Journal of Scientific & Industrial Research
Vol. 73, July 2014, pp. 485-488
Synthesis of some Potential High Energy Materials using Metal Nitrates; An
approach towards Environmental Benign Process
Ananta Saikia1*, Renganathan Sivabalan2, Girish M. Gore1 and Arun K. Sikder1
1
High Energy Materials Research Laboratory, Pune-411021, India
Combat Vehicles Research and Development Establishment, Chennai-600054, India
2
Received 14 December 2012; revised 18 October 2013; accepted 05 March 2014
A novel and efficient method for the synthesis of various promising high energy materials (HEMs) like nitrotriazolone
(NTO), 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), bis (2,2-dinitropropyl) nitramine (BDNPN),
1,1-diamino-2,2-dinitro ethylene (FOX-7) etc. using metal nitrates/sulphuric acid as nitrating agent has been described
successfully. The synthesized materials have been characterized using various spectroscopic techniques as well as thermal
studies and the data obtained confirmed their structure. From the study it was revealed that this method certainly an
alternative method of preparation of high energy materials (HEMs) in place of the conventional nitration mixture.
Keywords: Nitration, Metal nitrates, Insensitive, High Energy Materials
Introduction
The mission for novel high energy materials
(HEMs) with highest possible performance and
low vulnerability led to the development of
advanced insensitive power packed materials1-7 such
as triaminotrinitrobenzene (TATB), nitrotriazolone
(NTO), dinitrotetraoxa diazatetracyclo dodecance
(TEX), 1,1-diamino-2,2-dinitro ethylene (FOX-7),
2,4, 6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowur
tzitane (CL-20) and 2, 6-diamino-3, 5-dinitropy
razine-N-oxide (LLM-105). Many of these insensitive
HEMs are at various stages of pilot plant production
in different countries. However, the synthesis of
HEMs by the conventional methods led to formation
of large quantity of toxic liquid and gaseous wastes.
Due to this all over the globe research and
development programs are to produce HEMs without
leaving any toxic wastes.
In present work, we are reporting an alternative
nitration method for the synthesis of various
important high energy materials such as NTO,
FOX-7, BDNPN [bis (2,2-dinitropropyl) nitramine],
4-NI (4-nitroimidazole), CL-20 etc. which are the
energetic molecules from important class of futuristic
ingredients for insensitive munitions (IMs) with
superior performance. Nitration is one of the most
important reaction steps during the synthesis of
——————
*Author for correspondence
Email: [email protected]
HEMs. Conventional nitration processes generates
lots of acid wastes creating environmental pollution.
Apart from pollution, the other problems associated
with the use of conventional nitrating agent is that, if
the substrate molecule is deactivated due to presence
of strong electron withdrawing groups such as NO2,
C=O and SO2 (attached to nitrogen or carbon or
oxygen) the conventional nitration fails. Even if the
nitration of deactivated substrates is carried out under
harsher conditions using conventional nitrating
agents, the yields and purity of the product (s) are
poor. Another fate for the failure of nitration is
stability of substrates and their intermediates involved
in strong acidic conditions. To overcome these
drawbacks, the use of certain novel catalytic
materials, based on metal oxides, zeolites, inorganic
metal triflorates8 in association with conventional
nitrating agents has introduced a novel approach.
However, the information available on the use of
conventional nitrating agents in presence of novel
catalytic materials is scanty.
The selection of a nitrating agent for a particular
nitration reaction is mainly dependent on the type of
substrate molecule being nitrated. Most commonly
used nitrating agent is the mixture of concentrated
nitric acid and sulphuric acid. Conventionally used
nitrating agents pose serious threat of pollution,
thereby necessitating efficient and costly effluent
treatment. An alternative approach is sought for the
synthesis of HEMs using new nitrating agents.
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J SCI IND RES VOL 73 JULY 2014
Recently, some new nitration methods and
new nitrating agents have been developed, which
can be used under mild conditions. The salts of
nitronium ions, NO2BF4 and NO2PF6, N2O5, solids
as catalysts or as supports for other reagents,
Clay-DNPO, small-pore zeolite, H-ZSM-5 are being
used for the nitration of various organic compounds9-11.
Application of inorganic nitrates Bi(NiNO3)3, CAN,
NaNO3, KNO3, Ca(NO3)2, LiNO3 etc. for the nitration
of aromatic compounds have already been reported12-19.
