Preparation, Characterization, and Molecular Structure of Two New Heat-Resistant Energetic Compounds

Article abstract of DOI:10.1080/15421406.2015.1011457

In this paper, nitration of 2,2'-diphenic acid was studied and two aromatic carboxylic acids containing two and four nitro groups, respectively, were synthesized and characterized through elemental analysis, IR spectra, respectively. Crystal structure of 4,4'-dinitro-2,2'-diphenic acid and 4,4',6,6'-tetranitro-2,2'-diphenic acid was determined by X-ray single crystal diffraction and their thermal decomposition have been carried out through differential scanning calorimeter analyses at a heating rate of 10°C/min. The results indicate that the compounds have high heat-resistant stability.

Full text of DOI:10.1080/15421406.2015.1011457

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Preparation, Characterization, and Molecular
Structure of Two New Heat-Resistant Energetic
Compounds
F. F. Chang, J. R. Zhang & R. F. Wu
To cite this article: F. F. Chang, J. R. Zhang & R. F. Wu (2015) Preparation, Characterization, and
Molecular Structure of Two New Heat-Resistant Energetic Compounds, Molecular Crystals and
Liquid Crystals, 623:1, 275-284, DOI: 10.1080/15421406.2015.1011457
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Date: 02 April 2016, At: 06:43

Mol. Cryst. Liq. Cryst., Vol. 623: pp. 275–284, 2015
Copyright © Inner Mongolia University of Technology
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2015.1011457
Preparation, Characterization, and Molecular
Structure of Two New Heat-Resistant Energetic
Compounds
∗
F. F. CHANG, J. R. ZHANG, AND R. F. WU
Chemical Engineering College, Inner Mongolia University of Technology,
Hohhot, China
ꢀ
In this paper, nitration of 2,2 -diphenic acid was studied and two aromatic carboxylic
acids containing two and four nitro groups, respectively, were synthesized and charac-
ꢀ
terized through elemental analysis, IR spectra, respectively. Crystal structure of 4,4 -
ꢀ
ꢀ
ꢀ
ꢀ
dinitro-2,2 -diphenic acid and 4,4 ,6,6 -tetranitro-2,2 -diphenic acid was determined by
X-ray single crystal diffraction and their thermal decomposition have been carried out
through differential scanning calorimeter analyses at a heating rate of 10 C/min. The
◦
results indicate that the compounds have high heat-resistant stability.
Keywords Energetic compounds; molecular structure; thermal stability
Introduction
The nitration of deactivated aromatic compounds is an important reaction and plays a key
role in the synthesis of medicines, pesticides, dyes, and explosives [1]. The DPA is a very
good electron pair donor for two carboxyl groups, so it can be designed to assemble many
novel metal-organic coordinate polymer materials (MOCP) with transition metal [2–5].
In order to explore the newly MOCP containing nitro groups for potential applications
as heat-resistant energetic material, we decorated DPA by bringing more nitro groups to
ꢀ
the aryl ring. In our previous study, nitration of 4,4 -biphenyl dicarboxylic acid have been
reported [6, 7].
Herein, we report the nitration of DPA with high concentration sulfuric and nitric acids.
The title molecules DNDPA and TNDPA containing two and four nitryls and two phenyls
respectively, so their heating restrained stability and solubility will be improved so that
they can be used as heating restrained energetic compounds and organic energetic ligands
of MOCP materials.
In this work, we cultured single crystals of the two compounds in DMF. The molecular
and crystal structures were determined by X-ray single-crystal diffraction analysis. The
thermal decomposition processes of the compounds were investigated to examine their
thermal stability.
∗
Address correspondence to R. F. Wu, Chemical Engineering College of Inner Mongolia
University of Technology, Aimin Street No. 49, District of Xincheng, Hohhot, 010051, China.
E-mail: rfwu02@imut.edu.cn
275

