METHOD FOR PRODUCING THE PENTAZOLATE ANION USING A HYPERVALENT IODINE OXIDANT

Abstract

A method for producing the pentazolate anion, includes at least the oxidation of a phenolic arylpentazole by a particular hypervalent iodine oxidant in the presence of a base.

Claims

1. A method for producing the pentazolate anion, comprising: oxidation of a phenolic arylpentazole by a hypervalent iodine oxidant in the presence of a base, said hypervalent iodine oxidant being of general formula A-B, wherein group A designates a benzene ring, and group B is a structure comprising a hypervalent iodine atom having one of the two formulas B1 or B2 below: ##STR00011## with * designating, in the formulas B1 and B2, the bond of the hypervalent iodine atom to the benzene ring A, in formula B2, R.sub.1 and R.sub.2 being identical or different and chosen independently of one another from: **OCOR, **OR, where R designates a linear or branched, alkyl chain comprising between 1 and 4 carbon atoms, or R.sub.1 being **OH and R.sub.2 being **OTs with Ts designating a tosyl group, where ** designates the bond of the oxygen atom to the hypervalent iodine, the phenolic arylpentazole having the following chemical structure: ##STR00012## R.sub.3 and R.sub.4 being identical or different and chosen independently of one another from: the, linear or branched, alkyl chains comprising between 1 and 4 carbon atoms, not substituted or substituted by a C.sub.1 or C.sub.2 alkoxy group or by a dialkylamine.

2. The method according to claim 1, wherein the oxidation is carried out in a solvent comprising hexafluoroisopropanol and at least one compound chosen from alcohols or acetonitrile.

3. The method according to claim 1, wherein group B is of formula B1.

4. The method according to claim 3, wherein group B is of formula B1 and the oxidation is carried out in a solvent comprising hexafluoroisopropanol and at least one compound chosen from alcohols or acetonitrile.

5. The method according to claim 1, wherein group B is of formula B2 with R.sub.1 and R.sub.2 identical and each designating **OCOMe or **OMe, where Me designates a methyl group.

6. The method according to claim 1, wherein the base comprises at least one compound chosen from: an alkali hydroxide, an alkaline-earth hydroxide, a metal hydroxide, ammonium hydroxide, a quaternary ammonium hydroxide, an alkali carbonate or a mixture of these compounds.

7. The method according to claim 6, wherein the base is sodium hydroxide.

8. The method according to claim 1, wherein the oxidation is carried out in a solvent and wherein the method further comprises, successively: removal of the solvent, liquid-liquid extraction, using an extraction solvent, in order to remove the oxidant residues, removal of the extraction solvent, and selective extraction of the pentazolate anion after this removal, the pentazolate anion being selectively extracted in a liquid medium comprising at least one of ethanol, acetonitrile or acetone, or a mixture of these compounds.

9. A method for producing an energetic composition, comprising at least the production of the pentazolate anion by a method according to claim 1, and mixing of the pentazolate anion thus produced with a binder in order to obtain the energetic composition.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0048] FIG. 1 is a result from an analysis by ionic chromatography, carried out after implementing an example of the method according to the invention, this figure highlights the presence of the pentazolate anion.

[0049] FIG. 2 is a result from an analysis by .sup.14N NMR, with external calibration with NH.sub.4Cl, carried out after implementing an example of the method according to the invention.

[0050] FIG. 3 is a result from an analysis by differential scanning calorimetry, carried out after implementing an example of the method according to the invention.

EXAMPLES

Preparation of the arylpentazole precursor (catalytic reduction of 2,6-dimethyl-4-nitrophenol)

