Synthesis and characterization of 5-amino-1,3,6-trinitro-1H-benzo[d]imidazol-2(3H)-one as an energetic material

Article abstract of DOI:10.1039/c4ra04796f

Two synthetic routes for the preparation of 5-amino-1,3,6-trinitro-1H-benzo[d]imidazol-2(3H)-one (2) as an energetic material have been revealed. Direct nitration of 5-amino-1H-benzo[d]imidazol-2(3H)-one (1) gave the trinitrated compound 2 in a poor yield of 11%; and similarly using 1 as starting material, 2 was obtained by N-protected reaction, nitration, deprotection and again nitration reaction with an overall-yield of 48%. All structures of 2 and relevant compounds were determined by IR, ¹H NMR, ¹³C NMR spectroscopy, MS and elemental analysis. Theoretical calculations showed that the detonation properties of compound 2 (D = 7.78 km s^-1, P = 27.05 GPa) were satisfactory, compared with 2,4,6-trinitrotoluene (TNT, D = 7.21 km s^-1, P = 22.49 GPa). This journal is

Full text of DOI:10.1039/c4ra04796f

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Synthesis and characterization of 5-amino-1,3,6-
trinitro-1H-benzo[d]imidazol-2(3H)-one as an
energetic material†
Cite this: RSC Adv., 2014, 4, 42215
a
a
ab
*
Congming Ma, Zuliang Liu and Qizheng Yao
Two synthetic routes for the preparation of 5-amino-1,3,6-trinitro-1H-benzo[d]imidazol-2(3H)-one (2) as
an energetic material have been revealed. Direct nitration of 5-amino-1H-benzo[d]imidazol-2(3H)-one
(1) gave the trinitrated compound 2 in a poor yield of 11%; and similarly using 1 as starting material, 2 was
obtained by N-protected reaction, nitration, deprotection and again nitration reaction with an overall-
yield of 48%. All structures of 2 and relevant compounds were determined by IR, 1H NMR, 13C NMR
spectroscopy, MS and elemental analysis. Theoretical calculations showed that the detonation properties
of compound 2 (D ¼ 7.78 km sꢀ1, P ¼ 27.05 GPa) were satisfactory, compared with 2,4,6-trinitrotoluene
(TNT, D ¼ 7.21 km sꢀ1, P ¼ 22.49 GPa).
Received 21st May 2014
Accepted 14th August 2014
DOI: 10.1039/c4ra04796f
www.rsc.org/advances
formation) upon opening of the strained cage or ring system
during decomposition.5–8
Introduction
Nitroureas play an important role in the eld of energetic
materials, and the properties of nitrourea compounds suggest they
would make excellent candidates as both insensitive and highly
energetic materials. In general, both mono- and dinitrourea
derivatives have attractive molecular densities, which has been
attributed to the inherently high density of the urea framework.
However, the dinitrourea explosives suffer from hydrolytic
stability, and thus restricting their use; but the mono-nitrourea
compounds are fairly stable to hydrolysis, mainly due to their
intermolecular hydrogen bonding, and may be candidates as
insensitive energetic materials.9–11 The representative energetic
compounds of nitroureas focus on alicyclic compounds, including
1,3,4,6-tetranitroglycouril (TNGU), 1,4-dinitroglycouril (DNGU), 2-
oxo-1,3,5-trinitro-1,3,5-triazacyclohexane (K-6), which have attrac-
tive densities and performances.12–14 As too little research is avail-
able to synthesize aromatic nitroureas compounds, our interest
focuses on combing the benzene ring with cyclic nitrourea to form
fused ring compounds, which exhibit good thermochemical and
physical properties.15,16 In addition, these compounds may have
the insensitivity and stability associated with alternating amino
and nitro groups.
Nowadays, the design and synthesis of new energetic compounds
known as high-energy density materials (HEDMs) has been the
focus. In the pursuit of new HEDMs, considerable efforts have
been devoted to developing high-nitrogen heterocycles, and most
energy derives from a combination of positive heats of formation
and generation of large volumes of environmentally benign
nitrogen gas under decomposition.1–4 However, highly nitrated
cages or ring heterocycles and carbocycles are also interesting as
energetic materials because of the increased performance expected
from the additional energy release (manifested in a higher heat of
In our continuing effort to seek new energetic materials, here
we present our attempts at designing and synthesizing new
nitro derivatives using 5-amino-1H-benzo[d]imidazol-2(3H)-one
(1) as the primary material (Scheme 1).
