Process for producing 5,5–azo and -hydrazo derivatives of explosive tetrazoles

Abstract

The invention describes a process for producing soluble salts of 5,5-azotetrazole (5,5-AT) by oxidation of 5-aminotetrazole with a soluble peroxodisulfate in a strongly alkaline environment. This compound is a precursor of the energetic component of non-toxic priming mixtures, 5,5- bis-hydrazino-tetrazole (BTH). BTH can be prepared by reduction of salts or solutions of 5,5-AT with ascorbic acid. 5,5-AT

Description

DescriptionTitle of Invention: Process for producing 5,5-azo and -hydrazo derivatives of explosive tetrazoles Technical Field

[0001] The invention relates to the production of ammunition, gas generators and rocket fuel.Background Art

[0002] Energetic compounds based on five-membered nitrogenous heterocycles - tetrazoles- have been known since the end of the 19th century. These compounds, which were already described by the German chemist J. Thiele, are today - after more than 100 years - experiencing their boom and mainly thanks to German chemists - dr. Klapotke - hundreds more of these compounds have been described within last 20 years! Unfortunately, an overwhelming majority of these compounds are of scientific significance only and they can only be prepared on the laboratory scale.

[0003] The Sellier & Bellot company, one of the largest current European manufacturers of small-arms ammunition and primers, had also recognized the potential of these compounds in time and chose the approach of using salts and derivatives of tetrazoles. However, explosives for the primers of ammunition are subject to very specific requirement - capability of stable burning without the risk of transition into an explosion and a minimal dependence of the burning rate on pressure, the highest flame temperature as possible and the contents of solids or liquids in the combustion products- for an optimum transfer of heat from the priming mixture to the powder, wherein the by far most efficient mechanism of said heat transfer is associated with a phase change- e.g. condensation of vapors of a low-boiling metal. Therefore, the most successful explosives in the development history of firearms, and mainly since the beginning of the 19th century, when the percussion lock was invented, have been salts of heavy, noble metals (mercury fulminate and lead styphnate) but unfortunately, both these compounds are highly toxic. None of the later replacements of these explosive salts with compounds having no metal content (e.g. diazodinitrophenol or tetrazene) has had a comparable ignition power and sufficient burning stability (unavailability for rimfire or larger-arms ammunition).

[0004] Therefore, Sellier & Bellot have opted for a unique solution - to combine the huge explosive potential of nitrogen-containing heterocycles with a heavy, noble, low- boiling, but non-toxic metal - Bi. After many years’ intensive research, the basic Bi salt of 5,5- azotetrazole has proved to be an optimum compound as the main explosive for a new, non-toxic priming mixture, and 5,5-bis-hydrazinotetrazole as thesecond, highly energetic ingredient. A precursor for both these compounds is a soluble inorganic salt (e.g. disodium salt) or organic salt (guanidinium salt) of 5,5-azotetrazole, wherein in the former case, simple precipitation with soluble salts of Bi, in the latter case, an oxidation-reduction reaction is employed.

[0005] The above-mentioned compound, e.g. the disodium salt of 5,5-bis-azotetrazole (hereinafter ATNa2) pentahydrate and 5,5-bis-hydrazinotetrazole (hereinafter BTH) can be prepared on the laboratory scale with the use of methods that were already mentioned by Thiele and nothing has changed in the art since. These methods, based on oxidative dimerization of 5-aminotetrazole in the former case and on simple reduction of thus obtained ATNa2pentahydrate resulting in BTH in the latter case, are not very complicated on the laboratory scale, either in terms of usable laboratory equipment, or in terms of using special or unavailable chemicals or work safety. However, attempts to implement these processes to pilot-plant or mass production encounter serious technological problems.

[0006] For the laboratory preparation of ATNa2pentahydrate, Thiele proposed a seemingly simple method, based on oxidative dimerization of 5-aminotetrazole, which is currently the most widespread and fully available non-explosive tetrazole derivative, with solid potassium permanganate in a strongly alkaline solution under hot conditions. An equation that only very approximately describes this reaction can be found, e.g., in the textbook Explosives Technology; Spicak, Shnecek, or in the publication Primary Explosives; Matyas, Pachmaii, and in some scientific articles (Klapotke). The permanganate is herein reduced in two stages - to the green manganate virtually immediately after the contact with the hot, alkaline solution of 5-aminotetrazole and subsequently up to MnO2- this reaction is considerably longer. However, the mechanism of oxidative dimerization of two molecules of 5-aminotetrazole, producing two molecules of IH-tetrazole, linked through an azo group (- = -) has been clarified first after more than 100 years (Klapotke). Thiele originally wanted to oxidize the amino group to a nitro compound, but received quite a different product - a light yellow-colored (the azo group is a chromophore and all azo compounds are rich yellow- to orange-colored) disodium salt of 5, 5- AT in the form of pentahydrate. The oxidation mechanism of 5-aminotetrazole is as follows: a hydroxyloamino derivative is produced and linking of the two -NHOH groups with displacement of water results in linking of both nitrogens by a double bond providing an azo compound (a so- called “inner diazo”). Too intensive oxidation in the absence of alkali substances (a modification of the Thiele method in the sense of changing the order of dosage of 5- AT and the permanganate) provides, according to Klapotke, an oxo-azo tetrazole, but in a 16% yield only).

