Preparation and Characterization of trans-1,4-Diazido-1,4-dinitrocyclohexane and exo-2,5-Diazido-endo-2,5-dinitronorbornane: Stable Geminal Azido-Nitro Compounds

Full text of DOI:10.1021/jo9620268

1
872
J . Org. Chem. 1997, 62, 1872-1874
chemically.8 This compound showed propensity to dis-
P r ep a r a tion a n d Ch a r a cter iza tion of
tr a n s-1,4-Dia zid o-1,4-d in itr ocycloh exa n e
place a nitro group and form the highly unstable diazido
derivative under electrochemical conditions. As part of
our efforts to synthesize molecules of high nitrogen
content, we have synthesized and fully characterized
various carbon ring systems containing the gem-azido-
nitro functionality.
a n d
exo-2,5-Dia zid o-en d o-2,5-d in itr on or bor n a n e:
Sta ble Gem in a l Azid o-Nitr o Com p ou n d s
G. K. Surya Prakash,* J ohn J . Struckhoff, J r.,
Klaus Weber, Andre Schreiber, Robert Bau, and
George A. Olah*
Resu lts a n d Discu ssion
5
As noted previously, we have synthesized cyclic gemi-
Loker Hydrocarbon Research Institute and Department of
Chemistry, University of Southern California,
Los Angeles, California 90089-1661
nal dinitro compounds using methodology developed by
Kornblum and co-workers for oxidative substitution of
nitroparaffin salts.9 We endeavored to use this same
protocol for the synthesis of molecules containing geminal
azido-nitro functionality. All starting secondary nitro
compounds used in this study were prepared according
Received October 29, 1996
In tr od u ction
5
to previously discussed methods, and in all cases yields
were comparable or slightly improved. 1,3,5-Trinitroben-
zene (1) was reduced using sodium borohydride in aque-
ous methanol10 to give 1,3,5-trinitrocyclohexane (2) as a
mixture of isomers (Scheme 1).
The development of methods for the synthesis of novel
compounds that combine properties of high energy, high
density, and high stability is a continuing effort in
1
energetic materials research. Cyclic nitramines such as
Substitution at saturated carbons by means of electron-
transfer reactions via radical anionic intermediates is
long established.11 Salts of secondary aliphatic nitro
compounds readily undergo oxidative substitution to give
the geminal substituted products.
cyclotrimethylenetrinitramine (RDX) and cyclotetra-
methylenetetranitramine (HMX) have been in practical
use since World War II.2 Recent achievements in this
field are highlighted by the synthesis of 1,3,3-trinitroaze-
3
tidine (TNAZ) , a four-membered cyclic nitramine con-
taining geminal dinitromethylene unit, and condensa-
tions affording the hexaazaisowurtzitane skeleton and
its subsequent conversion to the hexanitro derivative
(
HNIW).4 In addition to work done on the synthesis of
cyclic nitramines, recent efforts have focused on the
development of methodologies to produce compounds
containing novel functionalities of potential energetic
This method works well for the synthesis of R-substi-
tuted nitriles, sulfones, and even for the synthesis of gem-
dinitro compounds. The great advantage of this method
is that it relies on the use of the relatively inexpensive
potassium ferricyanide as a one-electron oxidant versus
5
interest, most notably the geminal dinitro group and
mono- and gem-difluoroamino groups.6
Bowman and co-workers found in a mechanistic in-
vestigation that oxidative addition of azide to the anions
of secondary nitroalkanes proceeded to give the R-sub-
stituted azido-nitro compound.7 They were able to
prepare both 1-azido-1-nitrocyclohexane and 2-azido-2-
nitropropane. However, these compounds were only
isolable via distillation and were not amenable to other
means of purification. Additionally, they state that
longer reaction times and excess amounts of azide result
in loss of the nitro group to give the secondary diazide.
Wagner and Weber also encountered difficulty in at-
tempts to synthesize 1-azido-1,1-dinitroethane electro-
9
other methods involving more expensive silver salts.
We have been able to extend the use of this methodol-
ogy of Kornblum for the synthesis of stable, isolable
geminal azido-nitro compounds. For example, 1-azido-
1-nitrocyclohexane (4) was prepared from nitrocyclohex-
ane using sodium azide and potassium ferricyanide
(Scheme 2).
Compound 4 was identified by its characteristic 13C
resonance at 103.1 ppm for C1 and by its infrared
-
1
absorption bands at 2212 and 1552 cm , which is
7
consistent with the data found by Bowman et al.