276
F. F. Chang et al.
Experimental, Material, and Measurement
All analytical grade chemicals and solvents were purchased commercially and used without
further purification. Elemental analysis was carried out on Carlo Erba 1106 full-automatic
trace organic elemental analyzer. FT-IR spectra were recorded with a Bruker Equinox 55
−1
FT-IR spectrometer in dry KBr pellet in the range of 400–4000 cm . A perkin-Elmer
Pyris-1 differential scanning calorimeter (DSC) was used for DSC measurement (sample
mass: about 1.0 mg, atmosphere: flowing nitrogen gas, reference sample: α-Al2O3, heating
◦
rate: 10 C/min).
X-Ray Crystallography
The data collections were performed on Rigaku AFC-10/Saturn 724 + CCD detector
diffractometer equipped with a graphite-monochromatic MoK/α radiation (λ = 0.71073Å)
at 153(2)K by using the ω scans with a multiscan mode. The structure was solved by direct
methods using SHELXS-97 program [8] and refined by full-matrix least-squares methods
on F2 with SHELXL-97 program [9].
Synthesis of DPA
Synthesis of DPA followed the literature [10]. A solution of phenanthrene (9 g) in 20 mL
◦
pyridine was stirred with 30 g potassium permanganate at 70 C and lasted half an hour. Then
30 mL sodium hydroxide was added into the solution and the reaction was continuously
stirred until the purple disappeared completely. An amount of 50 mL distilled water was
mixed into the solution when it was cooled. The pyridine was steamed out from the solution.
The filtrate was acidified with hydrochloric acid and 7 g white crystal product obtained by
◦
filtration, the yield was 70%. mp: 231–232 C.
Synthesis of DNDPA
An amount of 12.1 g of DPA was dissolved in 75 mL of concentrated sulfuric acid and
◦
2
5 mL fuming nitric acid was added into the solution keeping the temperature below 50 C.
◦
After addition, the solution was stirred continuously for 10 min, quickly heated to 60 C and
then kept at this temperature for 2 hr. Consequently, the reaction mixture was poured into
a little crushed ice. After several hours, the slightly yellow solid was collected on a filter,
washed and dried at 60 C and 14.2 g of DNBPDC was obtained. mp: 236 C (decomposed).
The product is insoluble in ether, chloroform, and cold water, but soluble in alcohol and
DMF. When the material was recrystallized from DMF at high temperature, very fine
needles were obtained. Anal. Calcd. (%) for C16H15N3O8: C, 50.93; H, 4.01; N, 11.14.
◦
◦
−1
Found (%): C, 50.90; H, 3.99 N, 11.05. IR: νas (CO2–) 1709(s) cm , νs (NO2)1344 (s)
−1
−1
cm , and νas (NO2) 1533(m) cm .
Synthesis of TNDPA
A solution of 16.6 g of DNDPA in 25 mL of fuming sulfuric acid was stirred and treated
◦
keeping the temperature bellowing 50 C with 8.4 mL fuming nitric acid. After the nitric
acid has been added, the cooling bath was removed and the reaction mixture which is
◦
stirred continuously is allowed to warm to 90 C slowly. At the end of two hours, the clear
solution is diluted with 40 g of ice and 40 mL of water and left in the ice box overnight.

Preparation, Characterization, and Molecular Structure
277
By dissolving the crude product in hot water and cooling to room temperature, 18.8 g of
◦
◦
TNBPDC was obtained after drying at 60 C. mp: 294 C (decomposed). When the product
was recrystallized from DMF, very fine pale yellow needles were obtained. Anal. Calcd.
(
%) for C14H6N4O12: C, 39.83; H, 1.43; N, 13.27. Found (%): C, 39.81; H, 1.42; N, 13.23.
−1
−1
−1
IR: νas (CO2–) 1716(s) cm , νs (NO2)1345 (s) cm , and νas(NO2) 1535(m) cm .
Results and Discussion
Synthesis
The scheme 1 shows the equation of the synthesis of DNDPA and TNDPA. Similar to the
synthesis of DNBPDC and TNBPDC [6, 7], DPA was subjected to a nitration reaction in
the presence of mix acid [e.g., concentrated sulfuric acid and fuming nitric acid (DNDPA)
or fuming sulfuric acid and fuming nitric acid (TNDPA)]. DPA nitration by mixed acid
is a heterogeneous liquid–liquid reaction, which occurs almost exclusively in the aqueous
phase. The organic compound diffuses into the aqueous mixed-acid-phase and reacts with
the nitronium ion generated by the reaction between concentrated sulfuric acid and nitric
acid.
Scheme 1. Procedure of preparing the two title compounds.
The crystal of DNDPA was obtained from DMF solution at high temperature, so the
formyl group was removed from DMF molecule to form dimethylamine molecules, which
coexist with DNDPA molecules in the unit cell.
Crystal Structure
The X-ray single-crystal structures of DNDPA and TNDPA were determined. The crystal-
lographic data of the title compounds are listed in Table 1.