Scheme 1
aSchool of Chemical Engineering, Nanjing University of Science & Technology, Nanjing
210094, China. E-mail: qz_yao@163.com; Fax: +86 25 8431 5030; Tel: +86 25 8431
8865
bSchool of Pharmacy, China Pharmaceutical University, Nanjing 210009, China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra04796f
Experimental
Caution
The titled compound is energetic material and tends explode
under certain conditions. Proper protective measures (safety
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glasses, face shields, leather coat, ear plugs and earthening MHz): d 10.49 (s, 1H), 10.40 (s, 1H), 9.15 (s, 1H), 7.23 (s, 1H), 6.93 (d,
equipment and person) should be taken during the synthesis, J ¼ 8.20 Hz, 1H), 6.77 (d, J ¼ 8.20 Hz, 1H), 1.46 (s, 9H); 13C NMR
test and measurement processes, especially when these (DMSO-d6, 125 MHz): d 155.00, 152.39, 132.59, 129.24, 124.24,
compounds are prepared on a larger scale.
110.42, 107.63, 99.21, 78.10, 27.66; anal. calcd for C12H15N3O3: C,
57.82; H, 6.07; N, 16.86; found: C, 57.70; H, 6.16; N, 16.80%; MS
(ESI) m/z: 250.02 (M + H).
Materials and instruments
2-Chloro-N-(2-oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)-
The starting materials used in the present study were of AR acetamide (4). To a stirred solution of 5-amino-1H-benzo[d]
grade and purchased from the trade without further purica- imidazol-2(3H)-one (1) (1.0 g, 6.7 mmol) in acetonitrile (30 mL),
tion. Melting point was measured on a X-4 melting point was added dropwise chloroacetyl chloride (1.5 mL) at room
apparatus and was uncorrected. 1H NMR (500 MHz) and 13C temperature, and maintained for 40 min. The reaction mixture
NMR (125 MHz) were recorded on Bruker Avance Spectrometer was then ltered, washed with water, and dried to give 2-chloro-
(TMS as an internal standard). Chemical shis (d) are reported N-(2-oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)acetamide (4) as
in part per million (ppm). The coupling constants (J) are a pale pink solid (1.36 g, 90%), m.p. >300 ꢁC; IR: 3289, 2997,
1
reported in hertz (Hz). High-resolution mass spectra were 1729, 1675, 1653, 1539, 1505, 1473, 1203, 1027, 845 cmꢀ1; H
recorded on a Finnigan TSQ Quantum ultra AM mass spec- NMR (DMSO-d6, 500 MHz): d 10.60 (s, 1H), 10.55 (s, 1H), 10.18
trometer. Elemental analysis was carried out on Perkin-Elmer (s, 1H), 7.45 (s, 1H), 7.02 (d, J ¼ 8.30 Hz, 1H), 6.86 (d, J ¼ 8.30 Hz,
instrument.
1H), 4.22 (s, 2H); 13C NMR (DMSO-d6, 125 MHz): d 163.57,
Theoretical calculations were carried out by using the 154.97, 131.54, 129.18, 125.55, 111.51, 107.81, 100.28, 43.10;
Gaussian 09 program suite.17 The geometry optimization of the anal. calcd for C9H8ClN3O2: C, 47.91; H, 3.57; N, 18.62; found: C,
molecular structure and frequency analyses were carried out by 47.85; H, 3.48; N, 18.68%; MS (ESI) m/z: 225.96 227.97 ¼ 3 : 1 (M
using the B3LYP functional with the 6-31G** basis set. The + H).