[0007] Carrying out of the reaction according to Thiele is as follows: solid KMnO4is added in small doses to a solution that is obtained by dissolution of 5-aminotetrazole in a great excess of ca. 15% NaOH (1 L of NaOH is used per ca. 1 mole of 5- aminotetrazole monohydrate) after heating up to 60 - 70°C under intensive stirring. The reaction is exothermic and the thermal course of the reaction is controlled by the dosage of the permanganate. The reaction temperature is left to reach 80 - 90°C and results in a brown suspension of amorphous MnO2in a full yellow solution of 5,5-bis- azotetrazole with pH of at least 13 - 14 (KOH is also produced during the reaction by decomposition of the permanganate). At the end of the reaction, a glass rod is used to withdraw a drop of the suspension and transfer it onto filter paper where the solution separates from the solid MnO2and the coloring of the paper in the circle around the brown MnO2is used to test whether the reaction suspension still contains unreacted 5-aminotetrazole - yellow coloring (then add some permanganate and repeat the test), or the coloring is green or pink - the solution contains unreacted manganate or the initial permanganate - then, the reaction is complete and the excess of the oxidant is removed with several ml of alcohol. Now, a hot suspension of MnO2in an extremely alkaline solution of 5,5-ATNa2is available and the critical stage of the process begins - due to an extreme dependence of solubility of ATNa2on temperature - very fine MnO2must be filtered off on a Buchner funnel as quickly as possible to avoid more profound cooling and great losses of the product, which crystallizes in the filter cake due to cooling. Besides, the highly alkaline solution at a temperature of about 90°C poses extreme requirements on filtering materials and even in laboratory preparation it frequently happens that the filter paper breaks and special filtering materials or double paper must be used - which extends the filtering time and makes the yield losses due to cooling logically higher. It is naturally possible to reduce the losses by multiple washing of the filter cake with very hot (preferably boiling) water, which, however, dilutes the resulting solution of ATNa2to such an extent that the product cannot be obtained by cooling any longer and the solution must be concentrated first with the use of a vacuum rotary evaporator - which makes the process more complicated.

[0008] The above-mentioned description clearly indicates that the implementation of this method in the production scale will lead to multiplication of the problems and the most powerful vacuum pumps or more pumps at the same time will have to be used as well as heated filtering funnels or nutch filters and substantially more resistant filtering materials, to say nothing of the use of industrial vacuum evaporators - which are machines with a very high energy consumption.

[0009] Besides all the said technological problems there is a principal problem - formation of a very high quantity of the side product - MnO2, contaminated by traces (in a bettercase) of ATNa2, which, while not explosive in the pentahydrate form, but e.g. heating during a metallurgical process will cause dewatering (at a temperature over 200°C) and formation of a disruptive explosive that is very dangerous to handle. MnO2would have to be processed chemically - e.g. dissolved in a mineral acid and converted to the respective manganese salt from which Mn would have to be separated out chemically or electrolytically (during the process, ATNa2is completely decomposed, producing the harmless 5-hydrazinotetrazole, which is decomposed by air oxidation into N2, CO2and water), which entails the necessity to introduce special treatment of wastewater.

[0010] With regard to the continuously increasing significance of the above-mentioned tetrazole derivative - namely mainly in the form of its organic salts (guanidine and its derivatives), as well the ammonium salt, as the main energetic components of gas generators and airbags, the development of new methods for producing the same appears to be extraordinarily beneficial. It is true that the classic Thiele method was, in spite of all the problems, introduced in the production scale in the U.S. (the use of coupled vacuum pumps, Teflon membranes, heating nutch filters etc.), but of course, the problem with accumulation of the unusable side product still remains. In the Czech Republic, pilot scale production of 5,5-AT was also introduced - in the form of its diguanidine salt under the trade name GzT - but this production has been discontinued for the above-mentioned reasons.

