Polynitramino compounds outperform PETN

Article abstract of DOI:10.1039/b916909a

New polynitramino compounds were synthesized and fully characterized using IR and multinuclear (¹H, ¹³C, ¹⁵N) NMR spectroscopy, and elemental analysis as well as single-crystal X-ray diffraction.

Full text of DOI:10.1039/b916909a

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Polynitramino compounds outperform PETNw
Young-Hyuk Joo and Jean’ne M. Shreeve*
Received (in Cambridge, UK) 17th August 2009, Accepted 12th October 2009
First published as an Advance Article on the web 2nd November 2009
DOI: 10.1039/b916909a
New polynitramino compounds were synthesized and fully
characterized using IR and multinuclear (1H, 13C, 15N) NMR
spectroscopy, and elemental analysis as well as single-crystal
X-ray diffraction.
obtained in good yield. The structure of 4 was verified by
single-crystal X-ray diffraction analysis (Fig. 1).z Efforts to
nitrate urethane 2 did not yield the tetranitro derivative 3
when treated with only 100% nitric acid.
Other successful syntheses of polynitramines 5 (77%), which
was proved by single crystal X-ray diffraction analysis (Fig. 1),
6 (79%) and 7 (90%) by analogous nitration of polyurethane
derivatives with concomitant retention of the pentaerythritol
system resulted from extension of this reaction (Scheme 2).
The structures of all polynitramine derivatives 4–7 are
supported by 1H, 13C and 15N NMR spectroscopic data
(Table 1).
Various energetic compounds have been investigated as
precursors of high density energetic nitrimino,1 nitramino,2
nitro,3 or nitrato1a,3c,d compounds. In particular, high-energy
polyazapolycyclic caged polynitramines have emerged as a
promising family of high-energy density materials.2d The
current well known polynitramino compounds are RDX,
HMX and CL-20.
Primary nitramine molecules [dinitrourea (DNU),4 methylene
dinitramine (MDNA)5 and ethylene dinitramine (EDNA)6]
have impressive high densities, positive oxygen balances
(except EDNA) and good detonation properties. However,
the application of primary nitramines as energetic materials
is limited due to their relatively low thermal stability
(for DNU:4c Tdec.: 92 1C, for MDNA:5 Tdec.: 98–101 1C).
Thermal decomposition studies involving aliphatic primary
nitramines have led to an understanding of the relationship
between structure and thermostability, and to the suggestion
of a decomposition mechanism for these compounds.7a,b
Increasing the number of nitro groups in a molecule in order
to obtain a more balanced and powerful explosive inevitably
results in an increase in acidity and a decrease in thermal
stability of the resulting compounds.7
The preparation of an asymmetric tetranitramine 11 was
attempted by analogous nitration of the asymmetric
tetraurethane 8 (Scheme 3; also see ESIw, Scheme S1). When
the latter was nitrated with 100% nitric acid in trifluoroacetic
anhydride, only
a trinitro-substituted carbamate 9 was
obtained as a colorless oil in a yield of 96%. Incomplete
substitution of nitro groups results from steric hindrance of
the three nitro urethane groups; this is significantly different
from methylene bridged nitro urethane 3. The reaction of the
asymmetric nitramine 10 with excess hydrazine hydrate in
ethanol provided a further approach to the trihydrazinium
salt (see ESIw).
The 15N NMR spectra9 of the polynitramines measured in
[D6]DMSO show two or four resonances for nitrogen of NO2
and NH (see ESIw). In the spectra, a typical chemical shift for
NO2 is observed between ꢀ23.1 and ꢀ17.8 ppm. The nitrogen
signals from NH are found between ꢀ207.6 and ꢀ195.7 ppm
at higher field than the starting material of polynitrourethane
(between ꢀ167.8 and ꢀ173.0 ppm) and lower field than
Here we describe the synthesis of a new energetic penta-
erythrityl tetranitramine (PETNA) 4 that is a colorless crystal
at ambient temperature, thermally decomposes at 183 1C, and
has high density. Also described are the chemical, thermal,
and sensitivity properties of 4, as well as some preliminary
calculated detonation properties.