Considering the importance of above mentioned
HEMs, we have attempted the synthesis of these
molecules using a novel and alternate method keeping
in mind the concept of environmental benign
approach. We are reporting here the use of inorganic
nitrates like potassium nitrate (KNO3), sodium nitrate
(NaNO3) and silver nitrate (AgNO3) with sulphuric
acid (H2SO4) as mild nitrating agents for the selective
nitration.
Experimental
Materials and Methods
All the reagents and chemicals used in the present
study were of AR grade and used as such. The
synthesized compounds were characterized by their
melting points and were uncorrected. IR spectra were
recorded (KBr pellets) on Shimmadzu FTIR-8400
Spectrophotometer. 1H -NMR spectra were recorded on
Varian Mercury Spectrometer at 300 MHz using TMS
as internal standard. DSC studies were undertaken on a
Perkin Elmer DSC-7 instrument operating at heating rate
10°C/min in nitrogen atmosphere with 1 mg of sample.
Elemental analysis was carried out with a CE Instrument
(Model CHN-1110). [Caution: All the synthesized
compounds described here are energetic materials.
Appropriate safety precautions were taken while
carrying out the reactions].
General procedure for the synthesis of insensitive high
explosives
Required quantity of concentrated sulfuric acid
(98 %) was taken in two necked round bottom flask
and cooled to 5C. Metal nitrate was added portion
wise to the sulphuric acid under stirring by keeping
the temperature bellow 10ºC. The substrate was added
to the nitrating mixture at 10ºC under continuous
stirring for about 30 minutes. The temperature of the
reaction mixture was allowed to rise to desired
temperature and further stirred for 2 to 4 hours
(the quantity of reactants and substrates along
with their reaction conditions are listed in Table 1).
After completion of the reaction (monitored by
TLC technique), reaction mixture was allowed to
attain room temperature. Then, the reaction mixture
was poured in to crushed ice (50 g) and stirred to
enhance the precipitation. The solid precipitate was
filtered and washed with minimum quantity of cool
water. The products were dried in a water-jacketed
oven at 50°C.
Table 1—Reaction details of synthesized compounds
Substrate
1,2,4-Triazolone
(TO) (0.5g, 0.0059mol)
Product Duration
(hrs)
NTO
2
Bis-2,2-dinitopropylamine BDNPN
(BDNPA)
(1g, 0.0036 mol)
2
Temp. Reagents used and yield (%)
(C)
45-50
H2SO4 (98%) (20 ml) H2SO4 (98%) (20 ml)
NaNO3 (0.63g,
KNO3 (0.75g,
0.0074 mol)
0.0074mol)
68
70
40-45
H2SO4 (98%) (20 ml) H2SO4 (98%) (20 ml)
NaNO3 (0.383g,
KNO3(0.455g,
0.0045 mol)
0.0045 mol)
63
66
H2SO4 (98%) (20 ml)
AgNO3 (1.257g,
0.0074 mol)
78
H2SO4 (98%) (20 ml)
AgNO3 (0.764g,
0.0045 mol)
70
2,6,8,12-Tetraacetyl 2,4,6,8,10,12-hexaazaisowurtzitane (TAIW)
(1g, 0.003 mol)
CL-20
2.5
45-50
H2SO4 (98%) (25 ml)
NaNO3 (1.913g,
0.0225 mol)
60
H2SO4 (98%) (25 ml)
KNO3 (2.274g,
0.0225 mol)
71
H2SO4 (98%) (20 ml)
AgNO3 (3.822g,
0.0225 mol)
75
4,6-dihydroxy-2methylpyrimidine
(1g, 0.0082 mol)
FOX-7
3
10-25
Imidazole
(0.5g, 0.0074 mol)
4-NI
4
45-50
H2SO4 (98%) (25 ml)
NaNO3 (1.743g,
0.0205 mol)
74
H2SO4 (98%) (20 ml)
NaNO3 (0.79g,
0.0093 mol)
49
H2SO4 (98%) (25 ml)
KNO3 (2.07g,
0.0205 mol)
75
H2SO4 (98%) (20 ml)
KNO3(0.935g,
0.0093 mol)
48
H2SO4 (98%) (20 ml)
AgNO3 (3.482g,
0.0205 mol)
80
H2SO4 (98%) (20 ml)
AgNO3 (1.58g,
0.0093 mol)
51
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SAIKIA et al.: SYNTHESIS OF SOME POTENTIAL HIGH ENERGY MATERIALS
Table 2—Chemical structure of synthesized compounds
N
O2 N
NH
N
NO2
H3C C CH2
O
NO2
H
3-Nitro-1,2,4-triazol-5-one (NTO)
O2N
NO2
NO2
N CH2
C CH3
O2N
N
N
N
N
NO2
NO2
H2 N
C
H2 N
C
NO2
O2 N
N
NO2
NO2
N
O2N N
Bis (2,2-dinitropropyl) nitramine
(BDNPN)
N NO
2
2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12hexaazaisowurtzitane (CL-20)
1,1-Diamino-2,2-dinitroethylene
(FOX-7)
H
4-Nitroimidazole (4-NI)
Table 3—Characterization data of synthesized compounds
IR (cm-1)
Product
1
H NMR ( ppm)
Chemical shift ( ppm)
DSC (C)
Elemental (%)
Solvent used
NTO
3196 (-NH), 1689 (–C=O),
1540 and 1336 ( –NO2 )
8.28, (bs, 2H, -NH<)
DMSO-D6
257 (Exo.)