[0011] Specialized literature naturally offers a number of methods using very specific oxidants (mostly commonly unavailable) or metallic catalysts based on Pd (on active C) or nano gold (on a TiO2carrier) etc. Out of compounds, those proposed for oxidative dimerization of “(hetero)aromatics” include barium manganate, lead (IV) acetate, a mercury oxide (for photo oxidation), and mainly certain organic peroxides: t-Bu-hydrogenperoxide and t-Bu-hypoiodite (t-BuOI), sometimes replaced with a mixture of t-BuOCl with Nal - again, very “exotic” a commonly unavailable oxidants - moreover, mostly in organic solvents (DME, DMSO, DMF, CH3CN etc.); out of the more common ones NaOCl (which has also chlorinating effects), hyperactive I, further perbromates and periodates etc. Besides, most of the above-mentioned compounds are only active in oxidation of aromatic hydrocarbons and their derivatives (the simplest example being the oxidation of aniline to azobenzene). In tetrazole chemistry (in particular concerning oxidative dimerization of 5-aminotetrazole to 5,5- bis azotetrazole) - these are generally useless.

[0012] In addition, the selection of a suitable oxidant and the method using the same must be governed by specific requirements both for the initial product - 5-aminotetrazole, and for the final product - 5,5-bis azotetrazole. All derivatives of IH-tetrazole are acids, the strength of which (pKa) is given by the substituent in position 5 (in contrastto e.g. 5-aminobenzene - aniline, which is a weak base). Also, solubility in water and organic solvents is quite different (most aromatics dissolve in known organic solvents; 5-AT does not dissolve in most organic solvents except DMS and is very poorly soluble in water). The resulting 5,5-bis azotetrazole only exists in the form of its salts; in its free form (being displaced by stronger acids, including organic ones) it immediately decomposes into 5-HT (hydrazinotetrazole), formic acid and gaseous N2. 5-HT is strongly oxidizable and in an aqueous solution it completely decomposes after some time. Both the compounds (the initial 5-AT as well as the final 5,5-bis AT) form soluble salts with alkali metals (5-AT also forms soluble salts with most other metals as well as salts with organic bases - guanidines and its derivatives - in contrast to salts of 5,5-bis AT with other metals and organic bases, which are insoluble and salts of metals generally strongly hydrated).

[0013] The method should be based on the use of commonly available, relatively safe and non-toxic oxidants and should not produce any toxic waste, either soluble in wastewater (necessity to develop special treatment methods) or solid ones for which there will be no practical use (including non-toxic ones - such as MnO2in the Thiele method). Also, so-called “one -pot syntheses” are preferred, which are simple, singlevessel reactions where the product is separated in an insoluble form - from an aqueous solution - without the use of complex separation methods (extraction, ultrafiltration, centrifugation or vacuum evaporation etc.).

[0014] It has been found out in the course of many years of research, focused on said compounds, that aqueous solutions of 5,5-ATNa2are unstable and lead to formation of an unknown compound, the presence of which was unambiguously analytically confirmed at VSCHT (University of Chemical Technology) in Prague and the presence of which in the product is strongly undesirable (in precipitation with soluble salts of Bi, there is a significant change of product coloring, formation of extremely fine - unfilterable fractions and considerable impairment of the explosive characteristics of the resulting product).

[0015] For the oxidation of the alkaline solution of 5-AT at higher temperatures, oxidants based on inorganic and organic peroxides, certain peroxo compounds, and sodium hypochlorite were used. To detect the presence of azo compounds, the simple method of visual colorimetry was used - the change of the coloring of the colorless reaction solution (suspension) to yellow - did not occur at all in most cases of the reaction, or the azo compound was only detected in traces. The only exception was sodium hypochlorite, which caused a vigorous reaction under strong foaming, and the result was a deeply orange colored solution. In attempts at isolating 5, 5-AT in the form of an insoluble guanidine salt (a proven method at that time, working also in strongly alkaline environment) no precipitation occurred at all.

[0016] There exist various procedures also for laboratory preparation of BTH (by simple reduction of ATNa2), mostly based on reduction with elemental hydrogen (hydrogen “in statu nascendi”) and all these methods have been practically tested - unfortunately, they were found unsuitable for mass production again.

[0017] The most frequently reported method - by boiling of an aqueous solution with Mg chips under a reflux condenser (Klapotke reeports a reaction time of up to 20 h) - is too long, and in addition, it is impossible to exactly determine the completion of the reaction as the final product is a mixture of Mg(0H)2, possibly unreacted Mg and Mg salt of BTH (BTH is a free acid and is exceptionally chemically and thermally stable, which is quite rare among tetrazoles since most explosive tetrazoles are only known in the form of their metallic and organic salts). All salts of BTH - and mainly in alkaline environment (presence of Mg(OH)2) - are extremely prone to oxidation by air oxygen already - under a back formation of salts of 5,5-AT - yellow colored. The intensively yellow solution (suspension with Mg) will, at the beginning of the reaction, change to a yellowish suspension of the above-mentioned products that must be dissolved in concentrated HC1 and, after dilution, colorless BTH must be separated.