optimized structure was characterized to be true local energy
N-(1,3-Diacetyl-2-oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)-
minima on the potential-energy surface without imaginary acetamide (5). 5-Amino-1H-benzo[d]imidazol-2(3H)-one (1) (6.0 g,
frequencies. The designed isodesmic reactions for the predic- 40.3 mmol) was dissolved in 60 mL of acetic anhydride, the
tion of (DH0f gas) are discussed in the ESI.†18,19
reaction mixture was heated to 120 ꢁC and maintained three
5-Amino-1,3,6-trinitro-1H-benzo[d]imidazol-2(3H)-one (2). hours at this temperature, then the precipitate was cooled to 0 ꢁC,
(a) From 1: 5-amino-1H-benzo[d]imidazol-2(3H)-one (1) (3.0 g, ltered off, thoroughly washed with dichloromethane, then
20.1 mmol) was added slowly to a solution of fuming nitric acid water, and dried to give N-(1,3-diacetyl-2-oxo-2,3-dihydro-1H-
(6 mL) and acetic anhydride (50 mL) which was stirred at the ice benzo[d]imidazol-5-yl)acetamide (5) as a white solid (10.5 g,
ꢁ
bath. The reaction mixture was kept stirring for 30 min, and 95%), m.p. 248–250 C (dec.); IR: 1762, 1703, 1485, 1431, 1360,
poured into crushed ice, and then ltered, washed with water 1313, 1243, 1179, 1011, 823 cmꢀ1; 1H NMR (DMSO-d6, 500 MHz):
and dried to give 5-amino-1,3,6-trinitro-1H-benzo[d]imidazol- d 10.10 (s, 1H), 8.43 (s, 1H), 8.00 (d, J ¼ 8.85 Hz, 1H), 7.56 (d, J ¼
2(3H)-one (2) as a yellow solid (0.6 g, 11%); IR: 3073, 2246, 1732, 8.85 Hz, 1H), 2.64 (s, 3H), 2.63 (s, 3H), 2.03 (s, 3H); 13C NMR
1603, 1560, 1510, 1440, 1370, 1324, 1238, 1210, 1116, 983, 824 (DMSO-d6, 125 MHz): d 169.72, 169.46, 167.71, 150.39, 135.91,
cmꢀ1; 1H NMR (DMSO-d6, 500 MHz): d 12.59 (s, 2H), 8.55 (s, 1H), 126.18, 121.41, 114.67, 113.97, 105.47, 25.45, 25.27, 23.45; anal.
8.14 (s, 1H); 13C NMR (DMSO-d6, 125 MHz): d 154.59, 141.55, calcd for C13H13N3O4: C, 56.72; H, 4.76; N, 15.27; found: C, 56.65;
138.60, 132.65, 112.70, 107.45, 98.65; anal. calcd for C7H4N6O7: H, 4.71; N, 15.35%; MS (ESI) m/z: 297.95 (M + Na).
C, 29.59; H, 1.42; N, 29.58; found: C, 29.51; H, 1.35; N, 29.50%.
N-(2-Oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)acetamide (6).
(b) From 11: 1-acetyl-5-amino-6-nitro-1H-benzo[d]imidazol- 5-Amino-1H-benzo[d]imidazol-2(3H)-one (1) (5.0 g, 33.56 mmol)
2(3H)-one (11) (0.20 g, 0.8 mmol) was added very slowly to a was dissolved in 5ꢁ0 mL of acetic anhydride, the reaction mixture
solution of 20% N2O5/HNO3 (1 g) and
2 mL of tri- was heated to 40 C and maintained four hours at this temper-
uoromethanesulfonic acid (TFMSAA) which was stirred at the ature, then the precipitate was cooled to 0 ꢁC, ltered off, washed
ice bath. The reaction mixture was maintained stirring for 20 with dichloromethane, and then water, and dried to give N-(2-
min, and poured into crushed ice, then ltered, washed with oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)acetamide (6) as
water and dried to give 5-amino-1,3,6-trinitro-1H-benzo[d]imi- white solid (6.3 g, 98%), m.p. >300 ꢁC; IR: 2989, 1719, 1651, 1621,
dazol-2(3H)-one (2) as a yellow solid (0.18 g, 75%), whose 1H 1539, 1501, 1364, 1273, 1254, 1203, 1157, 1029, 885 cmꢀ1 1H
NMR was identied with an authentic sample. NMR (DMSO-d6, 500 MHz): d 10.51 (s, 1H), 10.45 (s, 1H), 9.77 (s,
a
;
tert-Butyl-2-oxo-2,3-dihydro-1H-benzo[d]imidazol-5-ylcarbamate 1H), 7.45 (s, 1H), 6.83 (d, J ¼ 7.9 Hz, 1H), 6.81 (d, J ¼ 7.9 Hz, 1H),
(3). To a stirred solution of 5-amino-1H-benzo[d]imidazol-2(3H)-one 2.00 (s, 3H); 13C NMR (DMSO-d6, 125 MHz): d 167.18, 154.98,
(1) (1.0 g, 6.7 mmol) in methanol (30 mL), dibutyldicarbonate (2.5 132.52, 129.08, 124.86, 111.06, 107.65, 100.05, 23.40; anal. calcd
mL) was added dropwise at room temperature. The reaction for C9H9N3O2: C, 56.54; H, 4.74; N, 21.98; found: C, 56.48; H, 4.67;
mixture was evaporated aer 30 min, and crystallized in methanol N, 22.05%; MS (ESI) m/z: 214.02 (M + Na).
