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Explosive and thermic compositions or charges – Containing nitrated organic compound – Nitrated acyclic – alicyclic or heterocyclic amine

Reexamination Certificate

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C540S554000

Reexamination Certificate

active

06391130

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for making 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo [5.5.0.0.
5,9
.0
3,11
]-dodecane, also commonly known as 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, HNIW or CL-20, and in particular relates to a continuous process for making HNIW.
2. Description of the Related Art
HNIW is a polycyclic caged nitramine oxidizer having the following chemical structure:
For most existing weapons systems, the most critical ingredient in terms of propellant and explosive performance is the oxidizer. HNIW, with its substantial increase in performance output, presents significant opportunities in energy capabilities for propellant and explosive systems. It may be possible to replace existing weapons system energetic fillers with HNIW to increase shaped charge anti-armor penetration, increase missile payload velocity and standoff, increase underwater torpedo effectiveness and lethality, and improve gun propellant impetus.
In view of the potential plethora of applications for HNIW, it would be advantageous to develop a continuous process for making HNIW in high production capacities.
According to one known process for making HNIW, HNIW is synthesized via nitration of the precursor, tetraacetyldiformyl-hexaazaisowurtzitane (“TADF”), as shown below:
TADF can be synthesized according to the procedure described in U.S. Pat. No. 5,739,325 to Wardle, entitled “Hydrogenolysis of 2,4,6,8,10,12-hexabenzyl-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0
5,9
.0
3,11
]dodecane,” the complete disclosure of which is incorporated herein by reference. However, nitrolysis of TADF to form HNIW of acceptable purity has been found to require long reaction times, such as on the order of 2 to 3 hours. Attempts to increase the kinetics of the reaction and shorten reaction times have resulted in the formation of formyl-containing impurities. Thus, it would be extremely difficult to produce HNIW of acceptable purity via a continuous process which involves the nitrolysis of TADF to HNIW, since long residence times are required for the nitrolysis of the presursor, TADF, to HNIW.
A series of acyl group-containing hexaazaisowurtzitane derivatives is disclosed in EP 0 753 519 A1, the complete disclosure of which is incorporated herein by reference. Examples 20 and 22 of this European publication collectively disclose a process in which 2,6,8,12-tetraacetyl-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0
5,9
0
3,11
]-dodecane (also known as tetraacetylhexaazaisowurtzitane or “TADH”) is, in a stepwise manner, first nitrosated with sodium nitrate and then oxidized with 100% nitric acid to form a dinitro intermediate, dinitrotetraacetylhexaazaisowurtzitane. After distilling off the nitric acid, the dinitro intermediate is reacted with a mixed acid consisting of 50 vol. % nitric acid (100%) and 50 vol. % sulfuric acid (100%) to form HNIW. However, it is reported that the second stage of the reaction took 8 hours at 0° C. followed by 67 hours at room temperature to go to completion.
It would therefore be a significant advancement in the art to provide a reasonably rapid, continuous process for the formation of HNIW. In particular, it would be a noteworthy advance in the synthesis of HNIW to significantly shorten the nitrolysis of TADF or TADH to HNIW.
SUMMARY OF THE INVENTION
In accordance with the principles of this invention, the above-mentioned and other advances in the art are attained by the provision of a process in which TADF is replaced with 2,6,8,12-tetraacetyl-2,4,6,8,10,12-hexaazatetracyclo-[5.5.0.0
5,9
0
3,11
]-dodecane (“TADH”), and subjecting the TADH to nitrolysis in the presence of a mixed acid to form HNIW. The mixed acid comprises at least one nitronium ion source and at least one strong acid preferably nitric acid and sulfuric acid, respectively) capable of generating nitronium ions from said source. The nitrolysis reaction is shown below:
The volumetric ratio of nitronium ion source (e.g., HNO
3
) to strong acid (e.g., H
2
SO
4
) is preferably selected so that when reacted at a temperature of 85° C., a product having undergone at least 99% conversion to nitramine is rapidly formed, preferably in no more than 10 minutes. More particularly, the volumetric ratio of HNO
3
:H
2
SO
4
is preferably about 7:3.
As referred to herein, the purity of the HNIW product can be rated based on a “conversion to nitramine” standard. Conversion to nitramine means 100 multiplied by the ratio of the number of available substituted and unsubstituted nitrogen groups (of the analyzed nitramines) converted to nitramine groups (N—NO
2
) divided by the total number of substituted (N—R) and unsubstituted (N—H) nitrogen groups (of the analyzed nitramines) that are capable of being converted to nitramine groups. The conversion to nitramine is determined by NMR analysis as follows. Analysis of HNIW by NMR produces two peaks. The first of these peaks represents the protons at the 3, 5,9, and 11-positions of HNIW, whereas the second of these peaks represents the protons at the 1-position and 7-position of HNIW. Generally, the first peak is approximately twice the area of the second peak, since the first peak accounts for twice as many protons as the second peak. Other nitramine impurities produced during HNIW synthesis are present during NMR analysis and produce their own distinct peaks. Nitramine conversion is determined by taking the ratio of the area of the second HNIW peak (for the 1,7-positioned protons) to the greatest area of any peak produced by protons of a nitramine other than HNIW, i.e., a nitramine impurity. Thus, a conversion to nitramine of at least 99% HNIW means that the smaller HNIW peak area of the 1,7-position protons from NMR analysis is at least 99 times the area of the peak of greatest area produced by protons of a nitramine impurity (that is, a nitramine other than HNIW).
In accordance with a preferred embodiment of this invention, the process of converting TADH to HNIW by nitrolysis with the mixed acid is conducted in a continuous manner.
These and other objects, features, and advantages of the present invention will become apparent from the following detailed description of the invention when taken in conjunction with the accompanying Figure which illustrates, by way of example, the principles of this invention.
BRIEF DESCRIPTION OF THE FIGURE
The accompanying FIGURE is a schematic view of a flow diagram of a continuous process for the nitrolysis of TADH to HNIW in accordance with an embodiment of this invention.
DETAILED DESCRIPTION OF THE INVENTION
As mentioned above, Examples 20 and 22 of EP 0 753 519 A1 collectively disclose a process in which TADH is selected as a precursor and, after being nitrosated and thereafter nitrated, is reacted with a mixed acid consisting of 50 vol. % nitric acid (100%) and 50 vol. % sulfuric acid (100%). However, it is reported that the mixed acid took 67 hours at room temperature to drive the reaction to completion.
Intuitively, and as dictated by known chemistry principles, it would seem that the rate of reaction would be increased by increasing the sulfuric acid concentration of the mixed acid, since an increase in the sulfuric acid concentration generates a corresponding increase in nitronium ion activity. However, the present inventors discovered, to their surprise, that high concentrations of strong acids, such as sulfuric acid, decrease the rate of HNIW formation. High proportions of such strong acids result in impure HNIW containing acetyl substituents being quickly precipitated from the reaction mixture before completion of the nitrolysis of TADH to HNIW. Hence, subsequent nitrolysis of the precipitated, partly nitrated TADH is consequently slowed.
The present inventors found that the reaction rate for the nitrolysis of TADH to HNIW can advantageously be increased by nitrolysis of the TADH with a mixture comprising nitric acid and a strong acid, preferably sulfuric acid, at prescribed volumetric ratios. The optimum volumetric ratio of

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