(1) Nielsen, A. T. Polycylic Amine Chemistry. In Chemistry of
However, the oily product was not amenable to mass
spectrometric analysis or purification by column chro-
matography. Spontaneous decomposition with evolution
of gases resulted when 4 came in contact with silica
gel, and the only product isolated was cyclohexanone.
Despite the difficulties encountered in purification, we
were encouraged by this result. We further investigated
the utility of using this methodology on cyclic secondary
di- and trinitro compounds to synthesize molecules with
high nitrogen content. Similar to the above reaction, 1,4-
Energetic Materials; Olah, G. A. Squires, D. R., Eds.; Academic Press,
Inc.: New York, 1991; pp 95-124.
(2) Urbanski, T. Chemistry and Technology of Explosives; Pergamon
Press: Oxford, 1967; Vol. III, Chapter IV.
3) (a) Archibald, T. G.; Gilardi, R.; Baum, K.; George, C. J . Org.
(
Chem. 1990, 55, 2920. (b) Katritzky, A. R.; Cundy, D. J .; Chen, J . J .
Heterocycl. Chem. 1994, 31, 271. (c) Marchand, A. P.; Rajagopal, D.;
Bott, S. G.; Archibald, T. G. J . Org. Chem. 1995, 60, 4943. (d) Axenrod,
T.; Watnick, C.; Yazdekhasti, H.; Dave, P. R. J . Org. Chem. 1995, 60,
1
959.
4) (a) Nielsen, A. T.; Nissan, R.; Vanderah, D. J .; Coon, C.; Gilardi,
R.; George, C. F.; Flippen-Andersen, J . L. J . Org. Chem. 1990, 55, 1459.
b) Miller, R. S. Research on New Energetic Materials. In Decomposi-
(
(
tion, Combustion, and Detonation Chemistry of Energetic Materials;
Brill, T. B., Russell, T. P., Tao, W. C., Wardle, R. B., Eds.; Materials
Research Society: Pittsburgh, PA, 1996; Vol. 418, p 3-14.
(8) Wagner, R.; Weber, J . Personal communication from efforts
carried out at Rocketdyne, Inc., in 1984-85.
(9) Kornblum, N.; Singh, H. K.; Kelly, W. J . J . Org. Chem. 1983,
48, 332 and references therein.
(
5) Olah, G. A.; Ramaiah, P.; Prakash, G. K. S.; Gilardi, R. J . Org.
Chem. 1993, 58, 764.
(
6) See ref 4b.
(10) (a) Severin, T.; Schmitz, R. Chem. Ber. 1962, 95(6), 1417. (b)
Atroshchenko, Yu.M.; Nasonov, S. N.; Gitis, S. S.; Kaminskii, A. Ya.;
Mel’nikov, A. I.; Shakhkel’dyan, I. V. Zh. Org. Khim. 1994, 30, 675.
(11) Kornblum, N. Angew. Chem., Int. Ed. Engl. 1975, 14, 734.
(7) (a) Al-Khalil, S. I.; Bowman, W. R.; Symons, M. C. R. J . Chem.
Soc., Perkin Trans. 1 1986, 555. (b)Al-Khalil, S. I.; Bowman, W. R.
Tetrahedron Lett. 1982, 23, 4513.
S0022-3263(96)02026-9 CCC: $14.00 © 1997 American Chemical Society

Notes
J . Org. Chem., Vol. 62, No. 6, 1997 1873
Sch em e 1
Sch em e 2
Sch em e 3
F igu r e 1. Molecular plot of trans-1,4-diazido-1,4-dinitrocy-
clohexane (6b). A crystallographic center of symmetry is
situated in the middle of the molecule.
Sch em e 5
Sch em e 4
unstable.12 Additionally, 1,3-dinitrotetramethycyclobu-
tane proved unreactive under these conditions, and no
gem-azido-nitro products were found. This is consistent
dinitrocylcohexane (5) undergoes oxidative azidation to
give 1,4-diazido-1,4-dinitrocyclohexane (6a and 6b) in
with prior work done in our group in attempts to
synthesize the geminal dinitro compound.5 Finally,
treatment of isomeric trinitrocyclohexane 2 with aqueous
sodium hydroxide resulted in a black solution that was
not amenable to this present methodology.
8
5% overall yield as a mixture of cis and trans isomers
(see Scheme 3).