[0018] The reaction rate of this reaction - in a heterogeneous environment - can be substantially increased by using powdered Mg with the highest possible content of the active metal. However, practical tests have shown that the reaction is too vigorous (mainly in the initial stage), and the reaction suspension may even splash from the reaction flask.

[0019] A substantially better method is suggested again by Thiele - reduction with a solution of SnCl2in concentrated HC1. A hot saturated solution of AtNa2is poured into a calculated quantity (with a small excess) of SnCl2in HC1 and, in a few minutes, visible discoloration and a massive separation of BTH occurs. The reaction provides a yield of about 75% and is highly efficient. However, there is a problem with product purity - the obtained SnCl4partly decomposes in the excess of HC1, producing hexachloro stannic acid: SnCl4+ 2 HC1 = H2SnCl6(hexahydrate), which is well soluble in water. However, the latter is further hydrolyzed when diluted: H2SnCl6+ 3 H2O = H2SnO3+ 6 HC1, wherein the produced stannic acid (it can also be described as hydrated tin (IV) oxide - H2O + SnO2) is already insoluble in water but it dissolves in HC1. Therefore, the freshly precipitated BTH must be purified by dissolution in a great excess of concentrated HC1 and repeated precipitation with water (complete removal of SnO2is not successful and, after drying, SnO2does not dissolve in mineral acids either).

[0020] Besides the above-described problems, both the said methods use large quantities of concentrated HC1, which would represent another problem in bigger quantities to say nothing of the formation of a large quantity of gaseous hydrogen (in the first method).

[0021] In this case, a method using the insolubility of BTH in water at low temperatures, wherein BTH is directly separated from the reaction solution in a sufficiently pure form and will be usable in explosive mixtures without further treatment, will be preferred again.Summary of Invention

[0022] The solution according to the invention consists in finding a suitable oxidant, which must reliably work in a strongly alkaline environment and at the same time, it must be safe to handle, stable to store and commonly available in the market, as well as in setting optimum reaction conditions leading to the highest possible achievable yield, but not at the expense of technological complications, decrease of work safety or introduction of toxic compounds.

[0023] All these requirements are only fulfilled by one group of oxidants - at present commonly used in the “swimming-pool chemistry” and in various cleaning and bleaching agents - peroxodisulfates (persulfates) ! These compounds - in the form of soluble Na, K and NH4+salts - are currently produced in thousand ton quantities a year and they are encountered in cleaning and washing agents used in households.

[0024] The decomposition mechanism of these compounds in an aqueous environment, releasing elemental oxygen - in a strongly acidic, weakly acidic, neutral as well as alkaline environment - depending on temperature and concentration - has been examined in a very detailed way and it was found that the reaction rate did not essentially change in the pH range of 2 - 12 while it extremely rises in the range of 2 - 0 and 12 -14, and as the speed constant only depends on T and pH - it is a 1st order reaction. It is just the reaction rate in a strongly alkaline environment, where the reaction is catalyzed by the presence of OH anions, that is extremely important for our purposes - and the decomposition reaction can be put down as follows:

[0025] S2O82+ OH = SO52+ SO + H+,

[0026] where the SO52anion further decomposes by the reaction:

[0027] SO52+ OH = HO2+ SO

[0028] and the hydrogen peroxide anion further reacts with the persulfate ion:

[0029] S2O82+ HO2= SO4. + SO + O2. + H+,

[0030] where SO4. initiates a radical chain reaction, producing one elemental oxygen and two moles of hydrogen sulfate from 1 mole of PDS (wherein in an alkaline environment, hydrogen sulfates immediately pass into SO? and the oxygen radical can further react with PDS, producing another SO4. ion-radical.

[0031] The radical mechanism of the oxidation is extremely efficient, and therefore only PDS exhibited sufficient reactivity in the first experiments; and when initial conditions were set as in the Thiele oxidation, the reaction mixture turned significantly yellow already from the beginning of dosing of PDS under formation of the respective salt of 5,5-azotetrazole; however, strong foaming of the reaction mixture and development of gases occurred, which later turned out to be a negative accompanying phenomenon of the backward decomposition of 5,5-AT and of a substantial reduction of the reaction yield.

[0032] After a series of initial experiments, where all the 3 salts of PDS - ammonium, potassium and sodium, commonly available in the market, were gradually tested - the sodium salt has been chosen (the ammonium salt decomposes at higher temperatures and it is not possible to maintain sufficiently high pH in the solution; and potassium sulfate, as the decomposition product of the potassium salt of PDS, is poorly soluble in the mother solution and it co-precipitates with salts of 5,5-AT, which leads to false yield values.