to
give
tert-butyl-2-oxo-2,3-dihydro-1H-benzo-[d]imidazol-5-
2-Chloro-N-(4,6-dinitro-2-oxo-2,3-dihydro-1H-benzo[d]imidazol-
ylcarbamate (3) as a pale pink solid (1.9 g, 96%), m.p. 245–247 ꢁC 5-yl)acetamide (7). 2-Chloro-N-(2-oxo-2,3-dihydro-1H-benzo[d]
(dec.); IR: 3344, 3125, 2984, 1694, 1643, 1512, 1474, 1388, 1291, imidazol-5-yl)acetamide (4) (3.0 g, 13.3 mmol) was added slowly
1235, 1211, 1163, 1053, 1024, 852 cmꢀ1; H NMR (DMSO-d6, 500 to a solution of fuming nitric acid (4 mL) and concentrated sulfuric
1
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acid (50 mL) which was stirred at the ice bath. The reaction 10.19 (s, 1H), 7.54 (s, 1H), 7.50 (s, 1H), 2.10 (s, 3H); 13C NMR
mixture was kept stirring for 40 min, and poured into crushed ice, (DMSO-d6, 125 MHz): d 168.09, 155.12, 134.78, 133.81, 127.71,
and then ltered, washed with water and dried to give 2-chloro-N- 125.67, 104.11, 103.04, 23.44; anal. calcd for C9H8N4O4: C, 45.77;
(4,6-dinitro-2-oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)acetamide
H, 3.41; N, 23.72; found: C, 45.70; H, 3.35; N, 23.81%; MS (ESI) m/
(7) as a pale yellow solid (2.5 g, 60%); m.p. 300–302 ꢁC (dec.); IR: z: 234.92 (M ꢀ H).
3332, 3231, 2989, 1742, 1688, 1614, 1514, 1403, 1352, 1293, 1187,
993 cmꢀ1; 1H NMR (DMSO-d6, 500 MHz): d 12.03 (s, 1H), 11.83 (s,
Results and discussion
1H), 10.31 (s, 1H), 7.37 (s, 1H), 4.31 (s, 2H); 13C NMR (DMSO-d6,
125 MHz): d 165.78, 154.86, 133.73, 132.36, 124.95, 123.66, 122.76, An investigation of the new amino and nitro substituted 1H-
109.99, 42.14; anal. calcd for C9H6ClN5O6: C, 34.25; H, 1.92; N, benzo[d]imidazol-2(3H)-one as energetic material is now
22.19; found: C, 34.30; H, 1.85; N, 22.12%; MS (ESI) m/z: undertaken. With
a
view to synthesize N,C-nitro-
313.84 : 315.83 ¼ 3 : 1 (M ꢀ H).
