Highly Energetic, Low Sensitivity Aromatic Peroxy Acids

Article abstract of DOI:10.1002/chem.201502989

The synthesis, structure, and energetic materials properties of a series of aromatic peroxy acid compounds are described. Benzene-1,3,5-tris(carboperoxoic) acid is a highly sensitive primary energetic material, with impact and friction sensitivities similar to those of triacetone triperoxide. By contrast, benzene-1,4-bis(carboperoxoic) acid, 4-nitrobenzoperoxoic acid, and 3,5-dinitrobenzoperoxoic acid are much less sensitive, with impact and friction sensitivities close to those of the secondary energetic material 2,4,6-trinitrotoluene. Additionally, the calculated detonation velocities of 3,5-dinitrobenzoperoxoic acid and 2,4,6-trinitrobenzoperoxoic acid exceed that of 2,4,6-trinitrotoluene. The solid-state structure of 3,5-dinitrobenzoperoxoic acid contains intermolecular O-H?O hydrogen bonds and numerous N?O, C?O, and O?O close contacts. These attractive lattice interactions may account for the less sensitive nature of 3,5-dinitrobenzoperoxoic acid.

Full text of DOI:10.1002/chem.201502989

DOI: 10.1002/chem.201502989
Communication
&
Peroxides
Highly Energetic, Low Sensitivity Aromatic Peroxy Acids
Nipuni-Dhanesha H. Gamage,[a] Benedikt Stiasny,[b] Jçrg Stierstorfer,[b] Philip D. Martin,[a]
Thomas M. Klapçtke,*[b] and Charles H. Winter*[a]
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Abstract: The synthesis, structure, and energetic materials
properties of a series of aromatic peroxy acid compounds
are described. Benzene-1,3,5-tris(carboperoxoic) acid is
a highly sensitive primary energetic material, with impact
and friction sensitivities similar to those of triacetone tri-
peroxide. By contrast, benzene-1,4-bis(carboperoxoic) acid,
4-nitrobenzoperoxoic acid, and 3,5-dinitrobenzoperoxoic
acid are much less sensitive, with impact and friction sen-
sitivities close to those of the secondary energetic material
2,4,6-trinitrotoluene. Additionally, the calculated detona-
tion velocities of 3,5-dinitrobenzoperoxoic acid and 2,4,6-
trinitrobenzoperoxoic acid exceed that of 2,4,6-trinitroto-
luene. The solid-state structure of 3,5-dinitrobenzoperoxo-
ic acid contains intermolecular O-H···O hydrogen bonds
and numerous N···O, C···O, and O···O close contacts. These
attractive lattice interactions may account for the less sen-
sitive nature of 3,5-dinitrobenzoperoxoic acid.
Scheme 1. Synthesis of 1–4.
report the synthesis, structure, and energetic materials proper-
ties of four aromatic peroxy acids. Remarkably, three of these
compounds have low sensitivities, very high energy contents,
and have properties appropriate for application as secondary
energetic materials. These are the first peroxide-based com-
pounds that can be classified as secondary explosives. Structur-
al data point to stabilization of the labile oxygen–oxygen
bonds through hydrogen bonding and intermolecular N···O,
C···O, and O···O close contacts.