[0033] Hundreds of experiments have been conducted with the aim to set optimum reaction conditions (the way and order of adding the oxidant into the alkaline solution of 5- AT, increasing the reaction temperature and the reaction time as well as the separation methods of the product from the reaction suspension and mainly a thorough separation of the other anions - mainly sulfates, which was performed by precipitation of the sodium salt of 5,5-AT in the form of much less soluble guanidine salt - GzT - directly from the reaction solution). However, the yields still did not exceed the limit of 30, max. 35%.

[0034] The stoichiometric quantity of the alkali for this reaction was set to 3 moles of NaOH to 1 mole of 5-AT and this quantity was increased by 100 % and the initial reaction conditions were set as in the Thiele method. A series of experiments was conducted with the aim to ascertain the influence of the concentration and the amount of substance of the base used on the reaction yield. The use of ca. 2x more concentrated base led not only to simultaneous separation of Na2SO4(x H2O), but also to a substantial reduction of the yield to 15 - 20% whereas a concentration reduction - gradually to 2 M, 1 M and 0.5 M (together with a reduction of the excess of the base) - led to a gradual increase of the yield, to 35 - 40 - 45 - 50%. These experiments indicate that the undesired side reaction that causes backward decomposition of the product strongly depends on the concentration of the reaction solution and can be partly suppressed by reduction thereof. Of course, further reducing of the concentration would be inefficient from the technological point of view and the yield increase would be at the expense of decreasing the “recovery ratio”.

[0035] The stoichiometric quantity of PDS was calculated to be 1 mole per 1 mole of 5-AT monohydrate and it was established that using bigger excesses of the oxidant, which is common in oxidation-reduction reactions, has an opposite effect here and causes subsequent undesired decomposition of the product. Therefore, the excess of PDS should not be higher than of the order of a few %.

[0036] It has been further found that the reaction rate extremely depends on the reaction temperature, and thus after further increasing of the reaction T from 90 to 98 - 100°C, the yield rises up to values exceeding 60 % (the value of 67 % was achieved!).

[0037] Isolation of the product from the reaction solution by precipitation in the form of GzT, which exhibits about 0.5% solubility in water at 25%, is a relatively efficient method, but because multiple washing with water is necessary to completely remove the sulfate ions, the reaction suspension and the washing water must be cooled down as much as possible (best to as low as 0°C), which could be a technological problem, a product isolation method has been developed under simultaneous reduction with ascorbic acid and formation of BTH, which is extremely insoluble in cold water and can be repeatedly washed with cold water without incurring measurable losses. The separation rate of BTH after dosing of ascorbic acid is a measure of the achieved yield - if the separation occurs in the discoloration stage already (2 - 3 min), the yield will exceed 60%.

[0038] This energetic composition is itself one of the main energetic components of our new environment-friendly priming mixture (according to patent CZ 308125, also published as CZ 2018-408 A3) and if it is converted to a solution with a suitable base, it can be oxidized again without problems to the respective salt of 5, 5- AT (in this case common oxidants - such as H2O2- can be used or simply the solution can be bubbled with the air, or better, oxygen).

[0039] The yields of both the reactions - reduction with ascorbic acid and the subsequent oxidation - reach more than 80%.

[0040] Accordingly, the invention provides a process for producing soluble salts of 5,5- azotetrazole (5, 5-AT) by oxidation of 5 -amino tetrazole with a soluble peroxodisulfate in a strongly alkaline environment and at an increased temperature, which process comprises the following steps: a. the base is charged in the reaction vessel in the stoichiometric quantity; a. the temperature is set to 98 - 100°C; b. the dosage is only performed after the required temperature is achieved in the order of PDS and, after dissolution, 5-AT; c. both the reactants are dosed in the solid form;d. the course of the reaction is checked using the visual colorimetry method, continuous pH measurement and a drop reaction of the sampled solution with a solid permanganate; e. the reaction is complete when the originally colorless solution of the sodium salt of 5-AT gradually acquires rich yellow-orange color and pH starts to decrease from the original value of 12.5 - 13 to the neutral value. At this stage, the solution is alkalized again by addition of the base and the procedure is repeated until stabilized value of 9-10 is reached, which indicates that all the PDS has reacted. To check whether all the 5-AT has reacted, a few drops of the reaction solution are sampled and a drop reaction with a permanganate crystal is employed to confirm completion of the oxidationreduction reaction; f. after the reaction solution cools down - still under intensive stirring - to 40 - 50°C, 5, 5-AT is separated, by precipitation with a small excess of solid guanidine chloride, as a poorly soluble bis guanidine salt (GzT), which will fill the entire volume of the reaction vessel during further cooling to the room temperature; g. in case of a negative result, the product is aspirated and, after washing with acetone and the final aspiration, it is filtered and dried.

[0041] The base is a 0.5M solution of sodium hydroxide here.

[0042] Sodium peroxodisulfate acts as the oxidant here.

