at 20–22 ꢀC over half an hour. After complete addition of
sodium azide, the stirring was continued for another 3 h
while maintaining the same temperature. The reaction mixture
was poured into crushed ice and left overnight to precipitate.
The product, which settled out, was filtered off, washed
thoroughly with distilled water and finally dried at room
H, 1.22; N, 24.07; found : C, 35.16; H, 1.10; N, 23.85%.
7-(2,4,6-Trinitro-1-iminophenyl)-4,6-dinitrobenzofuroxan, 5.
In a three-necked round-bottom flask fitted with reflux
condenser and dropping funnel, 2 (5.21 g, 20 mmol) was
introduced with 2,4,6-trinitroaniline (9.20 g, 40.35 mmol) to
which 150 ml of methanol was added. The reaction mixture
was refluxed for 5 h, cooled down to ambient temperature
and finally poured into crushed ice. The yellow precipitate
thus obtained was filtered off, washed with water and dried
in a water-jacketed oven at 60 ꢀC. The product was further
recrystallised from dichloromethane to yield 7.5 g (83%) of
pure product; mp 179–80 ꢀC. The DTA results showed no
exotherm up to 400 ꢀC. IR (KBr) cm 1: 3322 (m, N H str),
3082 (m, Ar H str), 1636, 1590, 1495, 1274 (mw, furoxan
ring), 1528 and 1274 (s, NO2 asym and sym str), 934 (m,
temperature. Yield 4.2
g (92%). The compound was
recrystallised from methanol and was found to melt at 45–
47 ꢀC. IR (KBr) cm 1: 3089 (m, Ar H str), 2165 (s, N3)
1616 (m, C¼C str), 1545 and 1335 (s, NO2 asym and sym
str). 1H-NMR (DMSO-d6 , TMS) d: 8.5 (s, 1H, aromatic
proton). Anal. calc. for C6HN6O6Cl (MW 288): C, 25.00; H,
0.34; N, 29.17; found: C, 24.89; H, 0.46; N, 29.01%.
7-Chloro-4,6-dinitrobenzofuroxan, 2. 1 (5 g, 17.33 mmol)
was carefully transferred into a two-necked flask fitted with a
reflux condenser and acetic acid (20 ml) was added. The
reaction mixture was refluxed for 2 h over an oil bath; the
mixture was then cooled to ambient temperature and
subsequently poured into crushed ice. The yellow precipitate
thus obtained was filtered off and washed with distilled water
until it was acid-free. The product was crystallised from
methanol. Yield 3.5 g (77%); mp 110–112 ꢀC; DTA: 114 ꢀC
(endotherm) and 205 ꢀC (exotherm). IR (KBr) cm 1: 3096
(m, Ar H str), 1620 and 1580 (m, C¼C and C¼N str), 1535
1
substituted benzene ring). H-NMR (CDCl3, TMS) d: 9.4 (s,
1H, benzofuroxan ring), 9.0 (s, 2H, trinitrophenyl ring), 7.30
(br, 1H, NH). EI-MS (70 eV) m=z: 264, 228 (100%), 212,
198, 166, 152, 137, 107, 91. Anal. calc. for C12H4N8O12
(MW 452): C, 31.85; H, 0.88; N, 24.77; found: C, 31.75; H,
1.06; N 24.56%.
Results and discussion
1
and 1345 (s, NO2 asym and sym str), 815 (s, C Cl str). H-
NMR (DMSO-d6, TMS) d: 8.75 (s, 1H, aromatic proton).
Anal. calc. for C6HN4O6Cl (MW 260): C, 27.69; H, 0.38; N,
21.53; found C, 27.51; H, 0.26; N, 21.30%.
Synthesis and structure
7-Chloro-4,6-dinitrobenzofuroxan, 2, was synthesised from
styphnic acid following an essentially different route from that
of Norris et al.16 The reaction steps followed for the pre-
paration of the parent compound 2, along with compounds 3,
4 and 5 are outlined in Scheme 1. The dipyridinium styphnate
was prepared from styphnic acid by treatment with pyridine; it
was then chlorinated using phosphorus oxychloride. Azidation
of the chlorinated product and subsequent cyclisation pro-
duced 2, which was subsequently condensed with the nitro-
aniline derivatives, thus resulting in the target molecules with
very good yields and excellent purity. This method of pre-
paration of the nitroanilinobenzofuroxans has been achieved
even more conveniently through a simplified method for the
preparation of the halide benzofuroxans, 2, which can be used
without further purification. Mention is made here of the
possibilities for large-scale synthesis of thermally stable,
insensitive energetic molecules and their parent compounds
from inexpensive starting materials.