[0051] In a 1-L three-necked flask, palladium on carbon (Pd/C, 10% by mass, 240 mg) is placed in suspension in 44 mL of distilled water, the system is then swept with argon. A solution of sodium borohydride (NaBH.sub.4) (4.54 g, 120 mmol) in 100 ml of a solution of sodium hydroxide (NaOH) 0.1 N is added dropwise (for approximately 20 minutes) at ambient temperature (20 C.). A solution formed of 2,6-dimethyl-4-nitrophenol (10.00 g, 60 mmol) in 360 mL of an aqueous solution of NaOH 1N (solution heated to 40 C. to facilitate the solubilisation) is then added dropwise (for approximately 60 minutes). The reaction medium is stirred at ambient temperature for 4 hours then filtered over celite (washing with water). An aqueous solution of hydrochloric acid (HCl) 3N (400 mL) is added to the filtrate, then the latter is washed with 3*100 mL ethyl acetate (EtOAc). The aqueous phase is concentrated (80 mL), then 100 mL of a 37% HCl solution are added. The solution is placed in the refrigerator overnight, then the precipitate is filtered. This precipitate is dissolved in 200 ml of distilled water, then this solution is neutralised by addition of sodium hydrogencarbonate (NaHCO.sub.3) to a pH7/8. The aqueous phase is extracted by 3*100 mL of EtOAc, then the combined organic phases are dried on magnesium sulfate (MgSO.sub.4), filtered and evaporated until dry. The product is obtained in the form of a violet solid corresponding to 3,5-dimethyl-4-hydroxyaniline (7.35 g, 91%).

Preparation of the Arylpentazole Precursor (Diazotation then Aziding)

[0052] In a 250-mL three-necked flask, 3,5-dimethyl-4-hydroxyaniline (3.00 g, 22 mmol, Eq. 1) is dissolved in 17 mL of tetrahydrofurane (THF), then the solution is cooled to 5 C. A solution of 37% HCl (3.25 mL, 40 mmol, 1.8 eq.) is then added dropwise while controlling the heat release. A solution of sodium nitrite (NaNO.sub.2) (1.59 g, 23 mmol, 1.05 eq.) in 8 mL of a MeOH/H.sub.2O (1/1 v/v) mixture is then added dropwise while maintaining the temperature of the reaction medium below 2 C. After the end of the addition, the reaction medium is stirred at 5 C. for 30 minutes then cooled to 40 C. Then 75 mL of a MeOH/heptane (1/2 v/v) mixture, cooled beforehand to 40 C., is added in one go, then the stirring is increased in order to create an emulsion. A solution, cooled beforehand to 40 C., of sodium nitride (NaN.sub.3) (1.50 g, 23 mmol, 1 eq.) in 8 mL of a MeOH/H.sub.2O (1/3 v/v) mixture is then added dropwise. After 15 minutes stirring at 40 C., the solution is filtered over a double-envelope frit maintained at 40 C. The phenolic arylpentazole product is obtained in the form of a violet solid and stored in a plastic bottle at 196 C. An analysis by 1H NMR (400 MHZ, CD.sub.3OD) generally shows a ratio of ArN.sub.5/ArN.sub.3 of approximately 9/1.

Oxidation for the Generation of the Pentazolate Anion

[0053] 30 mL of hexafluoroisopropanol (HFIP) are added to a solution of NaOH (0.44 g, 11 mmol) in 30 mL of MeOH, then this mixture is cooled to 40 C. The phenolic arylpentazole precursor, stored at 40 C., is then added in one go. The oxidant iodosylbenzene (PhIO) (2.42 g) is added in portions, then the reaction medium is stirred for 24 hours at 40 C., then left to rise slowly to ambient temperature (20 C.). The solvents are evaporated until dry, then the residue is recovered with 100 ml of an H.sub.2O/EtOAc (1/1 v/v) mixture. The aqueous phase is washed with 3*20 mL EtOAc then evaporated till dry (co-evaporation with ethanol). The solid thus obtained is analysed by high-resolution mass spectrometry (HRMS), chemical ionisation (CI) and .sup.14N NMR in order to confirm the presence of the pentazolate anion. The average mass content observed is approximately 5-10% nitrogen and the major contaminant is NaCl.

[0054] The reaction diagram below summarises the method for synthesising the pentazolate anion implemented in this example.