Recrystallization from warm ethyl acetate yielded
solely the stable trans isomer as crystalline white needles
that decomposed above its melting point of 138 °C. The
structure of 6b was confirmed by proton and carbon
NMR, as well as by single-crystal X-ray diffraction
analysis (vide infra).
Both trans-1,4-diazido-1,4-dinitrocyclohexane (6b) and
exo-2,5-diazido-2,5-endo-dinitronorbornane (8b) represent
new, stable energetic compounds of substantial interest.
It is important to note that we found no evidence for
further displacement of a nitro group when using excess
amounts of sodium azide in the preparation or even when
reactions were stirred overnight. Recrystallization was
found to be the only suitable method for isolation in pure
form. The pure crystalline compounds (6b and 8b) were
used in single-crystal X-ray diffraction structure deter-
minations.
Similarly, 2,5-dinitronorbornane (7) was oxidatively
converted to 2,5-diazido-2,5-dinitronorbornane (8a and
8
b) in 72% yield as a mixture of exo-2-azido-endo-5-azido
(8a ) and exo-2-azido-exo-5-azido (8b) isomers (Scheme 4).
It is important to note that no evidence was found for
a product with the endo-2-azido-endo-5-azido arrange-
ment, presumably due to the hindered nature of the endo
face of the norbornane skeleton. Recrystallization, again
from warm ethyl acetate, yielded pure 8b, which was
Compound 6b crystallizes in the monoclinic space
group P2
1
/n, with a ) 5.988(2) Å, b ) 13.791(2) Å, c )
6
.616(2) Å, â ) 105.81(2)°, Z ) 2. Data were collected at
1
13
fully characterized by H and C NMR and X-ray
crystallography (vide infra). This compound has a melt-
ing point of 94-96 °C, and it decomposes upon further
heating above 100 °C.
-100 °C on a Siemens P4/RA X-ray diffractometer with
Cu KR radiation up to a 2θ maximum of 102.5°. The
structure was solved with direct methods and refined to
a final agreement factor of R ) 5.3%. The molecule,
shown in Figure 1, is situated on a crystallographic center
of symmetry. The two azide groups are axial, and the
nitro groups are equatorial. The bond between the
carbon of the ring and the nitrogen of the azide group is
Further work on oxidative azidation of other ring
systems, however, proved to be less successful. When
the dianion of 9 was treated with sodium azide and
1
3
potassium ferricyanide, NMR showed C resonances
between 108 and 110 ppm, indicative of the formation of
the geminal azido-nitro species (Scheme 5).
6
(12) A 15 mg sample used for NMR analysis in DMSO-d built up
However, no isolation of any of the isomeric products
via recrystallization was achieved as they proved to be
considerable pressure, and gas evolved when the cap of the tube was
removed after analysis.

1
874 J . Org. Chem., Vol. 62, No. 6, 1997
Notes
-N
point of attachment to the carbon framework [C
) 114.9(5)°, C -N -N ) 115.0(5)°], but the azide
groups themselves are linear [N -N -N ) 171.5(6)°,
-N -N
) 171.7(7)°].13
2
4
-
N
5
5
1
2
1
2
3
N
4
5
6
Exp er im en ta l Section
3 6 2 2
NMR spectra were recorded in CDCl , DMSO-d , or CD Cl
at 200 or 300 MHz. FT-IR spectra were obtained either as KBr
pellets or as neat films on NaCl plates. Melting points were
not corrected. Starting materials were obtained from Aldrich
and used without purification, except for 1, which was purchased
from Tokyo Kasei Kogyo Co. All secondary nitro compounds
were prepared from the corresponding oximes according to
previously reported methods.5
Caution: Outside of the difficulties encountered with 10, all
other isolated materials were stable. All reactions were per-
formed behind a safety shield in the dark, and all isolated
compounds were stored in a freezer. Both isolated crystalline
compounds 6b and 8b were subjected to a hammer test on 20-
3
0 mg samples wrapped in aluminum foil and showed no
reaction. How ever , w or k in g w ith a zid es is in h er en tly
d a n ger ou s a n d fu ll sa fety p r eca u tion s m u st be ta k en .
Ad d ition a lly, th e biologica l toxicity of th is gem in a l fu n c-
tion a l gr ou p in g is u n k n ow n , bu t sh ou ld be r ega r d ed a s
su bsta n tia l.
