.
oxime. The 3-pyrazolecarbaldehyde oxime was chosen in the
consideration of the possible further nitration on other C
atoms after the successful conversion of the formaldoxime
into trinitromethyl group. The raw material 3-pyrazolecarb-
aldehyde oxime was readily synthesized by treatment of
hydroxylamine hydrochloride with 3-pyrazolecarbaldehyde.
Reaction of 3-pyrazolecarbaldehyde oxime with N O resulted
2 4
in two main products: the desired 3-trinitromethylpyrazole (1)
and the unexpected 1-nitro-3-trinitromethylpyrazole (2). It was
found that increasing the N
2 4
O
concentration (within the Fig. 3 Left: Molecular structure of 2; Right: packing diagram of 2.
range of 0.5–2.0 mL N O per mmol 3-pyrazolecarbaldehyde
2
4
oxime) increased the relative proportion of 2 in the product
mixture. Pure compound 1 reacted with N in acetonitrile
2 4
O
also afforded compound 2 in a moderate yield. These
evidences proved that compound 1 was an intermediate in the
formation of compound 2 and N O was able to nitrate
2 4
pyrazole in the N position which has not yet been reported in
previous literatures as far as we know.
After the successful introduction of trinitromethyl into
pyrazole ring, compound 1 was continuously subjected to Fig. 4 Left: Molecular structure of 3; Right: packing diagram of 3.
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1
.532 Å, respectively, all of which are longer than a standard considered the bulky trinitromethyl group has a negative effect
1
2
C–N single bond (1.460 Å). The nitro group bonded to the on crystal packing, so the trinitromethyl-substituted com-
pyrazole is twisted out of the pyrazole plane based on the pounds are not inclined to obtain high densities. For example,
O7–N6–N5–C4 torsion angle (−7.121°) and O8–N6–N5–N4 compound 1 holds a lower density (1.64 g cm− ) compared
3
torsion angle (−8.541°).
with other polynitro pyrazole derivatives with close oxygen
Compound 3 crystallizes in a monoclinic crystal system balance such as 1,3-dinitropyrazole and 3,4-dinitropyrazole.
−
3
with space group P2
1
/n and a density of 1.840 g cm at 153 K Introduction of another nitro group into 1 resulted in the for-
(Fig. 4). The bond lengths and bond angles in the pyrazole mation of 2 and 3, accompanied with the increase of density,
ring of this compound are in the typical ranges. The C3–N5 and obviously the nitro group in the N position has a signifi-
bond length is 1.421 Å, which is shorter than the normal C–N cantly greater effect than in the C position.
single bond. Similar to 2, the C–N bond lengths in the trinitro-
methyl groups are longer than normal C–N single bonds. Gaussian 03 program package. All compounds exhibit posi-
Compared to 2, the nitro group bonded to the pyrazole and tive enthalpies of formation in the range of 208.1–311.4
The enthalpies of formation were computed based on the
1
3
−
1
the pyrazole ring are twisted relatively to each other more kJ mol , which are more positive than those of AP (−295.8
−1
−1
−1
obviously with the O8–N5–C3–C2 torsion angle (13.00°) and kJ mol ), ADN (−149.8 kJ mol ) as well as RDX (92.6 kJ mol )
O7–N5–C3–C4 torsion angle (12.69°), which is probably caused and HMX (116.1 kJ mol− ). These high positive HOFs for all tri-
by the greater influence from the trinitromethyl group in the nitromethyl pyrazoles derive from the high nitrogen content.
ortho-position. In the packing diagram of 3 there are five Interestingly, compared to compound 1, 2 has a increase in
strong inter (between the activated 1-position protons and HOF of 50.1 kJ mol− while the HOF of isomer 3 decreases in a
nitro groups, 2.09–2.82 Å) molecular hydrogen bonding inter- value of 53.2 kJ mol− . Using the calculated enthalpies of for-
1
1
1
actions around each molecule.
