186 Letters in Organic Chemistry, 2011, Vol. 8, No. 3
Qian et al.
proved by the formation of some low melting compounds.
Their IR spectrum indicates the cleavage of the cage
structure which could be an explanation for decreased yields
with high-frequency ultrasound.
irradiation in IL as solvent. Various operating parameters
such as temperature, volume of solvent and molar ratio of
reagents have been optimized to give maximum yield of the
desired product. This reaction has a wide scope in the
nitrolysis of a variety of other nitrogen heterocycles.
Moreover, sonochemistry in IL as described in the present
work has opened up a new domain in the area of
sonochemistry and liquid interface science and can be
conceptually envisaged as a new tool in organic synthesis.
Further work is in progress to extrapolate these findings to
other organic transformations.
Effect of Solvent
As shown in entries 2-4, IL can effectively promote this
reaction. As we know, solvent with lower vapor pressure is
in favor to enhance the efficiency of ultrasound [14-16, 19].
That’s why ionic liquid can highly promote this reaction.
Furthermore, the nitrolysis reaction studied here is a
+
bimolecular electrophilic substitution in which NO2 attacks
ACKNOWLEDGEMENTS
the lone pair on the nitrogen atom and the cleavage of the C-
N bond and the formation of the new N-N bond occurs at the
same time. The dependence of the reaction yield on the
concentration of N2O5 seems to support the idea that the
elementary reaction of the nitrolysis is bimolecular. Since
the electrophilic reaction involves ionic reaction
intermediates, another role of ionic liquid to enhance the
reaction yield would be the stabilization of these
intermediates. From entries 4 and 7-8, it can be seen that
there was a higher yield when lower amount of solvent was
used.
This work has been supported by the 8th Explosive &
Propellants Funding of the General Reserve Department
(hzy08020305-5). We also thank Science Development Fund
of Nanjing University of Science and Technology
(2010GJPY008 and 2010ZYTS020) for financial assistance.
The part of information included in this article has been
previously published in Ultrasonics Sonochemistry Volume
15, Issue 4, April 2008, Pages 326-329.
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With increasing reaction volume the power dissipated per
unit volume i.e. power density in the reaction mixture
decreases and this also decreases the number of cavitational
events per unit time per unit volume. From these initial
studies it was decided to use a minimum possible solvent
volume (10 ml IL) for further reactions.
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Effect of Molar Ratio of HNO3, N2O5 and DPT
In the experiments we fixed the molar number of DPT
and NH4NO3, then changed the amount of N2O5 and HNO3 to
find the influences on the yield. As the results shown in
entries 4 and 11-14, there was a significant effect on the
yield when changing the molar ratio of N2O5. Slightly higher
N2O5 concentrations with respect to DPT increased the yield
rapidly as the amount of N2O5 grew but higher N2O5/DPT
ratios than 3 led to a lower yield. LC/MS analysis of
nitrating systems with high N2O5 concentration confirmed
the cleaved ring structure. Compared with N2O5, the
concentration of HNO3 was less important for the yield.
Indeed little increase of HNO3 induced a higher yield but too
much nitric acid reduces the yield of HMX for the dilution of
N2O5.
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CONCLUSION
A new process to synthesize HMX from DPT with
relatively high yield has been developed using ultrasonic