278
F. F. Chang et al.
Table 1. Crystallographic data and structure refinement summary for the DNDPA and
TNDPA
Compound
DNDPA
TNDPA
Empirical formula
Formula mass
Color, habit
Crystal dimensions (mm)
Crystal system
Space group
Z
C16 H15 N3 O8
377.31
Pale yellow, needle
0.36 × 0.34 × 0.10
Monoclinic
P2(1)/c
C14 H6 N4 O12
422.23
Pale yellow, needle
0.19 × 0.16 × 0.11
Monoclinic
P2(1)/n
8
4
a (Å)
7.559(2)
11.704(5)
b (Å)
10.228(3)
9.149(3)
c (Å)
β ( )
44.390(13)
90.506(4)
17.083(5)
116.69 (2)
◦
Collection ranges
−8 ≤ h ≤ −8; −12 ≤ k ≤ −13 ≤h ≤ 13; −10 ≤ k ≤
−
12; −51 ≤ l ≤52
10; −11 ≤ l ≤ 20
153(2)
Temperature (K)
153(2)
3
Volume (Å )
Dcalcd (Mg/m )
3431.8 (16)
1.461
1634.3(10)
3
1.716
Radiation
MoKα (λ = 0.71073 Å)
MoKα (λ = 0.71073 Å)
Absorption coefficient
0.119
0.155
−
1
(
mm )
Absorption correction
F(000)
θ range for data collection ( )
Observed reflections
Multiscan
1568
2.04–25.00
17,503
Multiscan
856
2.50–25.00
8,052
◦
Independent eflections/Rint
Data/restraints/parameters
Goodness-of-fit on F2
5,800/0.0561
5,800/30/491
1.118
2,839/0.0448
2,839/0/271
1.059
Final R indices [I > 2σ(I)]
R indices (all data)
0.1299/0.3164
0.1467/0.3264
0.586 and −0.577
0.0502/0.1091
0.0655/0.1191
0.244 and −0.302
Largest diff. peak and hole
−
3
(
e·Å )
DNDPA
ꢀ
ꢀ
As shown in Fig. 1, the unit cell contains two independent 4,4 -dinitro-2,2 -diphenic acid
molecules and two dimethylamine molecules, which is similar to the molecule DPA [11] and
DNBPDA [6]. The bond lengths and bond angles of two DNDPA molecules are different.
A comparison of two DNDPA molecules reveals that the largest difference in distance is
0
.025 Å, C(6)-C(7) and C(20)-C(21). Owing to the steric hindrance effect, the two aryl
◦
rings of the DNDPA are distorted with the torsion angle C(5)-C(6)-C(7)-C(8) of 49.36 and
C(19)-C(20)-C(21)-C(22) of 46.81 . The planes of four carboxyl groups are also distorted
◦
◦
with the aryl rings (torsion angle C(4)-C(5)-C(13)-O(4) = −155.4(8) ; C(7)-C(8)-C(14)-
◦
◦
O(6) = −145.7(7) ; C(23)-C(22)-C(28)-O(13) = −146.1(8) ; and C(18)-C(19)-C(27)-
◦
O(12) = −142.7(7) ). One carboxyl group of each DNDPA molecules is deprotonated by
dimethylamine molecules.