The physicochemical and energetic properties of each of the detonation properties of all the compounds were deter-
mation and the measured densities at ambient temperature,
1
4
the compounds are summarized in Table 1.
mined using the EXPLO5 (v6.01) program. The calculated
In this work, the thermal stabilities of all compounds were detonation velocities (D) and detonation pressures (P) fall in
determined by differential scanning calorimetry (DSC) the range of 8249–8933 m s− and 28.6–35.9 GPa, respectively,
1
−
1
measurements scanning at 5 °C min under dry, oxygen-free which are all significantly superior to those of ADN. Especially,
nitrogen over the temperature range from 25 to 500 °C. The compound 2 surpasses RDX overall in term of detonation
melting points of these trinitromethyl pyrazoles 1–3 range properties.
from 59.9 °C (2) to 147.2 °C (3), while their decomposition
Specific impulse (I ) is an extremely important parameter
sp
temperatures are in the range from 104.1 °C (1) to 154.2 °C (3). which determine the efficiency of a propellant. A propellant
Both 1 and 2 have lower melting points than TNT, while they having a high specific impulse is more efficient as it produces
hold low decomposition temperatures (1, 104.1 °C; 2, more thrust per unit of propellant. The specific impulse values
1
13.0 °C), which can be attributed to the well-known instability of synthesized compounds in this study were calculated under
of the trinitromethyl moiety at higher temperatures. isobaric conditions at 7 MPa with an initial temperature of
Surprisingly, compound 3 has much better thermal stability 3300 K by using EXPLO5 (v6.01). As can be seen from Table 1,
compared to isomer 2 with a decomposition temperature of 2 and 3 have much higher specific impulse values (2, 274 s; 3,
1
54.2 °C, which is comparable to that of ADN (159 °C).
269 s) than AP (157 s) and ADN (202 s).
Density is one of the most important physical properties of
Oxygen balance (OB), which indicates the degree to which
energetic materials. The densities of all the compounds were an explosive can be oxidized, is an important index for identi-
measured using a gas pycnometer at 25 °C, and were found to fying the potential of energetic materials as explosives or oxi-
−
3
be in the range of 1.64 (1) to 1.82 g cm (2). It is generally dants. It can be described as the oxygen excess that a com-
Table 1 Physicochemical and energetic properties of compounds 1, 2 and 3
a
b
c
d
e
f
g
h
i
j
Compd
T
m
T
d
ρ
Δ
f
H
M
D
P
I
sp
IS
FS
OB
1
2
3
70.6
59.9
147.2
204
—
—
93
104.1
113.0
154.2
230
287
>200
159
1.64
261.3
311.4
208.1
92.6
104.8
−295.8
−149.8
8249
8933
8598
8795
9320
6368
7860
28.6
35.9
32.2
34.9
39.6
15.8
23.6
273
274
269
258
—
157
202
18
2.5
3
7.4
7.4
15
>360
36
80
120
120
>360
64–72
3.69
18.3
18.3
0
0
26
k
k
1.82/1.85
1.75/1.80
1.80
1.91
1.95
l
RDX
HMX
AP
ADN
m
n
n
1.81
3–5
26
a
Melting point (onset) [°C]. Decomposition temperature (onset) [°C]. Density measured by a gas pycnometer at 25 °C [g cm−3]. d Calculated
b
c
−
1
e
−1
f
g
h
i
enthalpy of formation [kJ mol ]. Detonation velocity [m s ]. Detonation pressure [GPa]. Specific impulse [s]. Impact sensitivity [J]. Friction
j
sensitivity [N]. Oxygen balance assuming the formation of CO at combustion (for C H O N , OB = 1600(c − a − b/2)/MW, MW = molecular
a b c d
k
−4
T v 0 v
weight of compound.) [%]. Crystal density at 298 K, recalculated from low-temperature X-ray densities, ρ298 K = ρ /(1 + α (298 − T )), α = 1.5 × 10 ,
−3
l
m
n
0
T is the crystal testing temperature [g cm ]. Ref. 15. Ref. 16. Ref. 7.