Pentaerythrityl tetranitramine (PETNA) 4 was prepared
from pentaerythritol in overall good yields. Pentaerythrityl
tetraurethane 2, prepared from aqueous tetraamine 18 and
ethyl chloroformate, was nitrated using 100% nitric acid in
trifluoroacetic anhydride to form tetranitrourethane 3. The
latter was converted into 4 by ammonolysis with aqueous
ammonia at 90 1C (Scheme 1). Within two hours, the ester
groups were removed and the water-soluble ammonium salt
was formed. After hydrolysis with concentrated hydrochloric
acid, tetranitramine 4 was extracted with ethyl acetate and
Department of Chemistry, University of Idaho, Moscow,
ID 83844-2343, USA. E-mail: jshreeve@uidaho.edu;
Fax: +1 208 885 9146; Tel: +1 208 885 6215
w Electronic supplementary information (ESI) available: The experi-
mental procedures, analytical data, and NMR spectra of products.
CCDC 737611 (4) and 737612 (5). For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/b916909a
Scheme 1 Synthesis of pentaerythrityl tetranitramine (PETNA) 4;
A: H2–Pd/C, B: ClCOOCH2CH3, C: 100% HNO3–(CF3CO)2O,
D: 28% aq. NH3–36% HCl.
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Scheme 3 Attempt to synthesize asymmetric tetranitramine 11; A:
100% HNO3–(CF3CO)2O, B: 28% aq. NH3–36% HCl.
polyurethane with respect to the electronegativity effect
(see 15N NMR spectra for polynitrourethane in the ESIw).
The thermal behavior of 4–7, which have decomposition
temperatures between 181 and 185 1C (PETN: 160 1C, NG:
50–60 1C), was investigated using differential scanning calori-
metry (Table 2). Only tris(nitramino)propane (5) shows a
melting point (133 1C). Calculation of the heats of formation
for polynitramines 4 and 5 was accomplished by using
the Gaussian 03 suite of programs.10 The geometric optimiza-
tions of the structures and frequency analyses were carried
out by using the B3LYP functional with the 6–31+G**
basis set, and zero-point energies were calculated at the
MP2/6–311++G** level.
Fig.
1 Molecular structures (thermal ellipsoids represent 50%
probability) of 4 (top) and 5 (bottom). Selected bond lengths [A]
and angles [1]: 4: C1–C2 1.5417(12), C2–N3 1.4598(16), N3–N4
1.3327(15), N4–O6 1.2263(15), N4–O5 1.2379(14), C1–C2–N3
114.39(9), C2–N3–N4 122.37(10); 5: C(1)–C(2) 1.5318(17), C2–N3
1.4463(18), N3–N4 1.3262(18), N4–O6 1.2230(17), N4–O5 1.2279(19),
C1–C2–N3 113.74(12), C2–N3–N4 121.61(12).
All of the polynitramines exhibit negative heats of
formation with 4 and 5 having the least negative ꢀ0.193 and
1.450 kJ gꢀ1 (PETN: ꢀ1.590 kJ gꢀ1, NG: ꢀ1.548 kJ gꢀ1). The
detonation parameters [pressures (P) and velocities (D)] were
calculated using the CHEETAH 5.0 computer program.13
The program is based on the traditional Chapman–Jouget
thermodynamic detonation theory. For 4 and 5 the calculated
detonation pressures are 31.59 and 35.62 GPa (PETN:
31.39 GPa, NG: 25.3 GPa). Detonation velocities are
8657 and 8933 m sꢀ1, respectively (PETN: 8564 m sꢀ1, NG:
7700 m sꢀ1). The impact sensitivity was tested according
to BAM methods (BAM Fallhammer).14 In Table 1, there is
a range in impact sensitivities from the sensitive 4 (6 J) to 5
(20 J) and finally to the insensitive compound 6 (440 J)
and 7 (440 J). The sensitivity of these polynitramino
compounds is greatly reduced compared to PETN (2.9 J)
and NG (0.2 J).