Preparation, Characterization, and Molecular Structure
279
Figure 1. Molecular structure of the DNDPA.
◦
Table 2. Select bond lengths/Å and bond angles/ for the compound DNDPA
◦
Dist
Angle
( )
O(1)-N(1)
O(2)-N(1)
O(3)-C(13)
O(4)-C(13)
O(5)-C(14)
O(6)-C(14)
O(7)-N(2)
O(8)-N(2)
1.223(10)
1.209(10)
1.322(8)
1.190(8)
1.230(8)
1.263(8)
1.196(9)
1.199(9)
O(2)-N(1)-O(1)
O(7)-N(2)-O(8)
123.8(7)
120.7(7)
124.3(6)
125.9(6)
122.2(7)
124.0(7)
126.9(6)
123.5(6)
O(4)-C(13)-O(3)
O(5)-C(14)-O(6)
O(10)-N(3)-O(9)
O(15)-N(4)-O(16)
O(12)-C(27)-O(11)
O(13)-C(28)-O(14)
◦
Table 3. Hydrogen bond lengths (Å) and angles ( ) for DNDPA
No.
Donor–H . . . Acceptor
D–H
H . . . A
D . . . A
D–H . . . A
1
2
3
4
5
6
7
N(6)-H(6B) . . . O(5)#1
N(6)-H(6A) . . . O(11)#2
N(5)-H(5B) . . . O(12)
N(5)-H(5A) . . . O(4)#1
N(5)-H(5A) . . . O(6)#1
O(14)-H(14O) . . . O(6)#3
O(3)-H(3O) . . . O(11)#4
0.92
0.92
0.92
0.92
0.92
0.84
0.84
1.85
1.92
1.88
2.57
1.95
1.74
1.76
2.738(7)
2.778(8)
2.745(7)
3.073(7)
2.785(8)
2.518(7)
2.540(7)
160.3
155.2
154.9
115.3
150.6
152.2
154.0
Symmetry codes: #1: x,y+1,z; #2: x-1,y,z; #3: x+1,y+1,z; #4: x,y-1,z.

280
F. F. Chang et al.
Figure 2. Crystal packing of the DNDPA.
Three nitro groups (1-NO2, 2-NO2, and 3-NO2) were split into two parts with 0.5
occupancy for obtaining good thermal parameters. The planes of these NO2 groups are
distorted with the aryl ring. However, the 4-NO2 group is closely coplanar with the aryl
ring. The N O bond lengths in nitro groups are around the normal N O double bond in
nitro group (about 1.200 Å) (Table 2) [12]. The C O bond lengths of carboxyl groups
varied from 1.200(9) Å to 1.262(9) Å. However, the C O (H) bond lengths of carboxyl
groups change from 1.323(9) Å to 1.331(9) Å, which is evidently shorter than that of the
free carboxyl groups (1.41–1.44 Å).
In the molecule DNDPA, two aryl rings of biphenyl which come from two molecules
stack offset face-to-face in infinite columns along a which are linked into layers and the
◦
distance of two planes is 3.611 Å (θ = 20.53 ), which is in the range of π–π stack-
ing interaction (3.3–3.7 Å) [12]. So there are existence of π–π stacking interaction that
benefits for the formation and stability of the crystals. These layers are held together via
Figure 3. Molecular structure of the TNDPA.

Preparation, Characterization, and Molecular Structure
281
◦
Table 4. Select bond lengths/Å and bond angles/ for the compound TNDPA
◦
Dist
Bond
Dist
Angle
( )
O(1)-C(1)
O(2)-C(1)
O(11)-C(14)
O(12)-C(14)
O(3)-N(1)
O(4)-N(1)
1.228(3)
1.299(3)
1.294(3)
1.234(3)
1.222(3)
1.223(3)
O(5)-N(2)
O(6)-N(2)
O(7)-N(3)
O(8)-N(3)
O(9)-N(4)
O(10)-N(4)
1.225(3)
1.216(3)
1.215(3)
1.221(3)
1.216(3)
1.220(3)
O(3)-N(1)-O(4)
O(6)-N(2)-O(5)
O(7)-N(3)-O(8)
O(9)-N(4)-O(10)
O(1)-C(1)-O(2)
O(12)-C(14)-O(11)
124.5(2)
125.0(2)
124.2(2)
124.3(2)
124.6(2)
125.0(2)
intermolecular hydrogen bonds. The nitrogen atoms of two dimethylamine molecules [N(6)
and N(5)] are involved in an intricate hydrogen bonding network as well as the oxygen
atoms [O(5), O(11), O(12), O(4), and O(6)] of carboxyl group (Table 3). In particular,
the strongest hydrogen bonding interactions are O(14) and O(3) [carboxyl oxygen atoms:
O(14) . . . O(6)#3 2.518(7) Å(#3 x+1,y+1,z); O(3) . . . O(11)#4 2.540(7) Å(#4 x,y−1,z)].
Thus a 2D infinite layer structure is formed through π–π stacking interaction along a
direction and intermolecular hydrogen bonds alone c direction (Fig. 2).
TNDPA
ꢀ
ꢀ
ꢀ
The building unit of the TNDPA is composed of a 4,4 ,6,6 -tetra nitro-2,2 -biphenyl dicar-
boxylic acid molecules (Fig. 3). The two aryl rings of the TNDPA molecule are close to
◦
vertical (the torsion angle: C(2)-C(7)-C(8)-C(9) is 90.48 ). Same as the DNDPA, the car-
boxyl groups of the TNDPA are not coplanar with the aryl rings because of steric hindrance
effect. The C O bond lengths of carboxyl groups varied from 1.228(3) Å to 1.234(3) Å
and the C O (H) bond lengths of carboxyl groups change from 1.294(3) Å to 1.299(3) Å
(
Table 4), which are in the normal range of C O and C O(H) bond lengths of the carboxyl
group [12].
The 4-NO2 and 4 -NO2 are close to coplanar with the aryl rings (torsion angles:
ꢀ
◦
◦
ꢀ
O(10)-N(4)-C(11)-C(10) −178.8(2) ; O(4)-N(1)-C(4)-C(3) 179.6(2) ), but 2-NO2 and 2 -
NO2 are distorted because of steric hindrance effect (torsion angles: O(7)-N(3)-C(9)-C(10)
◦
◦
−
169.7(2) ; O(6)-N(2)-C(6)-C(5) −156.9(2) ).
The TNDPA molecules is linked to a 1D infinite chain structure through two inter-
molecule hydrogen bonds which are formed between a O H group and an oxygen atoms
of carboxyl group (Table 5). As shown in Fig. 3, owing the two aryl rings of biphenyl
are vertical, two adjacent TNDPA molecules staggered arrangement. So two adjacent 1D
arrays are extended to a 2D framework (Fig. 4).
◦
Table 5. Hydrogen bond lengths (Å) and angles ( ) for TNDPA
No.
Donor–H . . . Acceptor
D–H
H . . . A
D . . . A
D–H . . . A
1
2
O(2)-H(2) . . . O(12)#1
O(11)-H(11) . . . O1#2
1.05
1.03
1.55
1.58
2.594(3)
2.592(3)
170.8
167.0
Symmetry codes: #1: -x+1,y+1/2,-z+3/2; #2: -x+1,y-1/2,-z+3/2.