benzimidazolones, we examined nitration reaction of
N-(1,3-Diacetyl-6-nitro-2-oxo-2,3-dihydro-1H-benzo[d]imidazol- compound 5-amino-1H-benzo[d]imidazol-2(3H)-one (1) wꢁith
5-yl)acetamide (8). N-(1,3-Diacetyl-2-oxo-2,3-dihydro-1H-benzo[d] fuming nitric acid/acetic anhydride at a temperature of 10 C,
imidazol-5-yl)acetamide (5) (3.0 g, 10.9 mmol) was added slowly and no compound was obtained, but an important product 5-
to a solution of fuming nitric acid (5 mL) and concentrated amino-1,3,6-trinitro-1H-benzo[d]imidazol-2(3H)-one (2) was
sulfuric acid (50 mL) which was stirred at the ice bath. The reac- synthesized at a lower temperature of the ice bath with a too low
tion mixture was kept stirring for 40 min, and poured into yield of 11%, which was possibly due to the unstable primary
crushed ice, and then ltered, washed with water and dried to give amino group in the benzene ring under strongly oxidizing
N-(1,3-diacetyl-6-nitro-2-oxo-2,3-dihydro-1H-benzo[d]imidazol- conditions (Scheme 1). Other nitrating reagents including metal
5-yl)acetamide (8) as a yellow solid (2.88 g, 83%), m.p. 208–210 ꢁC; nitrate like cupric nitrate, fuming nitric acid/concentrated
IR: 3356, 3304, 1733, 1712, 1671, 1608, 1494, 1367, 1317, 1278, sulfuric acid, concentrated sulfuric acid/potassium nitrate,
1
1165, 1100, 1067, 1003 cmꢀ1; H NMR (DMSO-d6, 500 MHz): d and even nitrogen pentoxide/fuming nitric acid were tried to
10.41 (s, 1H), 8.59 (s, 1H), 8.42 (s, 1H), 2.67 (s, 3H), 2.66 (s, 3H), react with compound 1, but all resulted in compound 2 in a low
2.08 (s, 3H); 13C NMR (DMSO-d6, 125 MHz): d 169.74, 169.54, yield. Thus, it was proposed to synthesize compound 2 or its
167.98, 150.04, 137.65, 129.97, 128.89, 122.44, 110.08, 25.30, derivatives through multistep strategy, including N-protection
25.07, 22.93; anal. calcd for C13H12N4O6: C, 48.75; H, 3.78; N, and succedent deprotection–nitration reaction.
17.49; found: C, 48.69; H, 3.70; N, 17.41%; MS (ESI) m/z: 342.94
(M + Na).
An efficient and economical technology for the anchoring of
1H-benzo[d]imidazol-2(3H)-one derivatives via the protection of
N-(4,6-Dinitro-2-oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)- the amino group was investigated. Dibutyldicarbonate (DIBOC),
acetamide (9). N-(2-Oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl) chloroacetyl chloride, and acetic anhydride were chosen to give
acetamide (6) (2.0 g, 10.5 mmol) was added slowly to a solu- corresponding N-substituted intermediates tert-butyl 2-oxo-2,3-
tion of fuming nitric acid (3 mL) and concentrated sulfuric acid dihydro-1H-benzo[d]imidazol-5-ylcarbamate (3), 2-chloro-N-(2-
(40 mL) which was stirred at the ice bath. The reaction mixture oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)acetamide (4), N-(1,3-
was kept stirring for 30 min, and poured into crushed ice, and diacetyl-2-oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)acetamide
then ltered, washed with water and dried to give N-(4,6-dinitro- (5),
and
N-(2-oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)-
2-oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)acetamide (9) as a acetamide (6), respectively. Compounds 4, 5 and 6 are poorly
ꢁ
yellow solid (2.45 g, 83%), m.p. >300 C; IR: 3346, 3242, 2989, soluble in organic solvents, as compared to compound 3, and
1738, 1678, 1604, 1547, 1510, 1476, 1410, 1296, 1246, 1176, 993 they could be brought into further nitration without additional
1
cmꢀ1; H NMR (DMSO-d6, 500 MHz): d 11.97 (s, 1H), 11.77 (s, purication.
1H), 9.96 (s, 1H), 7.33 (s, 1H), 2.03 (s, 3H); 13C NMR (DMSO-d6,
Subsequent nitration of compound 3 was the rst attempt,
125 MHz): d 169.02, 154.88, 133.50, 132.22, 124.54, 122.76, but in no case could any sign of the nitration product be
110.30, 22.39; anal. calcd for C9H7N5O6: C, 38.44; H, 2.51; N, detected, even at the ice bath. However, nitration of 4, 5 and 6
24.91; found: C, 38.38; H, 2.45; N, 24.99%; MS (ESI) m/z: 279.90 gave mono- or di-C-nitro derivatives, without N-nitro derivatives
(M ꢀ H).