P r ep a r a tion of tr a n s-1,4-Dia zid o-1,4-d in itr ocycloh ex-
a n e (6b). 1,4-Dinitrocyclohexane (5), 0.52 g, was added to a
solution of NaOH (0.24 g, 2 equiv) in 12 mL of water and stirred
under argon for 5.5 h (until all solid had dissolved). This solution
was then added dropwise under argon to a solution of K
CN) (9.83 g, 10 equiv) and NaN (3.89 g, 20 equiv) in 50 mL of
water and 15 mL of CH Cl at ice temperature that was
3
Fe-
(
6
3
2
2
protected from light. The solution was stirred at this temper-
ature for 3 h and then stirred at room temperature overnight.
The reaction was poured into a separatory funnel, and the
organic layer was drawn off. Solid NaCl was added to the
F igu r e 2. Packing diagram of 6b in the crystalline state,
showing interactions between the azide and nitro groups of
adjacent molecules.
aqueous layer, and it was extracted with 3 × 30 mL of CH
The extracts were combined and dried with MgSO , and the
solvent was removed under reduced pressure to yield 0.65 g
85.0%) of a yellow/white solid. NMR of the crude material
2 2
Cl .
4
(
indicated a 60:40 mixture of trans:cis isomers, of which the trans
isomer (6b) could be separated by recrystallization from warm
(
50 °C) ethyl acetate, forming fine white needles: mp 138 °C
1
dec; H NMR (benzene-d
6
) δ 1.38 (d, 4H, J ) 9.4 Hz), 1.72 (d,
) δ 29.06 (t), 100.58 (s); IR
KBr) 2127 (vs), 1543 (vs) cm . Anal. Calcd for C : C,
8.13; H, 3.15; N, 43.74. Found: C, 28.18; H, 2.97, N, 43.91.
4
(
2
H, J ) 9.4 Hz); 13C NMR (DMSO-d
6
-
1
6 8 8 4
H N O
3
Density: 1.62 mg/mm (from X-ray measurement).
P r ep a r a t ion of tr a n s-2,5-Dia zid o-2,5-d in it r ob icyclo-
[
2.2.1]h ep ta n e (8b). This product was obtained in a similar
manner to 6 in 72% yield. Recrystallization could be achieved
from warm ethyl acetate to yield 8b, which has a mp of 94-96
F igu r e 3. Molecular plot of exo-2,5-diazido-endo-2,5-dinitroni-
tronorbornane (8b). A noncrystallographic 2-fold rotation axis
°
C: 1H NMR (CD
endo, H
ddd, 2H, H
2
Cl
endo, J endo-exo ) 16.1 Hz), 2.16 (m, 2H, H
exo, H
2
) δ 3.06 (dt, 2H, H
1
and H
4
), 2.49 (dt, 2H,
), 2.06
exo, J exo-endo ) 16.1 Hz, J 3-4 ) 5.86 Hz);
H
3
6
7
is present vertically through atom C
distinctly bent [C -N -N ) 114.8(4)°], consistent with
sp hybridization, while the N -N -N angle is linear
171.5(5)°] as expected. Figure 2 shows a portion of the
7
.
(
3
6
1
3
1
2
3
C NMR (CD
2
Cl
2
) δ 34.48, 37.45, 46.13, 106.63; IR (KBr) 2122
2
-1
7 8 8 4
(vs), 1559 (vs) cm . Anal. Calcd for C H N O : C, 31.35; H,
2
3
4
3
1
.01; N, 41.78. Found: C, 31.58, H, 3.10, N, 42.44. Density:
.58 mg/mm3 (from X-ray measurement).
[
intermolecular packing in the crystal, which features
some interactions between azido and nitro groups of
neighboring molecules.
Ack n ow led gm en t. Support for our work by the
Compound 8b crystallizes in the triclinic space group
P1 with a ) 6.554(3) Å, b ) 7.030(5) Å, c ) 13.568(5) Å,
R ) 78.37(4)°, â ) 80.85(3)°, γ ) 67.94(4)°, Z ) 2. Data
were collected as described above at room temperature
and the structure refined to a final R factor of 6.7%. The
structure, shown in Figure 3, shows a noncrystallo-
graphic 2-fold rotation axis passing through the bridge-
Office of Naval Research (Program Manager: Richard
S. Miller) is gratefully acknowledged. A.S. wishes to
thank the Feodor Lynen Foundation for financial support.
J O9620268
(13) The author has deposited atomic coordinates for this structure
with the Cambridge Crystallographic Data Centre. The coordinates
can be obtained, on request, from the Director, Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK.
head atom (C
7
), bisecting the angle C
1
-C
7
4
-C . As in the
case of compound 6b, the azide ligands are bent at the