[0043] Another object of the invention provides a process for producing 5,5-bis-tetrazolyl hydrazine (BTH) by reduction of solutions or suspensions of 5, 5-AT salts with ascorbic acid, which process comprises the following steps: a. the reduction can also be conducted directly in the reaction solution after oxidation of 5-AT with the persulfate in the above-mentioned manner after cooling to 40-50°C; b. ascorbic acid is dosed in the solid form in a weight quantity of ca. 2.5 - 3 / 1 (5,5-ATNA2pentahydrate); c. the final pH should be within the range of 3 - 3.8; d. completion of the reaction is manifested by complete discoloration of the reaction solution under precipitation of a white, well sedimenting product, which occurs during several minutes after the dosage of ascorbic acid; e. with regard to high insolubility of the product, vacuum filtration can be carried out at a normal temperature and multiple washing can be employed to remove all impurities without causing a substantial yield loss.

[0044] Accordingly, BTH fulfills not only the function of a separate energetic constituent with a high content of nitrogen, but also the function of an optimum separation form of the hydrazo derivative of 5,5-AT, which can be easily oxidized back to salts of 5,5-AT.

[0045] The re-oxidation of BTH to salts of 5,5-AT with gaseous oxygen is carried out by a process comprising the following steps: a. BTH is converted to a soluble salt by reaction with a calculated quantity of a solution of a base; b. the solution is quantitatively transferred to a washer with a frit bubbler; c. oxygen is bubbled until a richly yellow solution is obtained, which is accompanied by precipitation of crystals of the sodium salt of 5,5-AT; d. as the oxidation efficiency gets weaker with the increasing product concentration, the reaction is terminated at this stage and the filtrate, after precipitation of 5,5-AT in the form of GzT in the above-mentioned way, is used repeatedly.

[0046] Any alkali metal hydroxide in IM concentration or a concentrated ammonia solution can be employed as the base.

[0047] If ammonia is used, the separation form of 5,5-AT is represented by the anhydrous ammonium salt, almost insoluble in ammonia, which represents the final product when this method is used.

[0048] BTH can also be oxidized with a 30 - 40% solution of H2O2using a process comprising the following steps: a. the BTH solution is prepared in the above-mentioned manner; b. after heating to T of 80 - 90°C, concentrated H2O2is dosed dropwise; c. the course of the reaction is checked using the visual colorimetry method, the temperature increase after addition of the peroxide and the drop reaction as mentioned above, d. the end of the reaction is manifested by a color change to richly orange and the formation of a thick suspension of the sodium salt of 5,5-AT pentahydrate; e. product isolation as GzT as mentioned above.Examples

[0049] Oxidative dimerization of 5-aminotetrazole to sodium 5,5-bis-azotetrazolate:

[0050] The calculated quantity of 0.5M NaoH is charged in a heated reaction kettle, equipped with a high-speed stirrer, thermometer and pH meter and heated up to the temperature of 98 - 100 °C under continuous stirring. After reaching the desired temperature the calculated quantity of sodium persulfate in an excess of several percent is added in several larger doses, followed, after dissolution, with the calculatedquantity of 5- AT. The reaction starts under abundant development of gases (occurrence of a large quantity of microbubbles) within a few minutes after dissolution of 5-AT, which is manifested by the reaction solution becoming yellow, which gets ever more intensive, and within an hour - under continuous stirring and maintaining the reaction temperature just below 100°C - the coloring intensity continuously increases, passing into rich orange. At this stage, there is also a decrease of pH from the initial 13 - 13.5 to the neutral value - which indicates reacting of the stoichiometric quantity of the persulfate and the solution needs to be alkalized again and the further course of pH should be monitored. After further decrease, the solution is alkalized again and if pH does not change any more - it indicated that all the persulfate has reacted - the reaction should be completed, which is confirmed using a drop reaction: on a white drop plate, a few crystals of KMnO4are placed and a few drops of the reaction solution are added. If the drop turns red, it means that the solution does not contain 5-AT, which would reduce the permanganate, and the reaction is completed (otherwise the drop would become dark green - presence of the manganate).

[0051] The heating is switched off and the reaction mixture is left to cool down to 40 - 50°C under continuous stirring.

[0052] Isolation of 5,5-azotetrazole as GzT:

[0053] Since GzT is ca. 10 times less soluble than the sodium salt of 5, 5-AT pentahydrate- as the separation form of 5, 5-AT - it is much more suitable, and therefore a small excess of the calculated quantity of solid guanidine hydrochloride is added to the cooled down solution under intensive stirring. Due to its exceptional solubility in water it is dissolved virtually immediately, and light yellow, very voluminous GzT precipitates, filling the entire reaction vessel. Under continuous stirring, the resulting suspension is cooled down to a temperature close to 0 and, after settling, the product is aspirated on a Buchner funnel or nutch filter (with the use of common filter materials) and washed with icy water several times (before complete aspiration, a sample must be taken into a test tube, dissolved in ca. IM of HC1, heated up until discoloration, and a few drops of a 20% solution of BaCl2must be added - the sample must not get turbid as this would mean presence of sulfates and another washing with water would have to follow! Logically, further washing reduces the yield of GzT! After the aspiration, washing with acetone and drying, the product is ready for use.