Compounds 3, 4 and 5 are light yellow to dark yellow solids
and the analytical and spectroscopic data unambiguously
proved the structures of the compounds with no evidence of
isomeric structures. This is further supported by the fact that
formation of the furazan oxide involves ring opening to give an
‘‘ortho-dinitrosobenzene’’ as a transient intermediate, fol-
lowed by very rapid interconversion to the cyclised product.17
The X-ray crystallography18 and electrospectroscopy for che-
mical analysis (ESCA)19 results, together with IR, 1H-NMR
and mass spectrometry, further confirmed the structures of the
benzofuroxans.
The EI-MS fragmentation species suggested below are ten-
tative in the absence of the use of techniques such as accurate
mass measurement, fast atom bombardment and chemical
ionisation, as well as the mass spectra of deuterated analogues.
The EI-MS of these compounds were expected to show similar
patterns; however, on analysing the results we found that the
number of nitro groups and their positions in the aromatic ring
greatly influence the decomposition pathways and species.
The mass spectral data (relative intensity >5%) of com-
pounds 3, 4 and 5 are given in the experimental section. The EI
mass spectra show no molecular ions, nevertheless, certain
interesting ions that are of diagnostic value offer a means to
7-(4-Nitrophenylamino)-4,6-dinitrobenzofuroxan, 3. To a 250
ml three-necked round-bottom flask fitted with mechanical
stirrer, dropping funnel and reflux condenser, 2 (5.21 g, 20
mmol) was transferred and 4-nitroaniline (5.6 g, 40.57 mmol)
was added along with 125 ml of methanol. The reaction
mixture was refluxed for 5 h and subsequently cooled down
to ambient temperature. The reaction mixture was placed
into ice-cold water. The off-yellow precipitate thus obtained
was filtered off on a Buchner funnel and washed with water.
The product was crystallised from dichloromethane. Yield 5.6
g (77.3%); the compound did not melt but decomposed at
172 ꢀC (DTA exotherm). IR (KBr) cm 1: 3266 (m, N H str),
3116 (m, Ar H str), 1636, 1594, 1495, 1250 (mw, furoxan
ring), 1526 and 1346 (s, NO2 asym and sym), 940 (m,
1
substituted benzene ring). H-NMR (chloroform-d1, TMS) d:
8.9 (s, 1H, aromatic proton), 8.1 (s, 2H, aromatic proton), 7.7
(s, 2H, aromatic proton), 6.8 (br s, 1H, NH). EI-MS (70 eV)
m=z: 279, 264, 235, 189, 164, 138 (100%), 152, 107, 91. Anal.
calc. for C12H6N6O8 (MW 362): C, 39.77; H 1.65; N, 23.20;
found: C, 39.54; H, 1.83; N, 22.96%.
7-(3,5-Dinitrophenylamino)-4,6-dinitrobenzofuroxan, 4. 2 (25.21
g, 20 mmol) and 3,5-dinitroaniline (7.4 g, 40.43 mmol) were
carefully transferred into a 250 ml three-necked round-bottom
flask fitted with mechanical stirrer and reflux condenser,
followed by 130 ml of methanol. The reaction mixture was
refluxed for 5 h, then cooled down to ambient temperature and
poured into crushed ice. The yellow precipitate thus obtained
was filtered off and washed with distilled water and was
crystallised from dichloromethane. Yield 6.5 g (79.8%); the
product did not melt, however, the DTA was recorded and the
endotherm found at 95 ꢀC and the exotherm at 260 ꢀC. IR
1
(KBr) cm
1588, 1490,1294 (mw, furoxan ring), 1538 and 1342 (s, NO2
: 3378 (m, N H str), 3088 (m, Ar H str), 1640,
1
asym and sym str), 956 (m, substituted benzene ring). H-NMR
(CDCl3, TMS) d: 9.1 (s, 1H, benzofuroxan ring), 8.37 (s, 1H,
phenyl), 7.75 (s, 2H, phenyl ring), 7.15 (br s, 1H, NH). EI-MS
(70 eV) m=z: 285, 283, 264, 247, 183 (100%), 169, 154, 137,
1550
New J. Chem., 2001, 25, 1549–1552