The compounds triacetone triperoxide (TATP), diacetone diper-
oxide (DADP), hexamethylene triperoxide diamine (HMTD), and
methyl ethyl ketone peroxide (MEKP) are the only peroxides
for which detailed energetic materials properties have been
determined.[1–3] These peroxides are extremely sensitive to
stimuli and are dangerous to handle.[1–3] Other issues include
a low decomposition temperature for HMTD (758C),[1a] high
volatilities for TATP and DADP,[1,2] and calculated detonation ve-
locities for TATP (6168 msÀ1), DADP (6773 msÀ1), and MEKP
(6191 msÀ1) that are much lower than those of high nitrogen
explosives such as RDX (8750 msÀ1) and HMX (9100 msÀ1).[1a]
These issues, particularly the high sensitivities, have prohibited
military and civilian energetic materials applications of TATP,
DADP, HMTD, and MEKP. Moreover, the high sensitivities have
likely limited more extensive exploration of peroxo compounds
as energetic materials. Peroxo-based compounds might serve
as useful explosives if their sensitivities can be adjusted to op-
timum levels for specific applications and also to allow safe
handling. A recent report demonstrated that co-crystals of
DADP and 1,3,5-triiodo-2,4,6-trinitrobenzene (TITNB) have re-
duced impact sensitivity compared to both pure DADP and
TITNB, because of I···O close contacts in the co-crystals.[4] We
have also recently described the synthesis, structure, and ener-
getic materials properties of oxygen-rich organic compounds
containing bis(hydroperoxy)-methylene groups that are less
sensitive than TATP, DADP, HTMD, and MEKP.[5] Herein, we
Peroxy acids 1–4 were prepared in high yields, as depicted
in Scheme 1. Compounds 3 and 4 were prepared by literature
procedures entailing treatment of the carboxylic acids with
84% H2O2 in the presence of methanesulfonic acid.[6] Com-
pounds 1 and 2 were prepared under similar conditions from
the acid chlorides and 84% H2O2.[7] Importantly, 1–4 precipitate
from the reaction solutions upon cooling to near 08C and can
be isolated as pure materials by filtration and subsequent air
drying. Minimal synthetic manipulation is a great advantage in
the synthesis of highly energetic compounds. Attempts to pre-
pare peroxy acids using the acid chlorides derived from
1,2,4,5-benzene tetracarboxylic acid and mellitic acid led to vi-
olent reactions upon addition of H2O2, and the desired com-
pounds could not be isolated. Compounds 1–4 were character-
1
ized with H and 13C NMR spectroscopy, infrared spectroscopy,
and elemental analyses.[7] Additionally, the X-ray crystal struc-
tures of 1·DMF and 4 were determined.[7] Crystals of 1·DMF
were used only for the X-ray experiment, whereas solvent-free
1 was used for all other measurements.
A perspective view of 4 is shown in Figure 1. The bond
lengths in 4 are normal. The density of 4 is 1.748 gcmÀ3 at
100 K, which is higher than those of orthorhombic
(1.704 gcmÀ3 at 123 K) and monoclinic (1.713 gcmÀ3 at 100 K)
2,4,6-trinitrotoluene (TNT).[8] Because the formula weights of 4
and TNT are almost identical, 4 packs more efficiently than TNT
in the solid state. TNT does not contain any strong hydrogen
bonds, and only van der Waals forces are present.[8] The asym-
metric unit of 4 consists of two molecules situated in an edge-
to-face fashion, with a close contact of 2.988 Š between an
oxygen atom of a nitro group in one molecule and the p-face
of a ring CÀH carbon atom in the other molecule. The lattice
contains intermolecular O-H···O hydrogen bonds, in addition to
numerous N···O (2.993–3.054 Š), C···O (3.043–3.215 Š), and O···O
(2.670–3.029 Š) close contacts that are within the van der
Waals radii for N···O (3.07 Š), C···O (3.22 Š), and O···O (3.04 Š).[9]
[a] N.-D. H. Gamage, Dr. P. D. Martin, Prof. Dr. C. H. Winter
Department of Chemistry
Wayne State University, Detroit
Michigan 48202 (USA)
E-mail: chw@chem.wayne.edu
[b] B. Stiasny, Dr. J. Stierstorfer, Prof. Dr. T. M. Klapçtke
Department of Chemistry
Ludwig-Maximilians University
Butenandtstr. 5–13 (D), 81377 München (Germany)
E-mail: tmk@cup.uni-muenchen.de
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201502989.
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Table 1. Sensitivities and energetic performance of 1 and 3–5.
1
3
4
5
Formula
FW [gmolÀ1
IS [J][a]
C8H6O6
198.14
10
288
0.1
À105.0
160
1.423
À584.1
À3373
88
C8H6O6
183.12
9
360
0.1
C7H4N2O7
228.11
9
360
0.1
À63.13
132
1.748
À310.9
À4660
213
C7H3N3O9
271.11
—
–
–
]
FS [N][b]
ESD [J][c]
WCO2 [%][d]
À100.5
À38.4
TDec [8C][e]
141
–
[f]
1 [gcmÀ3
]
1.586[m]
À324.3
À3590
133
1.80[n]
À275.5
À5243
269
DfH8 [kJmolÀ1
]
]
[g]
DExU8 [kJkgÀ1
[h,i]
PCJ [kbar][h,j]
VDet [msÀ1
]
5262
598
6176
628
7217
596
7885
619
[h,k]
Vo [LkgÀ1
]
[h,l]
[a] BAM drophammer. [b] BAM friction. [c] Electrostatic discharge sensitivi-
ty. [d] Oxygen balance for CO2. [e] Decomposition temperature from DTA
(58CminÀ1). [f] Density from X-ray diffraction for 1·DMF and 4 at À1738C.