[0054] Since GzT (similarly to the sodium salt - see patent CZ 308125) will be used to precipitate BiBA (Bismuth Basic Azotetrazolate - alkaline azo tetrazolate of Bi), the presence of any cations which Bi3+ions precipitate as highly insoluble “oxo salts” is undesirable, and therefore perfect washing is essential!

[0055] Reduction of 5, 5-AT to BTH directly in the reaction solution:

[0056] Since BTH is still at least 10 times less soluble in water than GzT and its solutions in alkalis are strongly oxidizable (they turn yellow already by the action of the atmospheric oxygen, again producing 5,5-AT), the method of reducing 5,5-ATNa2with ascorbic acid, which is incomparably simpler than the existing methods, has been successfully tested:

[0057] Solid ascorbic acid is dosed into the cooled down reaction solution under intensive stirring in the weight ratio of ca. 2.5 / 1 (based on 5,5-ATNa2pentahydrate). The reduction is manifested by intensive discoloration, which is completed in the course of several minutes and at this stage already, intensive separation of white, finely crystalline BTH starts, which is completed roughly within an hour (under continuous cooling of the mixture to the ambient temperature). Final pH should be in the range of 3 - 3.8. After settling and letting the product stand, the product can be filtered and even multiple washing with water will not decrease the yield in a measurable way. After aspirating, washing with acetone and drying, the product is ready to be used in new priming mixtures and for optional re-oxidation back to 5,5-ATNa2and subsequent isolation in the form of GzT or ammonium salts.

[0058] BTH produced in this way can be either used in a priming mixture without further treatment (see patent CZ 308125) or using re-oxidation it can be converted to very pure GzT or ammonium salts (there is no risk that sulfates will be present), the starting product for the production of BiBA (Bismuth Basic Azo tetrazolate).

[0059] Oxidation of BTH with gaseous oxygen or H2O2:

[0060] BTH is characterized with extraordinarily low solubility in water and well-known organic solvents (except DMSO) and, as a free acid, it forms a number of salts - salts of alkali metals or the ammonium salt conversely exhibit high solubility and BTH can, in the form of these dissolved salts, be easily oxidized back to salts of 5,5-AT with the use of common oxidants.

[0061] Oxidation with oxygen:

[0062] 2 moles of NaOH are consumed per 1 mole of BTH- i.e. 2 L of 1 M NaOH. The measured quantity of 1 M NaOH is charged in a vessel and the calculated quantity of BTH is dissolved under continuous stirring. A clear, weakly yellowish solution of BTH Na2is obtained and final pH should be slightly alkaline). The solution is quantitatively transferred into a washer (for the laboratory scale, e.g. a washer by Drechsler with a frit extension) and pure oxygen is introduced directly from the bottle. After about an hour, the solution is intensively yellow and 5,5-ATNa2starts to precipitate in the form of well-developed crystals. Bubbling is continued for about another hour and then the solution is quantitatively transferred into a vessel where water is added under intensive stirring until complete dissolution of 5,5-ATNa2, followed by dosing the calculatedquantity of guanidine hydrochloride. GzT starts to precipitate within a few seconds and voluminous precipitate will fill the entire vessel, forming a thick, light yellow suspension (the stirrer must be very powerful!). After thorough stirring, the product is left to settle and then filtered with the use of common filtering material (e.g. filter paper - red tape), washed with water several times, aspirated, washed with acetone and dried after the final aspiration.

[0063] The filtrate is saved and the whole process repeated 2 more times (before the last filtering, the suspension is cooled as close to 0 °C as possible and washed with icy water - to avoid higher losses!). Optimally, multiple washers are used, connected in series.

[0064] The total yield (after summing the weights of all 3 products) reaches ca. 85 - 90%.

[0065] A concentrated aqueous solution of ammonia can also be used as the base. The molar ratios are the same as in the case of NaOH and, after conversion to 30% “ammonia water”, ca. 100 g (90 ml) is consumed per 1 mole of BTH. The solution may be slightly alkaline. During the oxygen bubbling, a thick suspension of a richly yellow, crystalline ammonium salt is formed that is very poorly soluble in ammonia, such that the oxygen bubbling is more efficient than in the case of producing the at least 10 time more soluble sodium salt, because the product is continuously intensively separated from the reaction solution and besides, during the isolation of the product by means of vacuum filtering, no washing with water is necessary (the reaction suspension does not contain any ions - apart from NH4+), so a rinse with ammonia water on the filter and then, after aspiration, with methanol, in which ammonia dissolves well, is sufficient (the ammonium salt of 5,5-AT is insoluble in methanol!).