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pound needs to convert all carbon into carbon monooxide, all USA) over the range of 4000–400 cm− . H NMR and C NMR
1
1
13
hydrogen into water and nitrogen into dinitrogen. Compound spectra were recorded on a Bruker ARX-400 instrument
1
, 2 and 3 all have positive OBs, exceeding that of RDX. (Zurich, Switzerland). Chemical shifts are reported in ppm
Isomers 2 and 3 hold a high OB value of 18.3% which is com- relative to tetramethylsilane. Elemental analyses (C, H and N)
parable to the OBs of AP and ADN. Their combined nitrogen + were performed using an Elementar Vario EL (Bremen,
oxygen contents of 81% are also significantly better compared Germany). Liquid chromatography (LC)-MS electrospray
to AP (65%). These results suggest that compound 3 is quite ionization (ESI) data were acquired with an Agilent 6120
promising high energy density oxidizer with a high oxygen LC-MS spectrometer (Santa Clara, CA, USA). Crystal structures
balance, a thermal stability comparable to ADN and a superior were determined on a Rigaku RAXIS IP diffractometer (Rigaku
specific impulse compared with AP and ADN.
Corporation, Tokyo, Japan) with the SHELXTL crystallographic
The sensitivities of these compounds towards impact (IS) software package of molecular structure. The melting and
and friction (FS) were determined by using a BAM drop decomposition points of the compounds were determined
hammer apparatus and BAM friction tester, respectively. using a TA-DSC Q2000 differential scanning calorimeter (New
Compound 1 (IS = 18 J, FS > 360 N) has impact and friction Castle, DE, USA) at a scanning rate of 5 °C min− . Densities
sensitivities similar to those of TNT. As a result of the intro- were measured at 25 °C using a Micromeritics Accupyc II
duction of a nitro group, 2 (IS = 2.5 J, FS = 36 N) and 3 (IS = 3 J, 1340 gas pycnometer. The impact and friction sensitivity
FS = 80 N) become more sensitive than 1 and RDX (IS = 7 J, measurements were carried out with a BAM fall hammer
1
FS = 120 N), which correspond to sensitive materials.
apparatus (BFH-10) and a BAM friction apparatus (FSKM-10),
respectively.
Theoretical studies
Conclusions
Calculations were performed using the Gaussian 03 suite of
C-Trinitromethyl-substituted pyrazole derivatives including programs. The geometric optimization of the structures and
3
4
-trinitromethylpyrazole, 1-nitro-3-trinitromethylpyrazole and frequency analyses employed the density functional theory
-nitro-3-trinitromethylpyrazole have been synthesized in mod- (DFT) B3LYP method with the 6-311+G** basis set and single-
erate to excellent yields. All the compounds were fully charac- point energies were calculated at the MP2/6-311+G** level.
terized and their energetic properties were both measured and Each optimized structure was characterized to determine the
calculated. They possess excellent detonation properties in the true local energy minima on the potential energy surface
−
1
range of 8249–8933 m s and 28.6–35.9 GPa, respectively, without imaginary frequencies. The heats of formation (ΔHf)
which are all significantly superior to those of ADN (7860 of the neutral molecules were computed using the isodesmic
−
1
17
m s , 23.6 GPa). The oxygen balances of compounds 2 and 3 reaction.
