Synthesis of benzotriazolo[1,2-a]benzotriazole derivatives as new high density, insensitive energetic materials

Article abstract of DOI:10.1021/jo9608836

The synthesis of the new high density energetic compound 4,8-dinitro-12H-[1,2,5]-oxadiazolo[3,4-e][1,2,5]oxadiazolo[3′,4′:4, 5]benzotriazolo[1,2-a]benzotriazol-13-ium inner salt 1,11-dioxide (7) was achieved in three steps (37% yield) from 2,4,8,10-tetranitrobenzotriazolo[1,2-a]benzotriazolo-6-ium inner salt (4). The compound 7 was found to be thermally stable up to 274 °C and was insensitive to impact (hammer/anvil test).

Full text of DOI:10.1021/jo9608836

J . Org. Chem. 1996, 61, 5801-5803
5801
Syn th esis of Ben zotr ia zolo[1,2-a ]ben zotr ia zole Der iva tives a s New
High Den sity, In sen sitive En er getic Ma ter ia ls
Ganesan Subramanian, Genevieve Eck, J oseph H. Boyer, Edwin D. Stevens, and
Mark L. Trudell*
Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148
Received May 14, 1996X
The synthesis of the new high density energetic compound 4,8-dinitro-12H-[1,2,5]-oxadiazolo[3,4-
e][1,2,5]oxadiazolo[3′,4′:4,5]benzotriazolo[1,2-a]benzotriazol-13-ium inner salt 1,11-dioxide (7) was
achieved in three steps (37% yield) from 2,4,8,10-tetranitrobenzotriazolo[1,2-a]benzotriazolo-6-ium
inner salt (4). The compound 7 was found to be thermally stable up to 274 °C and was insensitive
to impact (hammer/anvil test).
In tr od u ction
The compounds triaminotrinitrobenzene (1, TATB),1
2,6-dipicrylbenzo[1,2-d][4,5-d′]bis-triazole-4,8-dione (2),2
2,4,8,10-tetranitrobenzotriazolo[2,1-a ]benzotriazol-6-
ium inner salt (3, z-Tacot),3,4 2,4,8,10-tetranitrobenzo-
triazolo[1,2-a]benzotriazol-6-ium inner salt (4, y-Tacot),5,6
and more recently 5-nitro-4,6-bis(5-amino-3-nitro-1H-
1,2,4-triazol-1-yl)pyrimidine (5, DANTNP)7 have been
developed as insensitive energetic materials for a variety
of industrial and military applications (Figure 1). How-
ever, despite favorable insensitivity to heat, impact, and
electric shock, the density and energetic properties
(detonation velocity, D; detonation pressure, PCJ ) of these
compounds are inferior to those observed for the explo-
sives RDX and HMX.8,9
The design and synthesis of new insensitive energetic
compounds with high density and improved energetic
properties has been the focus of recent studies in our
laboratories.11-13 Because of the inherent thermal stabil-
ity of the dibenzotetraazapentalene ring system, 3 and
4 were identified as attractive precursors for the develop-
ment of new classes of high density insensitive energetic
materials. Based on computed densities and energetic
properties, the nitro- and furoxano-substituted deriva-
tives 6 and 7 were envisaged as attractive synthetic
targets for development of new high density insensitive
X Abstract published in Advance ACS Abstracts, August 1, 1996.
(1) Urbanski, T.; Vasudeva, S. K. J . Sci. Ind. Res. 1978, 37, 250.
(2) Berlin, J . K.; Coburn, M. D. J . Heterocycl. Chem. 1975, 12, 235.
(3) Carboni, R. A.; Kauer, J . C.; Hatchard, W. R.; Harder, R. J . J .
Am. Chem. Soc. 1967, 89, 2626.
(4) Carboni, R. A. U.S. Patent 2,904,545, 1959.
(5) Kauer, J . C.; Carboni, R. A. J . Am. Chem. Soc. 1967, 89, 2633.
(6) Kauer, J . C. U.S. Patent 3,262,943, 1966.
(7) Wartenberg, C.; Charrue, P.; Lavel, F. Prop. Expl. Pyro. 1995,
20, 23.
(8) Nielsen, A. T. in Chemistry of Energetic Materials; Olah, G.;
Squire, D. R., Eds., Academic Press Inc.: New York, 1991; pp 95-
124.
F igu r e 1. Physical and energetic properties of several insen-
sitive energetic compounds. For those compounds in which the
energetic properties have not been experimentally determined
computed values (*) are indicated (see ref 10).
(9) Meyer, R. in Explosives, 3rd ed.; VCH: Weinheim, 1987, pp 150
and 201. [RDX (hexogen); mp 204 °C; d ) 1.81 g/cm3; D ) 8.85 mm/s]
[HMX (octogen); mp 282 °C; d ) 1.9 g/cm3; D ) 9.1 mm/s].
energetic compounds. The synthesis of 4,11-dinitro[1,2,5]-
oxadiazolo[3,4-e][1,2,5]oxadiazolo[3′,4′:4,5]benzotriazolo-
[2,1-a]benzotriazol-6-ium inner salt 1,8-dioxide (6, z-
DBBD) from 3 has recently been achieved in three steps
in 21% overall yield.11 The z-isomer 6 was found to be
thermally stable up to 310 °C and exhibited moderate
impact sensitivity (dropweight test (2.5 kg): 6, 19 cm;
RDXstd, 18 cm).13 The synthesis of the corresponding
y-isomer, 4,8-dinitro-12H-[1,2,5]oxadiazolo[3,4-e][1,2,5]-
oxadiazolo[3′,4′:4,5]benzotriazolo[1,2-a]benzotriazol-13-
ium inner salt 1,11-dioxide (7, y-DBBD) has recently been
(10) The density
d D (mm/s), and
(g/cm3), detonation velocity
detonation pressure PCJ (kbar) were computed with a program obtained
from the Naval Weapons Center, China Lake, CA.
(11) Subramanian, G.; Boyer, J . H.; Buzatu, D.; Stevens, E. D.;
Trudell, M. L. J . Org. Chem. 1995, 60, 6110.
(12) Subramanian, G.; Boyer, J . H.; Koppes, W.; Sitzmann, M. E.;
Nock, L. A.; Gilardi, R.; Russell, T. P.; Trudell, M. L. J . Org. Chem.
1996, 61, 1898.
(13) Trudell, M. L.; Subramanian, G.; Eck, G.; Boyer, J . H. In
Decomposition, Combustion and Detonation Chemistry of Energetic
Materials; Brill, T. B., Russell, T. P., Tao, W. C., Wardle, R. B., Eds.,
Materials Research Society Symposium Proceedings: Pittsburgh, PA,
1996; Vol. 418, pp 37-42.
S0022-3263(96)00883-3 CCC: $12.00 © 1996 American Chemical Society

5802 J . Org. Chem., Vol. 61, No. 17, 1996
Subramanian et al.
Sch em e 1
completed. Herein we wish to describe the synthetic
sequence and preliminary insensitivity data for 7.
F igu r e 2.
nitrogen bond of the trivalent nitrogen atoms.16 In the
X-ray structure of 4‚acetone, the electronegative oxygen
atoms of the carbonyl of acetone are uniformly oriented
throughout the crystal lattice toward this electropositive
region of the tetraazapentalene unit of 4. This is
consistent with the computational results and clearly
demonstrates for the first time the electronic nature of
intermolecular dipolar interactions in a tetraazapental-
ene system. The stoichiometric cocrystallization of sol-
vent molecules (acetone, DMF) has also been observed
(NMR, C,H,N) to take place with other tetraazapentalene
derivatives.11,12
With multigram quantities of 4 in hand, attention
turned toward further functionalization of the benzo
rings of 4 for the construction of the furoxan ring systems
of the initial target compound 7. Treatment of 4 with
sodium azide in dimethyl sulfoxide furnished a single
symmetrical diazido dinitro derivative in 83% yield
resulting from nucleophilic substitution of an equivalent
pair of nitro groups by the azide anion. The structure of
the compound is believed to be that of the symmetrical
isomer, 4,8-diazido-2,10-dinitro derivative 9 (Scheme 1).
From previous studies with z-Tacot (3), nucleophilic
substitution of the 4,10-nitro groups (adjacent to the
divalent nitrogen atoms of tetraazapentalene moiety) was
found to take place regiospecifically.11 By analogy, the
4,8-nitro groups of 4 are believed to be the site of azide
substitution resulting in the formation of 9.
Nitration of the diazido dinitro derivative 9 proceeded
easily to give the 4,8-diazido-2,3,9,10-tetranitro deriva-
tive 10 in 76% yield (Scheme 1). The ease of the nitration
of 9 stems from activation of the C(3)- and C(9)-positions
toward electrophilic attack by the ortho-directing effect
of the azido groups.17 Despite favorable computed den-
sity and improved computed energetic properties for 10
(d ) 1.84 g/cm3, D ) 8.12 mm/µs, PCJ ) 301 kbar),10 the
material was considerably more sensitive than 4. The
diazido tetranitro derivative 10 was found to have good
thermal stability (decomposed at 280 °C) but was impact
sensitive (violent explosion with flame when struck by a
hammer) while 4 was completely stable under these
conditions.
Resu lts a n d Discu ssion
Based on previous studies in the z-isomer system,11 the
synthesis of the target compound 7 was envisaged to
proceed from y-Tacot (4). The benzotriazolo[1,2-a]ben-
zotriazol-6-ium inner salt (8) was prepared from o-
phenylenediamine and 2-chloronitrobenzene according to
the procedure developed by Kauer and Carboni.4 Nitra-
tion of 8 was found to proceed cleanly with 90% HNO3/
H2SO4 at 0-5 °C, followed by a brief heating period (10
min) at 60-75 °C. This gave the 2,4,8,10-tetranitro
derivative 4 as the sole product in 86% yield (Scheme 1).
This modified procedure provided 4 in greater yield and
in a higher state of purity than the literature nitration
conditions.4 The tetranitro derivative 4 was found to be
a strongly fluorescent material [λf (acetone) 475 nm, Φ
(0.50)]. Although aromatic nitro compounds do not
usually possess good luminescent properties, the photo-
physical properties of 4 are characteristic of nitrated
benzotetraazapentalene derivatives.14 The orientation of
the nitro groups in 4 was unequivocally confirmed by
X-ray crystallography (Figure 2).15
From the X-ray structure, it is readily apparent that
one molecule of acetone cocrystallized per molecule of 4.
It is interesting to note that earlier computational studies
on simple tetraazapentalenes predicted that a positive
electrostatic potential existed above the nitrogen-
(14) Lu, Q.; Boyer, J . H. Heteroatom Chem. 1993, 4, 91.
(15) The authors have deposited atomic coordinates for 4‚acetone
with the Cambridge Crystallographic Data Center. The coordinates
can be obtained, on request, from the Director, Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, U.K.
(16) Politzer, P.; Seminario, J . M. Struct. Chem. 1990, 1, 325.
(17) Biffen, M. E. C.; Miller, J .; Paul, D. B. in The Chemistry of the
Azido Group; Patai, S., Ed., Wiley and Sons: New York, 1971.

Synthesis of Benzotriazolo[1,2-a]benzotriazole Derivatives
J . Org. Chem., Vol. 61, No. 17, 1996 5803
were outside the standard acceptable limit of (0.4%. How-
ever, duplicate and triplicate analyses for nitrogen were
usually within (3% of calculated values and corresponded to
the empirical formula of the compound. Ca u tion ! Com -
p ou n d s 4, 7, 9, a n d 10 sh ou ld be h a n d led a s p oten tia lly
exp losive m a ter ia ls!
Thermolysis of 10 furnished the new heterocyclic
system 4,8-dinitro-12H-[1,2,5]oxadiazolo[3,4-e][1,2,5]-
oxadiazolo[3′,4′:4,5]benzotriazolo[1,2-a]benzotriazol-13-
ium inner salt 1,11-dioxide (7) in 58% yield (Scheme 1).
This served to confirm the presence of two sets of
contiguous azido and nitro groups and supported the
structural assignment of 9. The structural asignment
of 7 was made based on the X-ray structure of z-isomer
6 in which the orientation of the exocyclic oxygen atoms
of the furoxan moieties occupied the least sterically
hindered site. In addition, the structure of 7 is consistent
with the structure of thermodynamically favored 4-ni-
trobenzofuroxans.18 However, it should also be noted
that without unequivocal confirmation of this structure
by X-ray crystallography, the isomer 7′ resulting from
the thermal isomerization of 7 must also be considered
as a possible structure.18
y-Ta cot (4). The dibenzotetraazapentalene 85 (15.6 g, 0.075
mol) was dissolved in sulfuric acid (195 mL), and the mixture
was cooled to 10 °C in an ice-bath. Nitric acid (90%, 300 mL)
was then added dropwise, keeping the flask temperature below
25 °C. After the addition was complete, the reaction mixture
was stirred for 15 min at room temperature and then heated
at 60-75 °C for 10 min. The mixture was cooled to 20 °C and
poured into ice-water (25 L). The yellow precipitate was
filtered, washed with water (3 × 100 mL), and dried. The
crude compound (25.8 g) was recrystallized from DMF (550
mL) to give 4 (25.1 g, 86%). An analytical sample was
prepared by recrystallization from acetone: mp 398 °C dec [lit.5
mp 400 °C (dec)]; IR (KBr) ν 3097, 1629, 1586, 1536, 1413,
1
1377, 726 cm-1; H NMR (DMSO-d6) δ 10.60 (d, J ) 1.9 Hz,
2H), 9.31 (d, J ) 1.8 Hz, 2H); 13C NMR (DMSO-d6) δ 142.8,
141.2, 135.0, 125.6, 120.7, 116.2; UV (acetone) λmax 452 nm,
log ꢀ 5.47; λf (acetone) 475 nm, Φ 0.50. Anal. Calcd for
C
12H4N8O8: C, 37.12; H, 1.04; N, 28.86. Found: C, 37.02; H,
1.02; N, 27.82.
4,8-Dia zid o-2,10-d in itr oben zotr ia zolo[1,2-a ]ben zotr ia -
zol-6-iu m In n er Sa lt (9). y-Tacot (4) (17.5 g, 45 mmol) and
sodium azide (23.4 g, 360 mmol) in dry DMSO (600 mL) were
heated at 70-75 °C for 24 h. The mixture was then cooled at
15 °C for 1.5 h, and the yellow-orange solid which separated
was collected by filtration and washed with ethyl alcohol (100
mL) and diethyl ether (100 mL) to give 9 (14.3 g, 83%). The
crude compound was used directly in the next step without
any further purification. A pure sample was prepared for
analysis by recrystallization from DMF: mp 175-176 °C dec;
The red microcrystalline material 7 was found to be
stable up to temperatures of 274 °C at which point the
material decomposed nonexplosively into a tarlike mate-
rial. In addition, 7 was found to be insensitive to impact
(hammer/anvil test). Although no detonation was ob-
served when the material was struck by a hammer, this
is a crude test and may not accurately reflect the
sensitivity of the compound. We have found a number
of moderately sensitive materials to be nonresponsive in
this test (i.e. 6, RDX).11 More accurate experimental
measurements have been required to define the sensitiv-
ity of these compounds.
1
IR (KBr) ν 3072, 2123, 1542, 1522, 1337, 1115, 741 cm-1; H
NMR (DMSO-d6) δ 9.82 (d, J ) 1.8 Hz, 2H), 8.20 (d, J ) 1.7
Hz, 2H), 2.80 (s, 3H, DMF), 2.72 (s, 3H, DMF). Anal. Calcd
for C12H4N12O4‚C3H7NO: C, 39.76; H, 2.43; N, 40.16. Found:
C, 39.71; H, 2.52; N, 39.27.
4,8-Dia zid o-2,3,9,10-tetr a n itr oben zotr ia zolo[1,2-a ]ben -
zotr ia zol-6-iu m In n er Sa lt (10). Nitric acid (90%, 47.5 mL)
was cooled in an ice-bath, and 9 (12.6 g, 0.033 mol) was added
keeping the temperature below 10 °C. Stirring was continued
for 2 h at 0-5 °C. The mixture was poured into ice-water (1
L), and the orange-brown precipitate was filtered, washed with
water (100 mL), and dried to give 10 (11.9 g, 76%). The crude
compound was dissolved in acetone (12.5 mL) at 40 °C. The
insoluble material was removed and triturated with hexane
(20 mL). The mixture was kept in a freezer overnight, and
the precipitate was filtered. The material was then recrystal-
lized from acetone to give 10 (0.9 g, 41%): mp 280 °C dec; IR
(KBr) ν 2144, 1558, 1507, 1339, 1320, 1292, 907, 820 cm-1; 1H
NMR (acetone-d6) δ 10.13 (s, 2H); 13C NMR (acetone-d6) δ
140.9, 136.8, 133.2, 124.2, 122.1, 108.7. Anal. Calcd for
Attempts to introduce additional nitro groups at the
C(1)- and C(13)-positions of 7 were unsuccessful. Similar
to the results obtained in the z-isomer system,12 at-
tempted nitration of 7 using highly reactive nitration
media (100% HNO3, FSO3H) resulted in the formation
of an intractable mixture of carbonyl-containing com-
pounds. As observed in the z-isomer system, the tet-
ranitro derivatives were very sensitive to moisture and
air such that the o-dinitro functionality readily decom-
posed to quinone-like species via an unusual hydrolysis/
oxidation reaction.12 In light of the chemical sensitivity
of these compounds further attempts to nitrate 7 have
been abandoned. The development of new heterocyclic
systems which exploit the insensitivity and thermal
stability of the tetraazapentalene ring system is currently
under investigation.
C
12H2N14O8‚C3H6O: C, 34.10; H, 1.53; N, 37.12. Found: C,
33.78; H, 1.58; N, 34.43.
y-BDDB (7). The tetranitrodiazide 10 (10.0 g, 21 mmol)
in 1,2-dichlorobenzene (650 mL) was heated for 1 h at 150 °C.
The mixture was cooled in an ice-bath for 2 h, and the
precipitate was filtered and washed with diethyl ether. The
filtrate was triturated with acetonitrile to give 7 (6.0 g, 58%)
in pure form: mp 274-275 °C dec; IR (KBr) ν 1654, 1575, 1534,
1414, 1330, 1296, 999, 704 cm-1; 1H NMR (DMSO-d6) δ 10.42
(s, 2H); 13C NMR (DMSO-d6) δ 146.6, 134.6, 132.5, 123.7, 117.2,
107.5. Anal. Calcd for C12H2N10O8: C, 34.80; H, 0.49; N,
33.82. Found: C, 34.78; H, 0.58; N, 31.23.
Exp er im en ta l Section
All chemicals were purchased from Aldrich Chemical Co.,
Milwaukee, WI. Reported UV absorptions are restricted to
the longest wavelength. Fluorescence quantum yields were
determined for solutions in EtOH or DMF with excitation at
460, 540, and 570 nm with sulfarhodamine (Φ ) 0.68) and
acridine orange (Φ ) 0.46) as references. Melting points and
decomposition points are uncorrected. Elemental analyses
were obtained from Galbraith Laboratories, Inc., Knoxville,
TN, and Midwest Micro Lab, Indianapolis, IN. All reported
compounds gave satisfactory carbon and hydrogen analyses.
Due to the high nitrogen content and explosive nature of these
compounds, some reported microanalytical data for nitrogen
Ack n ow led gm en t. We gratefully acknowledge the
financial support of this work by the Office of Naval
Research (N00014-90-J -1661) and Program Officer Dr.
Richard S. Miller.
(18) For a relavent review, see: Gasco, A.; Boulton, A. J . Adv.
Heterocycl. Chem. 1981, 29, 251.
J O9608836