[g] Calculated molar enthalpy of formation. [h] Calculated using
EXPLO5V6.02. [i] Total energy of detonation. [j] Detonation pressure.
[k] Detonation velocity. [l] Volume of detonation products. [m] Published
crystal density.[14] [n] Estimated density at 258C.
Figure 1. X-ray crystal structure of 4. Selected bond lengths (Š): O1ÀO2
1.447(3), O2ÀC1 1.342(4), O4ÀC1 1.196(4).
detonation performance values increase in going from 1 to 4.
The calculated detonation pressure (PCJ) range from 88 kbar for
1 to 213 kbar for 4. The calculated detonation velocities in-
crease from 5262 to 7217 msÀ1 for 1 and 4, respectively.
Recent studies of energetic materials have shown that such
close contacts are attractive because the dispersion forces are
larger than the repulsive Coulombic forces.[10] Dissociation en-
ergies of O···O close contacts are similar to those of weak hy-
drogen bonds (3–13 kJmolÀ1).[10] Accordingly, much of the lat-
tice energy in 4 arises from non-bonded interactions. Addition-
ally, these non-bonded attractive interactions contribute to the
high solid state density of 4.
The thermal behaviour of 1–4 was studied using thermogra-
vimetric analysis and differential thermal analysis. The com-
pounds show decomposition onsets ranging from 132 to
1608C (Table 1). A 200 mg sample of 4 was reported to ex-
plode just above its melting point of 112 8C.[6b] We observed
no explosions with 4 up to 1508C, but extreme care should be
used when handling this compound. CBS-4M electronic enthal-
pies were calculated with the Gaussian 09 software package to
obtain heats of formation values using the atomization equa-
tion.[11] The values are all exothermic, but 3 and 4 have the
most positive heats of formation.
The extremely high performance values and low sensitivity
of 4 prompted us to consider the more highly nitrated peroxy
acid 5. Synthetic approaches to 5 are ongoing, but the per-
formance parameters were calculated using EXPLO5.[14] Using
an estimated solid-state density of 1.80 gcmÀ3 based upon
those of 3[15] and 4, the calculated detonation pressure of 5 is
269 kbar and the calculated detonation velocity is 7885 msÀ1
.
The present work documents the energetic materials proper-
ties of peroxy acids 1–5. Com-
pound 2 is “very sensitive” and
“extremely sensitive” to impact
and friction, respectively, according
to the UN recommendations,[13]
with values that are in the same
range as those of TATP.[1,2] By con-
trast, 1, 3, and 4 are much less sen-
sitive than 2, TATP, DADP, HMTD,
Table 1 gives detailed energetic test results for 1 and 3–5.