The enthalpy of each isodesmic reaction was
are comparable to those of AP and ADN and their sensitivity obtained by combining the MP2/6-311+G** energy difference
values are in the range of primary explosives. In regard of the for the reaction, the scaled zero point energies (B3LYP/
thermal stability, compound 1 and 2 hold low decomposition 6-311+G**) and other thermal factors (B3LYP/6-311+G**). Using
temperatures (1, 104.1 °C; 2, 113.0 °C) due to the instability of these heats of formation and densities, detonation velocities
the trinitromethyl moiety, however, compound 3 has moder- and detonation pressures were calculated using the EXPLO5
18
ately high thermal stability (T = 154 °C) comparable to that of v6.01 program according to the Kamlet–Jacobs equations.
d
d
ADN (T = 159 °C), which is attributed to the strong inter-
molecular hydrogen bonding interactions. Based on an ideal
combination of detonation property, oxygen balance, specific
3
-Trinitromethylpyrazole (1) and 1-nitro-3-trinitromethylpyrazole
(2)
impulse and thermal stability, compound 3 can serve as a In a three-necked batch reactor equipped with a reflux conden-
promising candidate as a new high energy density oxidizer.
ser, 3-pyrazolecarbaldehyde oxime (0.56 g, 5 mmol) was dis-
solved in acetonitrile (20 mL) at room temperature. N
5 mL) was poured into a container in ice-water bath and then
2 4
O
(
Experimental
added dropwise into the reactor with vigorous stirring. The
reaction mixture was subsequently heated to 60 °C and main-
tained at this temperature for 2 h. Then the mixture was
cooled to room temperature and stirred vigorously to remove
residual N O . The solvent was evaporated under vacuum and
2 4
the residue was purified by column chromatography, using a
Biotage Isolera One apparatus with a Flash Silica-CS column
Caution: Although none of the compounds described herein
exploded or detonated in the course of this research, these
energetic materials should be handled with extreme care using
best safety practices (including the use of personal protective
equipment such as leather gloves, face shield and ear plugs).
(
25 g), eluting with n-hexane and dichloromethane. 0.42 g of
General
pure product 1 as white solid (yield 38.25%) and 0.20 g of pure
All starting materials were commercially available and were product 2 as white solid (14.96%) were isolated, respectively.
used as-received. IR spectra were obtained from KBr pellets 1: R = 0.3 (silica gel, 33% hexanes/dichloromethane); m
using a Nicolet Magna IR 560 spectrophotometer (Madison, 70.6 °C; T = 104.1 °C; H NMR (600 MHz, dmso): δ 8.12 (d,
f
p
=
1
d
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1
3
J = 2.4 Hz, 1H), 7.09 (d, J = 2.4 Hz, 1H); C NMR (151 MHz,
dmso) δ 134.54, 132.26, 110.64, 109.33 ppm; IR (KBr): 3170,
2 (a) V. Thottempudi and J. M. Shreeve, J. Am. Chem. Soc.,
2011, 133, 19982–19992; (b) A. A. Dippold and
T. M. Klapötke, J. Am. Chem. Soc., 2013, 135, 9931–9938;
(c) V. Thottempudi, F. Farhad, D. A. Parrish and
J. M. Shreeve, Angew. Chem., Int. Ed., 2012, 51, 9881–9885.
3 (a) J. Zhang, C. He, D. A. Parrish and J. M. Shreeve, Chem. –
Eur. J., 2013, 19, 8929–8936; (b) C. He, J. Zhang,
D. A. Parrish and J. M. Shreeve, J. Mater. Chem. A, 2013, 1,
2863–2868.
−
1
2
960, 1604, 1593, 1361, 1300, 1219, 1056, 843, 802, 777 cm ;
−
−
MS (ESI) m/z: 216 [M − 1] , 171 [M − 46] ; elemental analysis
for C H N O : calculated C 22.13, H 1.39, N 32.26%; measured
4
3 5 6
C 22.05, H 1.32, N 32.33%.
: R = 0.8 (silica gel, 33% hexanes/dichloromethane); m
9.9 °C; T = 113.0 °C; H NMR (600 MHz, dmso) δ 9.17 (d, J =
2
f
p
=
1
5
3
d
1
3
.1 Hz, 1H), 7.53 (d, J = 3.1 Hz, 1H); C NMR (151 MHz,
dmso) δ 134.93, 129.31, 118.95, 112.37 ppm; IR (KBr): 3144,
4 J. W. A. M. Janssen, H. J. Koeners, C. G. Kruse and
C. L. Habrakern, J. Org. Chem., 1973, 38, 1777–1782.
5 R. D. Schmidt, G. S. Lee, P. F. Pagoria, A. R. Mitchell and
R. Gilardi, J. Heterocycl. Chem., 2001, 38, 1227–1230.
6 G. Herve, C. Roussel and H. Graindorge, Angew. Chem., Int.
Ed., 2010, 122, 3245–3249.
−
1
1
655, 1619, 1596, 1301, 1259, 1135, 1048, 816, 802, 771 cm ;
−
−
MS (ESI) m/z: 261 [M − 1] , 216 [M − 46] ; elemental analysis
for C : calculated C 18.33, H 0.77, N 32.07%; measured
C 18.26, H 1.01, N 32.15%.
4
2 6 8
H N O
3
-Trinitromethyl-4-nitropyrazole (3)
7 D. Kumar, G. H. Imler, D. A. Parrish and J. M. Shreeve,
J. Mater. Chem. A, 2017, 5, 10437–10441.
3
-Trinitromethylpyrazole (1) (1.09 g, 5 mmol) was added to a
8
(a) I. V. Ovchinnikov, A. S. Kulikov, M. A. Epishina,
N. N. Makhova and V. A. Tartakovsky, Russ. Chem. Bull.,
3
mixture of fuming HNO (6 mL) and oleum (4 mL), with stir-
ring and cooling in an ice bath. Then the reaction mixture was
stirred at room temperature. After 2 hours, the reaction
mixture was poured into cold water and extracted with ethyl
acetate. The organic solution was dried over anhydrous
2
005, 54, 1346–1349; (b) T. P. Kofman, G. Y. Kartseva,
E. Y. Glazkova and K. N. Krasnov, Russ. J. Org. Chem., 2005,
1, 753–757.
4
9
P. Yin, J. Zhang, C. He, D. A. Parrish and J. M. Shreeve,
MgSO . The solvent was evaporated under vacuum and the
4
J. Mater. Chem. A, 2014, 2, 3200–3208.
residue was purified by column chromatography on a Biotage
Isolera One apparatus using a Flash Silica-CS column (25 g)
and eluting with ethyl acetate and n-hexane. The product 3
1
0 I. L. Dalinger, I. A. Vatsadze, T. K. Shkineva,
A. V. Kormanov, M. I. Struchkova, K. Y. Suponitsky,
A. A. Bragin, K. A. Monogarov, V. P. Sinditskii and
A. B. Sheremetev, Chem. – Asian J., 2015, 10, 1987–1996.
was isolated with satisfactory purity as a white solid (0.89 g,
1
6
7.63%). m
p
= 147.2 °C; T
d
= 154.2 °C; H NMR (600 MHz,
1
3
11 Y. Zhang, D. A. Parrish and J. M. Shreeve, J. Mater. Chem.,
012, 22, 12659–12665.
dmso) δ 9.45 (s, 1H); C NMR (151 MHz, dmso) δ 134.59,
1
1
MS (ESI) m/z: 261 [M − 1] , 216 [M − 46] ; elemental analysis
for C : calculated C 18.33, H 0.77, N 32.07%; measured
C 18.23, H 1.03, N 32.12%.
2
33.93, 130.37, 124.63 ppm; IR (KBr): 3253, 3142, 1610, 1588,
−
1
12 Q. Yu, Z. Wang, B. Wu, H. Yang, X. Ju, C. Lu and G. Cheng,
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Conflicts of interest
There are no conflicts to declare.
Acknowledgements
The authors acknowledge financial support from the National
Natural Science Foundation of China (21576026 and U153062).
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