C, 18.34 (18.47)* ; H, 1.58
(1.55) * ; N, 42.88 (43.08)*
CL-20
3040 and 2844 (-CH), 1614,
1556 and 1332 (-NO2) etc.
8.19 (s, 2 H, -CH<) & 8.35
(s, 4 H, -CH<)
(CD3)2CO
253 (Exo.)
C, 16.38 (16.45)* ; H, 1.41
(1.38)* ; N, 38.43 (38.36)*
4-NI
3448 and 3141 (-NH), 3010
13.1 (bs, 1H, -NH-) 8.3
(-CH), 1557 and 1496 (-NO2), (s, 1H, -CH=) &
1332 (C=N) etc.
7.7 (s, 1H, -CH=)
DMSO-D6
305 (Endo.)
C, 31.8 (31.87)* ; H, 2.62
(2.67)* ; N, 37.2 (37.16)*
BDNPN
2987 (-CH), 1580, 1554, and
1372 (-NO2) etc.
DMSO-D6
187 (Exo.)
C, 21.94 (22.09)*; H, 3.05
(3.09)* ; N, 25.86 (25.77)*
FOX-7
3420 and 3149 (-NH2), 1554, 8.9 (bs, 4H, -NH2)
1517 and 1354 (-NO2) etc.
DMSO-D6
234 (Exo.) and
278 (Exo.)
C, 16.27 (16.22)* ; H, 2.75
(2.72)* ; N, 37.79 (37.84)*
5.1 (s, 4H, -CH2-) & 3.32
(s, 6H, -CH3)
* Theoretical value
Results and discussions
The synthesized compounds (Table 2) were
characterized by spectroscopic and thermal
techniques. The characterization data of the
products are summarized in Table 3. The results
revealed from the experiments suggest that metal
nitrate/H2SO4 nitrating agent requires milder
reaction conditions as well as lesser reaction
time. The yield obtained by this method (Table 1
& Fig. 1)) is comparable with the conventional
method of preparation of the respective HEMs.
Among the three metal nitrates AgNO 3 was
found to be more efficient nitrating agent for
the synthesis of HEMs. From the experimental
results the reactivity of the three metal nitrates
towards the nitration is found to be in the order
AgNO3>KNO3>NaNO3. This nitration method
does not release any hazardous nitric oxides during
the nitration against to the case of concentrated
nitric/sulphuric acids mixture. Therefore, this
nitration method can be considered as ecofriendly
process. Further, this method does not require
stringent cooling condition in the preparation
of FOX-7.
Fig. 1—Percentage yield of synthesized HEMs against each metal
nitrates
Conclusion
The present study described the synthesis of
various HEMs e.g. CL-20, FOX-7, NTO, BDNPN
and nitroimidazole using metal nitrate/H2SO4 as a
nitrating agent under milder reaction conditions as
well as lesser reaction time. The synthesized
compounds have been characterized by NMR, IR as
well as thermal techniques. Since, this method of
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J SCI IND RES VOL 73 JULY 2014
nitration is not associated with the evaluation of
hazardous nitric oxides, hence this approach can be
considered as an attempt towards the environmental
benign process. From the results it can be concluded
that this method certainly an alternative method
of preparation of high energy materials (HEMs) in
place of the conventional nitric/sulphuric nitration
mixture. The efficacy of the three metal nitrates
towards nitration is found to be in the order
AgNO3>KNO3>NaNO3.
Acknowledgments
Dr. A. Subhananda Rao, Director, HEMRL, Pune,
India and colleague of Energetic Material Research
Division, HEMRL, Pune, India for continuous support
and encouragement.
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