Scheme 2 New polynitramines.
Table 1 Selected physical data of polynitramine compounds 4, 5, 6 and 7a
1
4: colorless crystal; H NMR: d = 3.63 (s, 8H), 12.02 (s, 4H, NH); 13C NMR: d = 42.2, 46.4; 15N NMR: d = ꢀ207.6, ꢀ23.1.
1
2
3
2
3
5: white crystal; H NMR: d = 3.49 (dd, J = 14.7 Hz, J = 8.3 Hz, 2H), 3.74 (dd, J = 14.7 Hz, J = 4.5 Hz, 2H), 4.47 (m, 1H), 12.20
(s, 3H, NH); 13C NMR: d = 44.4, 51.4; 15N NMR: d = ꢀ202.1, ꢀ195.7, ꢀ19.6, ꢀ18.5.
6: white crystal; 1H NMR: d = 3.27 (s, 4H), 3.60 (s, 12H), 11.80 (br s, 6H, NH); 13C NMR: d = 44.0, 46.1, 70.5; 15N NMR: d = ꢀ202.3, ꢀ18.0.
7: white solid; 1H NMR: d = 3.26 (s, 4H), 3.60 (s, 16H), 11.94 (br s, 8H, NH); 13C NMR: d = 43.7, 44.9, 45.7, 46.0, 70.5; 15N NMR: d = ꢀ202.1,
ꢀ201.9, ꢀ18.0, ꢀ17.8.
a 1H, 13C and 15N NMR (CH3NO2 as external standard) spectra were recorded (using [D6]DMSO as solvent) at 300.1 MHz, 75.5 MHz and
50.7 MHz, respectively. The data for all compounds are summarized in the ESI.w
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Table 2 Physical properties of polynitramines 4 and 5 comparing with PETN, NG and RDX
Compd
Tda/1C
Densityb/g cmꢀ3
DfH1298c/kJ molꢀ1 (kJ gꢀ1
)
Pd/GPa
De/m sꢀ1
ISf/J
OPg (%)
4
5
183
1.778
1.753i
1.778
1.60
ꢀ60.3 (ꢀ0.193)
324.9 (1.450)
ꢀ502.8 (ꢀ1.590)
ꢀ351.5 (ꢀ1.548)
92.6 (0.42)
31.59
35.62
31.39
25.3
8657
8933
8564
7700
8977
6
20
2.9
0.2
7.4
41
43
61
63
43
183h
160
PETNj
NGk
RDXj
50–60
230
1.816
35.17
a
b
c
Thermal decomposition temperature under nitrogen gas (DSC, 10 1C minꢀ1). Gas pycnometer (25 1C). Heat of formation (using
83.68 kJ molꢀ1 for the enthalpy of sublimation for each compound; calculated via Gaussian 03). Calculated detonation pressure
e
(CHEETAH 5.0). Calculated detonation velocity (CHEETAH 5.0). Impact sensitivity (BAM Fallhammer). OP = oxygen percent. 5 has
d
f
g
h
i
j
melting point at 133 1C. Determined by X-ray crystallography (20 1C). PETN = pentaerythrityl tetranitrate, RDX = 1,3,5-trinitro-1,3,5-
triazacyclohexane, ref. 3c and 11. NG = nitroglycerine, ref. 11 and 12.
k
Safety precautions: while we have experienced no difficulties
with the shock instability of polyazide and polynitramino
compounds, manipulations must be carried out in a hood
behind a safety shield. Leather gloves must be worn.
The authors gratefully acknowledge the support of DTRA
(HDTRA1-07-1-0024), NSF (CHE-0315275), and ONR
(N00014-06-1-1032). We are grateful to Dr D. A. Parrish,
Naval Research Laboratory (NRL), for determining the
single-crystal X-ray structures.
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z Crystallographic data compound 4: C5H12N8O8, Mr = 312.23,
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This journal is The Royal Society of Chemistry 2010
144 | Chem. Commun., 2010, 46, 142–144