Impact, friction, and sensitivity toward electrostatic discharge
were determined with a drop hammer, friction tester, and elec-
trostatic discharge tester, respectively, using standard Bunde-
sanstalt für Materialforschung und –prüfung (BAM) and elec-
trostatic methods.[12] Sensitivity classifications are based on the
“UN Recommendations on the Transport of Dangerous
Goods”.[13] Energetic performance was calculated using the
EXPLO5V6.02 software.[14] Compound 2 has an impact sensitivi-
ty of 1 J, a friction sensitivity of 5 N, and an electrostatic dis-
charge of 0.025 J.[7] This electrostatic discharge value is close to
what can be created by the human body (ꢀ0.02 J),[1b] so 2
must be handled with great care. Compounds 1, 3, and 4 have
impact sensitivity values of 10 (1) and 9 (3, 4) J and friction
sensitivity values of 288 (1) and 360 (3, 4) N. The calculated
and MEKP. According to the UN Recommendations,[13] 1, 3, and
4 are “sensitive” toward impact and “less sensitive” to “insensi-
tive” toward friction. These impact and friction sensitivity
values are very similar to those of TNT, which is a widely used
secondary explosive.[1] Hence, 1, 3, and 4 can also be classified
as secondary explosives. These are the first peroxide-based sec-
ondary explosives. Moreover, the detonation velocity of 4
(7217 msÀ1) exceeds that of TNT (6900 msÀ1). The detonation
velocity of 5 (7885 msÀ1) is much higher than those of 4 and
TNT, but is less than that of RDX (8750 msÀ1).[1] Hence, 4 and 5
are powerful explosives, which likely arises from higher solid-
state densities compared to TATP, DADP, HMTD, and MEKP.[1–3]
There is no single structural feature in 1, 3, and 4 that can ex-
plain their reduced sensitivities relative to 2, TATP, DADP, HMTD,
and MEKP. Low sensitivity, high energy explosives tend to pack
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in layered structures with hydrogen bonds within each layer,
but only weak van der Waals interactions between the layers.[10]
These materials can absorb shocks by allowing interlayer sliding
without covalent bond breaking.[10c] By contrast, high sensitivity,
high energy explosives tend to have structures that do not
allow facile dissipation of shocks, which leads to hot spots, co-
valent bond breaking, and explosions.[10b] Compound 3 contains
a wave-like packing arrangement,[7,15] which has been previously
proposed as a structural motif that allows shock dissipation in
low sensitivity, high energy explosives.[10c] The lattice of 3 con-
tains O-H···O hydrogen bonds, three O···O close contacts (2.740–
2.965 Š), and one N···O close contact (3.063 Š).[7,15] Examination
of the packing in 4 does not show a layered structure like those
observed in low sensitivity, high energy explosives.[10c] The low
sensitivity of 4 may arise from the presence of intermolecular
O-H···O hydrogen bonds and the numerous N···O (5 interac-
tions), C···O (5 interactions), and O···O (7 interactions) close con-
tacts, which stabilize the lattice and could allow dissipation of
shock without covalent bond breaking. In this vein, the reduced
sensitivity of DADP/TITNB co-crystals was proposed to originate
from attractive I···O close contacts that stabilize the covalent
oxygen–oxygen and iodine–carbon bonds.[4] As comparisons,
the solid-state structures of highly sensitive DADP and TATP
have no O···O close contacts, and contain only very weak O···H
and C···H interactions.[2b,7] Features in 3 and 4 that are lacking in
DADP and TATP include the O-H···O hydrogen bonding and the
N···O, C···O, and O···O close contacts. We propose that these
structural motifs stabilize the lattices and contribute to the low
sensitivities of 1, 3, and 4. In particular, the O···O close contacts
in 4 likely stabilize the labile oxygen–oxygen bonds and make
bond cleavage less favorable. The sterically unconstrained
nature of the oxygen and nitrogen atoms in peroxy acid and
nitro groups allows more intermolecular close contacts, relative
to the peroxo groups in DADP and TATP.
Keywords: explosives
sensitivities · structure elucidation
· hydrogen bonding · peroxides ·
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As a cautionary note, 4 has been suggested a “safe” oxygen
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actions.[6b] The highly energetic nature of 4 advises against its
large-scale synthesis. Finally, there is significant interest in the
development of high-energy dense oxidizers to replace ammo-
nium perchlorate.[1] Though the oxygen balances of 1–5 are all
negative (À105 to À38%) and ammonium perchlorate is posi-
tive (34%[1]), the present work suggests that incorporation of
peroxy acid groups in energetic materials structures can make
the oxygen balance more positive without increasing sensitivi-
ty and decreasing performance. It has been reported that the
active oxygen content of 4 is reduced from 93.5% to 84.0%
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´
[14] M. Suceska, EXPLO5V6.02 Program, Brodarski Institute, Zagreb, Croatia, 2014.
Acknowledgements
[15] H. S. Kim, S.-C. Chu, G. A. Jeffrey, Acta Crystallogr. Sect. A 1970, 26, 896–
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The authors acknowledge generous support from the Office of
Naval Research (Grant No. N00014-12-1-0526 to C.H.W., Grant
No. N00014-12-1-0538 to T.M.K.).
Received: July 30, 2015
Published online on January 7, 2016
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2585
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim