GB2393957A - Synthesis of hexaazaisowurtzitane derivatives - Google Patents

Abstract

Tetraacetyldibenzylhexaazaisowurtzitane is made by reaction, in dimethylformamide medium, of hexabenzylhexaazaisowurtzitane with acetic anhydride, in the presence of hydrogen, a palladium-based catalyst and a bromine-containing cocatalyst chosen from bromoaromatic derivatives and hydrobromic acid. The wurtzitane derivative can be converted to hexanitrohexaazaisowurtzitane by nitrosation followed by nitration. The invention also includes the alpha polymorph form of hexanitrohexaazaisowurtzitane.

Description

SYNTHESIS OF HEXAAZAISOWURTZITANE DERIVATIVES

The present invention relates to a process for the synthesis of certain hexaazaisowurtzitane derivatives, particularly of tetraacetyldibenzylhexazaiso-

wurtzitane, to its conversion to hexanitrohexaazaisowurtzitane, and to a new polymorphous form of hexanitrohexaazaisowutzitane.

Hexanitrohexaazaisowutzitane, i.e. 2,4,6,8,1 0,1 2-hexanitro-

2,4,6,8,10,12-hexaazatetracyclo[5.5.0.05 9.03 it]dodecane, is an explosive or oxidising charge which can be employed in pyrotechnic compositions. It has been described in a number of publications over some years.

These publications variously describe the physical, chemical and detonation properties of this compound and/or various polymorphous forms, and its use in explosive compositions, propellants or powders for armaments. For example, F. Foltz describes the thermal stability of the epsilon polymoph in a polyurethane-ester) in Propellants, Explosives, Pyrotechnics 19, 63-69 (1994). In Propellants, Explosives, Pyrotechnics 19, 19-25 (1994), the same author describes the thermal stability of the four polymorphous forms called alpha, beta, gamma and epsilon.

However, information relating to the synthesis of hexanitrohexa-

azaisowutzitane is very rare, imprecise and insufficient for a person skilled in the art, even with his or her general knowledge, to be able to make it. While the

- - 2 author of the abovementioned publications sometimes mentions that the compound has been obtained from hexabenzylhexaazaisowurtzitane, there is no description of

how the process is effected.

The most precise information concerning the synthesis appears in Japanese Patent Application JO632 1962A relating to the synthesis of hexakis(ti-

methylsilylethylcarbamyl)hexaazaisowurtzitane from hexabenzylhexaazaiso-

wutzitane. It is mentioned there that it is possible to obtain hexanitrohexaazaiso-

wutzitane from this silylated intermediate compound by first of all reacting it with nitrous acid and then with nitric acid, but no example of such a reaction is given, and no details concerning the operating conditions (temperature, concentration of the acids, medium, and the like) are indicated.

At the Long Beach (California USA) congress organised by the American Defence Preparedness Association and held at the Queen Mary Hotel on 2729 October 1986, Arnold T. Nielsen disclosed the synthesis of 4,10dibenzyl-

2,6,8,1 2-tetraacetyl-2,4,6,8, 1 0,12-hexaazatetracyclo[5.5.0.05 9.03 I] dodecane, also called tetraacetyldibenzylhexaazaisowutzitane, by reaction at 60 C for 6h, of hexabenzylhexaazaisowurtzitane with acetic anhydride in the presence of hydrogen and of Pd/C as catalyst. The yield is not very high (25%).

The author indicated, furthermore, that he had studied many operating conditions for nitration of tetraacetyldibenzylhexaazaisowurtzitane with the aim of obtaining hexanitrohexaazaisowutzitane, but it had never been possible to obtain this compound. Despite this prejudice, we have now found that it is possible to obtain hexanitrohexaazaisowurtzitane in good yield from tetraacetyldibenzyl-

hexaazaisowurtzitane, and that it is possible to improve considerably the yield in the synthesis of tetraacetyldibenzylhexaazaisowurtzitane from hexabenzylhexa-

azaisowurtzitane. According to the present invention, there is provided a process for the synthesis of tetraacetyldibenzylhexaazaisowutzitane by reaction of

i - 3 hexabenzylhexaazaisowurtzitane with acetic anhydride in the presence of hydrogen and of a palladium-based catalyst, characterized in that the reaction is performed in dimethylfomamide medium and in the presence of a bromine-

containing cocatalyst which is a bromoaromatic derivative or hydrobromic acid.

The invention also includes such a process wherein the tetraacetyl-

dibenzylhexaazaisowurtzitane formed is converted to hexanitrohexaazaisowurtzi-

tane by nitrosation of the tetraacetyldibenzylhexaazaisowurtzitane followed by nitration. In the synthesis of tetraacetyldibenzylhexaazaisowurtzitane according to the invention, the yield is considerably improved, e.g. up to 80% instead of 25%, by employing in combination with the palladium-based catalyst and acetic anhydride, a specific solvent, dimethylformamide (DMF) and a brominecontaining cocatalyst chosen from the group consisting of bromoaromatic derivatives and hydrobromic acid, the use of which in hydrogenolysis reactions is not mentioned in the state of the art. By a "bromoaromatic derivative" we mean a derivative in which at least one bromide atom is bonded directly to an aromatic rmg. The bromine-containing cocatalyst is preferably a bromobenzene derivative. Mono-, di- and tribromobenzenes are particularly preferred, especially monobromobenzene. Comparative tests carried out with solvents other than DMF, or in the absence of cocatalyst, and/or in the presence of a cocatalyst other than those mentioned above, show that this choice of experimental parameters according to the invention is not arbitrary and that it alone provides the technical effect found and sought after.

Palladium hydroxide is preferably employed as the palladium-based catalyst, for example on carbon atoms as a support. Also preferably, the palladium content, expressed as weight of metal relative to the weight of hexabenzylhexa-

azaisowurtzitane, is between 0.05% and 0.2%, still better between 0.1% and 0.2%.

i Higher palladium contents, for example 0.3% or 0.5%, can be employed without consequential influence on the reaction yield, but this is uneconomic.

The acetic anLydride is preferably employed in molar excess in relation to the hexabenzylhexaazaisowurtzitane. Furthermore, the molar ratio of the bromine-containing cocatalyst to hexabenzylhexaazaisowurtzitane is preferably between 0.015 and 0.5, still better between 0.025 and 0.25, and even better still between 0.03 and 0.10. It has been found, unexpectedly, that in these latter conditions, the greatest gain in yield is obtained and that the gain decreases as this ratio increases.

The duration of the reaction is generally a few hours, especially depending upon the temperature and the hydrogen pressure.

With regard to the temperature, it is preferred to begin the reaction at a temperature close to ambient temperature, for example between 0 C and 30 C, better still between 15 C and 25 C, and then to raise the temperature up to a temperature of between 45 C and 75 C, better still between 50 C and 60 C, and then to maintain this temperature.

The hydrogen must be well dispersed in the mixture, and it is consequently preferable to employ a fine dispersion system and an effective stirring system. The hydrogen pressure may, for example, be between 105 Pa and 5x105 Pa (I to 5 bar). A pressure of between 105 Pa and 2x105 Pa, or even between 105Pa and 1.5x105 Pa is perfectly suitable.

After the reaction, in order to recover the tetraacetyldibenzylhexa-

azaisowurtzitane formed, the latter may be, for example, completely dissolved in the reaction mixture by adding acetic acid to the mixture and heating, and then filtering to separate the catalyst from the filtrate. The required product is subsequently recovered conventionally by concentration of the filtrate.

In the synthesis of hexanitrohexaazaisowurtzitane according to the invention, the tetraacetyldibenzylhexaazaisowurtzitane obtained according to the invention is subjected to nitrosation using any suitable nitrosing agent, and then to

nitration using any suitable nitrating agent. The nitrosing agents and the nitrating agents are well known to a person skilled in the aft. For example, nitrogen tetroxide and nitrosonium salts are suitable nitrosing agents, and nitric acid, N2Os' sulphonitric or acetonitric mixtures and nitronium salts are suitable nitrating agents. The tetraacetyldibenzylhexaazaisowurtzitane is preferably reacted first of all with nitrogen tetroxide. In this case nitrogen tetroxide, a nitrosing agent, can also act as a solvent.

In general, the nitrosation and/or nitration reactions clan be performed in an organic solvent medium, preferably a chlorine-containing solvent such as chloroform, 1,2-dichloroethane and methylene chloride, which is particularly preferred. When the nitration is performed with concentrated nitric aid or with a sulphonitric mixture, it suffices, for example, after the nitrosation step, to add concentrated nitric acid or the sulphonitric mixture to the reaction mixture.

The nitrosation temperature is preferably between 10 C and 35 C, for example ambient temperature, and the nitration temperature is preferably between 45 C and 85 C. The nitrosing and nitrating agents are preferably employed in excess in relation to tetraacetyldibenzylhexaazaisowurtzitane.

After isolation of the desired product by conventional methods it was found, unexpectedly, especially by X-ray and Fourier transform infrared analyses that the hexanitrohexaazaisowurtzitane thus obtained was in the alpha form as described in the state of the art, especially by Foltz in the abovementioned papers.

The present invention thus includes the alpha polymorph form of hexanitrohexaazaisowurtzitane, the synthesis of which was not known to a person skilled in the art, nor suggested by the state of the art.

In order that the present invention can be more fully understood, the following Examples are given by way of illustration only. Examples 4, 12 and 18 to 21 are not according to the invention.

i - 6 Examples I to 24: Synthesis of tetraacetyldibenzylhexaazaisowurtzitane Example 1

Into a 250-ml jacketed reactor fitted with magnetic stirring, a water condenser and an entry tube equipped with a sinter for the introduction of

hydrogen, there are introduced at ambient temperature (15-20 C), 67ml of DMF, 17ml of acetic anhydride, 0.23g (1.46 Drool) of bromobenzene, 20.8g (29.4 mmol) of hexabenzylhexaazaisowutzitane and I.15g of palladium hydroxide on carbon (moisture: 50%, palladium content in the dry substance: 5%).

After purging the apparatus with an inert gas, and while introducing hydrogen into the mixture and maintaining its pressure in the reactor between 1.13 105 Pa and 1.25 105 Pa, the reaction mixture is heated from ambient temperature to 55 C over 3 hours and this temperature is then maintained for 2 hours.

The introduction of hydrogen is then stopped and 158ml of acetic

acid are introduced into the mixture, which is then heated to a temperature of between 80 C and 90 C. The mixture is then filtered in order to separate off the catalyst, and the filtrate is concentrated at 60 C-70 C under a reduced pressure of 2.5x103 Pa to 5x103 Pa (approximately 20mm to 40mm Hg).

After return to ambient temperature, the residue is taken up with lOOml of acetone. The tetraacetyldibenzylhexaazaisowurtzitane obtained, which has precipitated, is filtered off and rinsed with 50ml of acetone. After drying for 24h at 30 C under a reduced pressure of 5x103 Pa (approximately 40mm Hg), 12. lg (80% yield) tetraacetyldibenzylhexaazaisowurtzitane are obtained. The product is identified by mass spectrometry, infrared and 60 MHz proton NMR reference spectra.

Examples 2 and 3: Influence of the hydrogen pressure In these two Examples, the procedure of Example I was repeated precisely except that the hydrogen pressure is 2x105 Pa (2 bar) in the case of Example 2, and 3. 6x105 Pa (3.6 bar) in the case of Example 3.

- 7 The yield of tetraacetyldibenzylhexaazaisowurtzitane isolated is 81. 4% in the case of Example 2 and 75% in the case of Example 3.

Examples 4 to I 1: Influence of the quantity of bromobenzene In these Examples, the procedure of Example 1 was repeated precisely but with different quantities of bromobenzene to hexabenzylhexaazaisowurtzitane were, in the case of these Examples 4 to 11, 0 (no bromobenzene), 0.03, 0. 10, 0.18, 0.33, 0.5, 0.7 and 1, respectively.

The yields of tetraacetyldibenzylhexaazaisowurtzitane isolated are 15%, 79%, 79%, 77%, 73%, 70%, 50% and 45% respectively.

Examples 12 to 16: Influence of the quantity of Pd(OH)2/C catalyst In these Examples, Example 1 was repeated reproduced but with different quantities of Pd(OH)2/C catalyst, namely O (no catalyst), 0.41g, 0.83g, 2. 1g and 4.2g, respectively, in the case of these Examples 12 to 16, instead of 1.15g in the case of Example 1.

The yields of tetraacetyldibenzylhexaazaisowurtzitane isolated are 0%, 45%, 82%, 80% and 78% respectively.

Example 17: Influence of the temperature rise In this Example, Example 1 was repeated but the conditions of temperature rise of the reaction mixture were modified.

The reaction mixture is first of all heated from ambient temperature to 60 C over 2h, the temperature is lowered to 40 C over 0.5h and the temperature is then raised to 55 C over 0.5h. This temperature is then maintained for 2h.

The yield of tetraacetyldibenzylhexaazaisowurtzitane isolated is 83.5%.

Examples 18 to 21: Influence of the nature of the solvent In the case of these four Examples, the procedure of Example I was reproduced precisely but using, instead of DMF, chloroform in the case of Example 18, 1,2dichloroethane in the case of Example 19, a 50/50 DMF/chloroform mixture by volume in the case of Example 20 and a 50/50

- 8 DMF/1,2-dichloroethane mixture by volume in the case of Example 21.

In the case of all these Examples 18 to 21, the yield of desired product is zero.

Examples 22 to 23: Influence of the nature of the cocatalyst In these two Examples, the procedure of Example 1 was reproduced precisely but using, instead of bromobenzene, the same molar quantity of hydrobromic acid in the case of Example 22 and of N-bromosuccinimide in the case of Example 23.

The yield is 81% in the case of Example 22 and zero in the case of Example 23.

Example 24: Synthesis of hexanitrohexaazaisowutzitane by nitrosation with a nitrosonium salt and then nitration with a nitronium salt 63g of sulpholane, 0.28g of water and 6.3g (5.4x 10-2 mol) of nitrosonium fluoroborate are introduced into a 150-ml reactor. After 0.5h of stirring at ambient temperature lg (2xlO mol) of tetraacetyldibenzylhexa-

azaisowurtzitane obtained according to Example 1 is introduced.

The mixture is stirred Ih between 17 C and 20 C, heated gradually over 0. 7h to 55 C and this temperature is then maintained for lh. The mixture is then cooled to 17 C and then 5.16g (3.8x10 2 mol) of nitronium fluoroborate are added. The temperature is gradually raised to 55 C over Ih and this temperature is then maintained for lh. The mixture is then cooled to 17 C and 50ml of water are then added dropwise while the temperature is kept lower than 20 C. The reaction mixture is poured into a 10ml beaker and 51 of water are then introduced gradually and with stirring. After standing for 12h at 5 C, the precipitate fomed is isolated by filtration and is then dried under reduced pressure in the presence of phosphorus pentoxide. Hexanitrohexaazaisowurtzitane 0.73g (86% yield) is obtained, a white solid identified by 200 MHz proton NMR in dimethyl sulphoxide (DMSO), by carbon NMR in the same conditions, by IR, by elemental analysis and by X-ray crystallography study. Its melting temperature is close to 170 C and its

purity can be estimated as higher than 95%. Its density is 1.95g/cm3, determined by the gas pycnometer method and 1.97g/cm3 according to the crystallographic data obtained using X-rays.

The crystallographic study of a single crystal using X-rays shows that this compound crystallizes with approximately 25 mol% of water and that it has an orthorhombic crystal structure of Pbca space group which has the following lattice constants: a = 9.546A, b = 13.232A, c = 23.634A and Z=8.

Furthermore, the Fourier transform IR spectrum of a 1% dispersion in KBr exhibits, between 700 cm' and 1200 cm. the characteristic peaks of the alpha polymorph foam, with reference to the abovementioned Foltz publication, Table 1 page 66. The characteristic peaks of the epsilon, beta and gamma forms are not observed.

The hexanitrohexaazaisowurtzitane obtained is therefore in the alpha polymorph form.

Example 25: Synthesis of hexanitrohexaazaisowurtzitane by nitrosation with nitrogen tetroxide and then nitration with concentrated nitric acid Liquid N2O 313g (3.37 mol) is introduced into a jacketed one-litre reactor equipped with mechanical stirring and a temperature probe. Tetraacetyl-

dibenzylhexaazaisowurtzitane 133g (0.259 mol) obtained according to Example 1, is added between 0 C and 5 C. The temperature of the reaction mixture is allowed to rise to 15-16 C (N2O, reflex) and the mixture is then left with stirring and under N2O reflux for 20h.

After the mixture has been cooled to 0 C, 667ml of a sulphonitric mixture, 20/80 by volume respectively, are added between 0 C and 8 C, which corresponds to the addition of 12.8 mol of nitric acid. The mixture is then heated gradually so as to remove the excess N2O, by distillation and then, when the temperature of the mixture reaches 73-75 C, the mixture is left with stirring for 4h.

After cooling to 40 C, the mixture is poured onto 21 of a mixture of water and ice. A solid separates out, which is recovered by filtration and washing

- 10 with warm water (40 C) on the filter until the pH of the aqueous washes is neutral.

After drying, 1 04g (97% yield) are obtained of hexanitrohexa-

zaisowurtzitane, which is identified as in Example 25. The purity is estimated as higher than 95% according to the analyses performed. It exhibits the same crystal structure as the product obtained according to Example 25, that is to say in particular that it is in the alpha polymorph form.

Claims (12)

- 11 CLAIMS:

1. A process for the synthesis of tetraacetyldibenzylhexaazaiso-

wurtzitane by reaction of hexabenzylhexaazaisowurtzitane with acetic antydride in the presence of hydrogen and of a palladium-based catalyst, characterised in that the reaction is performed in dimethylformamide medium and in the presence of a bromine-containing cocatalyst which is a bromoaromatic derivative or hydrobromic acid.

2. A process according to Claim 1, wherein the palladium-based

catalyst is palladium hydroxide.

3. A process according to Claim 2, wherein the palladium content is between 0.1% and 0.2% by weight relative to the hexabenzylhexaazaisowurtzitane.

4. A process according to Claim 1, 2 or 3, wherein the bromine-

containing cocatalyst is a bromobenzene derivative.

5. A process according to Claim 1, 2, 3 or 4, wherein the molar ratio of the bromine-containing cocatalyst to hexabenzylhexaazaisowurtzitane is between 0.03 and 0.1.

6. A process according to any of Claims I to 5, wherein the temperature of the reaction mixture is raised from between 0 C and 30 C to a temperature between 45 C and 75 C at which it is then maintained.

7. A process according to any of Claims I to 6, wherein after the reaction of hexabenzylhexaazaisowurtzitane with acetic antydride, the tetraacetyldibenzylhexaazaisowutzitane formed is recovered by heating the

- 12 mixture after addition of acetic acid, and then by filtration of the mixture and concentration of the filtrate.

8. A process according to any of Claims I to 7, wherein the tetraacetyl-

dibenzylhexaazaisowurtzitane formed is converted to hexanitrohexaazaiso-

wutzitane by nitrosation of the tetraacetyldibenzylhexaazaisowutzitane followed by nitration.

9. A process for the synthesis of tetraacetyldibenzylhexaazaisowutzi-

tane substantially as herein described in any of Examples I to 3, 5 to I I and 13 to 16.

10. A process for the synthesis of hexanitrohexaazaisowurtzitane substantially as herein described in Example 24 or 25.

Alpha polymorph form of hexanitrohexaazaisowuitzitane.

12. A pyrotechnic composition which comprises hexanitrohexaazaiso-

wurtzitane made by the process of claim 7 or 9, or as claimed in claim 10 or 11.

12. Alpha polymorph form of hexanitrohexaazaisowutzitane substantially as herein described in Example 24 or 25.

13. A pyrotechnic composition which comprises hexanitrohexaazaiso-

wurtzitane made by the process of claim 8 or 10, or as claimed in claim I I or 12.

A'nendmcuts to the claims have been filed as follows 1. A process for the synthesis and recovery of tetraacetyldibenzyl-

hexaazaisowurtzitane by reaction of hexabenzylhexaazaisowurtzitane with acetic anhydride in the presence of hydrogen and of a palladium-based catalyst, characterised in that the reaction is performed in dimethylformamide medium and in the presence of a bromine-containing cocatalyst which is a bromoaromatic derivative or hydrobromic acid, and in that the tetraacetyldibenzylhexaazaiso-wurtzitane so formed is recovered by heating the mixture after addition of acetic acid, followed by filtration of the mixture and concentration of the filtrate.

2. A process according to Claim 1, wherein the palladium-based catalyst is palladium hydroxide.

3. A process according to Claim 2, wherein the palladium content is between 0.1% and 0.2% by weight relative to the hexabenzylhexaazaiso-

wurtzitane. 4. A process according to Claim 1, 2 or 3, wherein the bromine-

containing cocatalyst is a bromobenzene derivative.

5. A process according to Claim 1, 2, 3 or 4, wherein the molar ratio of the bromine-containing cocatalyst to hexabenzylhexaazaisowurtzitane is between 0.03 and 0.1.

6. A process according to any of Claims 1 to 5, wherein the temperature of the reaction mixture is raised from between 0 C and 30 C to a temperature between 45 C and 75 C at which it is then maintained.

lid 7. A process according to any of Claims 1 to 6, wherein the tetraacetyl-

dibenzylhexaazaisowurtzitane formed is converted to hexanitrohexaazaiso-

wurtzitane by nitrosation of the tetraacetyldibenzylhexaazaisowurtzitane followed by nitration.

8. A process for the synthesis of tetraacetyldibenzylhexaazaisowurtzi-

tane substantially as herein described in any of Examples 1 to 3, 5 to 1 1 and 13 to 16. 9. A process for the synthesis of hexanitrohexaazaisowurtzitane substantially as herein described in Example 24 or 25.

10. Alpha polymorph form of hexanitrohexaazaisowurtzitane.

11. Alpha polymorph form of hexanitrohexaazaisowurtzitane substantially as herein described in Example 24 or 25.