or removal of N-protected groups. The nitration of 4 and 6 with
1-Acetyl-5-amino-6-nitro-1H-benzo[d]imidazol-2(3H)-one (11). excess nitric acid in concentrated sulfuric acid at the ice bath
N-(1,3-Diacetyl-6-nitro-2-oxo-2,3-dihydro-1H-benzo[d]imidazol-5- gave C-dinitro derivatives 2-chloro-N-(4,6-dinitro-2-oxo-2,3-
yl)acetamide (8) (0.5 g, 1.56 mmol) was dissolved in 20 mL of dihydro-1H-benzo[d]imidazol-5-yl)acetamide (7) and N-(4,6-
acetonitrile, and then 0.5 mL of 1,8-diazabicyclo[5.4.0]undec-7- dinitro-2-oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)acetamide
ene was added dropwise, the reaction mixture gradually turned (9), respectively (Scheme 2). And nitration of 5 gave mono-C-
into red. Aer 30 min, the reaction mixture was evaporated, and nitro derivative N-(1,3-diacetyl-6-nitro-2-oxo-2,3-dihydro-1H-
added 10 mL of water, the yellow solid was precipitated aer benzo[d]imidazol-5-yl)acetamide (8) (Scheme 3). Owing to the
standing for 25 min. the mixture was ltered, washed with water, decrease of aromatic ring electron density, caused by three
and dried to give 1-acetyl-5-amino-6-nitro-1H-benzo[d]imidazol- acetyl groups attached to the benzene ring of compound 5
ꢁ
2(3H)-one (11) (0.3 g, 81%); m.p. >300 C; IR: 3463, 3332, 3066, indirectly, di-C-nitro reactions are unlikely to happen. Further
1719, 1698, 1646, 1614, 1557, 1488, 1369, 1316, 1274, 1173, 1065, nitration of 4, 5 and 6 with a variety of nitrating agents, such as
1
1018, 917 cmꢀ1; H NMR (DMSO-d6, 500 MHz): d 11.15 (s, 2H), concentrated sulfuric acid/fuming nitric acid, fuming nitric
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Scheme 2
Fig. 1 The DSC curve of compound 2.
Scheme 3
of the nal acetyl group to give 5-amino-1,3,6-trinitro-1H-benzo
[d]-imidazol-2(3H)-one (2). Thus, using 1 as a starting material,
2 was obtained by N-protected reaction, nitration, deprotection
and again nitration reaction with an overall-yield of 48%.
In order to investigate the thermal behavior of compound 2,
ꢀ1
ꢁ
the DSC curve (with a linear heating rate of 10 C min in N2
gas owing at a rate of 20 mL minꢀ1) is shown in Fig. 1. The DSC
curve of compound 2 exhibits clearly an exothermic decompo-
sition reaction with peak maximum at 185.34 ꢁC and energy
evolved during the decomposition reaction is 888 J gꢀ1. Thus,
compound 2 has a lower thermal stability comparing with 1,3,5-
triamino-2,4,6-trinitrobenzene (TATB), whose melting point is
Scheme 4
350 C.20
Detonation velocity (D) and detonation pressure (P) are the
ꢁ
acid/acetic anhydride, fuming nitric acid/fuming sulfuric acid,
triuoroacetic anhydride/fuming nitric acid showed the same
results. So it is likely that the synthesis of compound 2 involved
a multi-step reaction sequence in which compound 1 was N-
protected, nitrated, deprotected and renitrated.
most important targets of scaling the detonation characteristics
of energetic materials. For the explosives with CHNO elements,
the Kamlet–Jacobs empirical equations21,22 was used to deter-
mine these parameters.