##STR00008##

Purification of the Pentazolate Anion

[0055] The solid obtained previously after the oxidation (1 g) is placed in suspension in 100 ml of an anhydrous solvent (acetonitrile or acetone). After stirring for 3 days, the solid is filtered, washed with small volumes of solvent, then the solvent is evaporated until dry. Between 50 and 80 mg of a yellowish solid is recovered. The analysis by .sup.14N NMR is used to determine a mass content of approximately 40 to 45% of pentazolate anion.

[0056] FIGS. 1 to 3 give the physicochemical characteristics of the resulting product and show the detection of the pentazolate anion. FIG. 1 is a result from an analysis by ionic chromatography. FIG. 2 is a result from an analysis by .sup.14N NMR showing a characteristic chemical shift ( 367 ppm vs. NH.sub.3, standard NH.sub.4Cl at 20 ppm). FIG. 3 is a result from an analysis by differential scanning calorimetry (DSC) showing a decomposition temperature of approximately 110 C. in accordance with that described in the literature for NaN.sub.5.Math.xH.sub.2O complexes with x between 2 and 3.

[0057] Other tests were carried out by varying the nature of the oxidant and of the solvent during the oxidation of phenolic arylpentazole and are listed in Table 1 below (the test denoted Exp. 3 in the table below corresponds to the operating mode which will be described below). An operating mode identical to that described above was used for these tests replacing, as applicable, HFIP by CH.sub.3CN or TFE, and PhIO by PIDA.

TABLE-US-00001 TABLE 1 Exp. Oxidant Solvent Base Gross m (g) Mass N (%) N5 (mmol) Yield (%) 1 PIDA MeOHCH.sub.3CN NaOH 0.32 2.8 0.13 19.5 2 PhIO MeOHTFE NaOH 1.74 1.3 0.32 8.7 3 PhIO MeOHHFIP NaOH 1.76 7.8 1.93 52.5 4 PIDA MeOHTFE NaOH 1.68 2.7 0.64 17.4 5 PIDA MeOHHFIP NaOH 1.06 6.1 0.93 25.2 6 PhIO MeOHHFIP 0.45 2.7 0.17 4.8 7 PhIO MeOHHFIP NaOH 1.73 6.3 1.55 34.8

[0058] Table 1 shows the effectiveness of the oxidants PhIO and PIDA in various solvents for obtaining the pentazolate anion. It can be seen that the removal of the base (Exp. 6) prevents the formation of the N.sub.5.sup. species and that the use of PhIO in an MeOHHFIP solvent in the presence of NaOH gives an optimum result (Exp. 3) which is reproducible (Exp. 7).

[0059] Another series of tests was carried out using other oxidants and bases. The results are listed in Table 2 below. In this series of tests, the operating mode for oxidation is identical to that described above by replacing PhIO by PhI(OMe).sub.2 or IBX, HFIP by CH.sub.3CN or TFE and NaOH by MeONa, as applicable.

TABLE-US-00002 TABLE 2 Exp. Oxidant Solvent Base Gross m (g) Mass N (%) N5 (mmol) Yield (%) 8 PhI(OMe).sub.2 MeOHCH.sub.3CN NaOH 2.39 1.1 0.39 10.5 9 PhI(OMe).sub.2 MeOHTFE NaOH 1.07 2.6 0.40 11.1 10 PhI(OMe).sub.2 MeOHHFIP NaOH 1.65 3.4 0.80 21.9 11 PhI(OMe).sub.2 MeOHTFE MeONa 1.16 6.2 1.02 27.9 12 IBX MeOHCH.sub.3CN NaOH

[0060] Table 2 shows the effectiveness of the oxidant PhI(OMe).sub.2 in various solvents in order to generate the pentazolate anion. The possibility of using an alcoholate base (Exp. 11) should also be noted and the total ineffectiveness of IBX (Exp. 12) of the formula given below, an oxidant not within the scope of the invention of type I(V) (whereas the oxidants PIDA, PhIO and PhI(OMe).sub.2 are of type I(III)).

##STR00009##

[0061] An oxidation test of phenolic arylpentazole using Koser's reagent of formula given below was also carried out using an ammonium hydroxide base and led to a yield of 25% for the oxidation step.

##STR00010##

[0062] The expression between . . . and . . . should be understood as including the limits.