282
F. F. Chang et al.
Figure 4. Crystal packing of the TNDPA.
Thermal Behavior
The DSC curves of the title compounds shown in Figs. 5 and 6, respectively, indicate the
◦
◦
◦
decomposition occurs in the 50 C–600 C range. In Fig. 5, there is one exothermic process
◦
◦
at 20–350 C range with the peak at 239 C and two endothermic process at 320–650 C with
the peak at 373 C and 568 C. In Fig. 6, there is only one aculeate endothermic with the
peak at 331 C. From the result, we find that the compound TNDPA have four nitro groups
◦
◦
◦
in aromatic rings, so initial decomposition temperature of endothermic process is lower
than the compound DNDPA that has two nitro groups. However, the compound DNDPA
◦
and TNDPA both have higher initial decomposition temperatures (above 200 C).
Figure 5. The DSC for DNDPA.

Preparation, Characterization, and Molecular Structure
283
Figure 6. The DSC for TNDPA.
Conclusion
In summary, we have successfully synthesized two aromatic carboxylic acid compounds
containing two and four nitro groups, respectively, by nitration of DPA with mixed sulfuric
and nitric acids. Single crystals of the title compounds were grown using solution growth
technique. X-ray single-crystal analysis revealed that the nitro-substitution of the compound
ꢀ
ꢀ
ꢀ
DNDPA and TNDPA occurs on 4,4 positions and 4,4 ,6,6 positions, respectively. The
structure of the compound DNDPA is a 2D-layered structure by π–π stacking interaction
and intermolecular hydrogen bonds. The compound TNDPA also is a 2D-layered structure
by intermolecular hydrogen bonds. The functional group was confirmed by element analysis
and FT-IR. The thermodynamic analysis result indicates the title compounds have higher
thermal stability although it contain two and four nitryls and can be used as heating
restrained energetic compound or organic energetic ligands of MOCP materials.
Supplementary Data
Crystallographic data for the structures reported in this article have been deposited at the
Cambridge Crystallographic Data Center, CCDC reference number 1016480 and 1016481
for DNDPA and TNDPA, respectively. Copies of the data can be obtained free of charge
from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: t44-1223
336-033; Email: deposit@ccdc.cam.ac.uk).
Funding
This paper was supported by the National Natural Science Foundation of China (21164005)
and the Natural Science Foundation of Inner Mongolia (2010MS0212).
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