The C-dinitro derivatives 7 and 9 were difficult to generate
the deprotected derivative 10 by treatment with concentrated
hydrochloric acid or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)
in acetonitrile (Scheme 4). To our delight, the triacetyl
compound 8 is easy to convert into mono-acetyl derivative 1-
acetyl-5-amino-6-nitro-1H-benzo[d]imidazol-2(3H)-one (11) in
the presence of DBU (Scheme 5). The nitrolysis of the nal acetyl
group of compound 11 proved to be very difficult. Several
nitrolysis reagents were tried including fuming nitric acid/
acetic anhydride, fuming nitric acid/concentrated sulfuric
acid, concentrated sulfuric acid/potassium nitrate, nitrogen
pentoxide/fuming nitric acid, but all resulted in recovery of the
starting material. The development of the powerful nitration
reagent, triuoromethanesulfonic acid anhydride (TFMSAA)/
nitrogen pentoxide/fuming nitric acid, allowed the nitrolysis
Kamlet–Jacobs empirical equations:
D ¼ 1.01(NM0.5
Q
)
0.5 0.5(1 + 1.30ro)
(1)
(2)
P ¼ 1.55ro2NM0.5Q0.5
where D is detonation velocity in km sꢀ1, P is detonation pres-
sure in GPa, N is moles of gaseous detonation products per
gram of explosives, M is the average molecular weights of
gaseous products, Q is the energy of explosion in J gꢀ1 of
explosive and ro is the crystal density in g cmꢀ3. N, M and Q are
determined according to the largest exothermic principle, i.e.,
for the explosives with CHNO elements, all the N atom converts
into N2, the O atom forms H2O with H atom rst and the
remainder forms CO2 with C atom. The remainder of C atom
will exist in solid state if O atom does not satisfy full oxidation of
C atom. The remainder of O atom will exist in O2 if O atom is
superuous.
Density (r), Oxygen balance (OB), detonation velocity (D) and
detonation pressure (P) are of the most important four factors in
determining the performance of energetic compounds. The
density of compound 2 was 1.83 g cmꢀ3, which was mainly
attributed to the inherently high density of the urea framework.
Scheme 5
42218 | RSC Adv., 2014, 4, 42215–42219
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RSC Advances
Oxygen balance is a measure of how much oxygen is required 11 P. F. Pagoria, G. S. Lee, A. R. Mitchell and R. D. Schmidt,
for complete combustion of hydrogen to water and carbon to Thermochim. Acta, 2002, 384, 187.
carbon dioxide. A positive or negative oxygen balance signies 12 Z. J. Peng and D. Z. Wan, Acta Armamentarii, 1980, 3, 23.
that there is an excess of or a deciency of oxygen in the 13 C. Zhou, Y. S. Zhou, B. Z. Wang, H. Huo, F. Q. Bi, P. Lian and
molecule for complete combustion. And compound 2 (D ¼ 7.78
X. Z. Fan, Chin. J. Org. Chem., 2012, 32, 75.
km sꢀ1, P ¼ 27.05 GPa, OB ¼ ꢀ50.70%) exhibits better deto- 14 C. M. Ma, Z. L. Liu and Q. Z. Yao, Chin. J. Energ. Mater., 2014,
nation performance than 2,4,6-trinitrotoluene (TNT, D ¼ 7.21
22, 263.
km sꢀ1, P ¼ 22.49 GPa, OB ¼ ꢀ74% (ref. 23)).
15 V. Thottempudi, F. Farhad, D. A. Parrish and J. M. Shreeve,
Angew. Chem., Int. Ed., 2012, 51, 9881.
16 R. D. Chapman, W. S. Wilson, J. W. Fronabarger,
L. H. Merwin and G. S. Ostrom, Thermochim. Acta, 2002,
384, 229.
Conclusions
The present investigation demonstrates the synthesis of some
new nitro derivatives for 5-amino-1H-benzo[d]imidazol-2(3H)-
one namely, 5-amino-1,3,6-trinitro-1H-benzo[d]imidazol-2(3H)-
one (2), 2-chloro-N-(4,6-dinitro-2-oxo-2,3-dihydro-1H-benzo[d]
imidazol-5-yl)acetamide (7), N-(1,3-diacetyl-6-nitro-2-oxo-2,3-
dihydro-1H-benzo[d]imidazol-5-yl)acetamide (8), N-(4,6-dinitro-
2-oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)acetamide (9), 1-
acetyl-5-amino-6-nitro-1H-benzo[d]imidazol-2(3H)-one (11). The
newly synthesized compounds have been characterized by
elemental and spectral analysis data. The compound 2 has been
evaluated for thermal and some detonation performances.
17 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, T. Vreven, J. A. J. Montgomery,
J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd,
E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi,
J. Normand, K. Raghavachari, A. Rendell, J. C. Burant,
S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam,
M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev,
A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski,
R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth,
P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,
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