[0066] The ammonium salt of 5,5-AT is anhydrous, both chemically and thermally highly stable, safe to handle and very well usable for the production of the Bi salt of 5,5-AT (BBiAT).

[0067] Oxidation with H2O2:

[0068] The preparation of the BTH solution is conducted as in the preceding case. The resulting solution is heated up to 80 - 90°C under intensive stirring while it gradually - due to oxidation by atmospheric oxygen - acquires a rich yellow color. After achieving the reaction temperature, 30-40% H2O2starts to be added dropwise - which causes intensive foaming and the temperature immediately rises by 10 - 15 °C (depending on the addition rate of the peroxide). During several minutes, the solution is colored light orange and at the same time it starts to become turbid by precipitation of 5,5-ATNa2until a thick suspension of the product is obtained. The reaction is completed when there is no further significant temperature increase after addition of H2O2and the drop test using a permanganate crystal does not provide the brown MnO2any more, but theresulting suspension is reddish purple (in this case, the green manganate is not formed - pH is only slightly increased). The theoretical quantity of H2O2is 1 mole per 1 mole of BTH (in the case of common 30-35% peroxide this corresponds to ca. 50 ml per 1 mole of BTH) - in practice at least a 5-10 fold excess needs to be used.

[0069] The resulting suspension is then diluted with distilled water to a double volume under intensive stirring (until complete dissolution of all the product and formation of a clear, intensively yellow solution). Then, the calculated quantity of guanidine hydrochloride is dosed into the cooled down solution having a temperature of 40 - 50°C under intensive stirring. Almost immediately, a thick, light yellow precipitate of GzT is formed, which fills the entire volume of the reaction vessel. The suspension is cooled down to 0 °C, aspirated on a Buchner funnel or nutsch filter, washed with icy water several times and finally with acetone and after final aspiration the product is dried.

[0070] The yield varies in the range of 80 - 85%.Industrial Applicability

[0071] The invention can be applied to the production of explosive tetrazole derivatives usable as precursors for the production of further explosive derivatives of tetrazoles (GzT, ammonium salt - for the production of a new explosive based on Bi - CZ 308125) and in mixtures for gas generators), as well as tetrazole derivatives that fulfil the function of secondary explosives or highly energetic constituents in new priming mixtures - BTH (see CZ 308125).

[0072] Applicability to ammunition production - production of priming mixtures for center fire as well as rim fire, production of gas generators and various types of propellants.

Claims

Claims

1. A process for producing soluble salts of 5,5-azotetrazole by oxidation of 5-aminotetrazole, characterized in that it comprises the following steps: a. a strong alkali is charged in the reaction vessel in the stoichiometric quantity; b. the temperature is set to 98 - 100°C; c. when the said temperature has been reached, a soluble peroxodisulfate is added and, after its dissolution, 5- aminotetrazole is added, both the reactants in the solid form; d. after the originally colorless solution gradually becomes richly yellow-orange and pH starts to decrease from the original value of 12,5 - 13 to the neutral value, the solution is alkalized again by addition of a strong base and the procedure is repeated until pH is stabilized on the value of 9-10, which indicates that all the peroxodisulfate has reacted; e. optionally, to check whether all the 5-aminotetrazole has reacted, a few drops of the reaction solution are sampled and a drop reaction with a crystal of permanganate is employed to confirm completion of the oxidation-reduction reaction; f. after cooling of the reaction solution - still under intensive stirring - down to 40 - 50°C, 5,5-azotetrazole is separated, by precipitation with a small excess of solid guanidine chloride, as a poorly soluble bis guanidine salt of 5,5-azotetrazole; g. after further cooling to 0 °C, the precipitate is subjected to vacuum filtering and after being washed with icy water several times a sample is taken to test the presence of sulfates, h. in case of a negative result, the product is aspirated and after washing with acetone and the final aspiration it is filtered and dried.

2. The process according to claim 1, characterized in that the strong base is a 0.5M solution of sodium hydroxide.

3. The process according to claim 1, characterized in that the peroxodisulfate is sodium peroxodisulfate.

4. A process for producing 5,5-bis-tetrazolylhydrazine by reduction of solutions or suspensions of 5,5-azotetrazole obtained by the process of claim 1, characterized in that it comprises the following steps: a. ascorbic acid in the solid form is dosed to the solution or suspension of 5,5-azotetrazole, preferably to the solution cooled down according to point d) of claim 1 to 40 - 50°C, in a weight amount of 2.5 - 3 / 1, based on the disodium 5,5-azotetrazole pentahydrate; b. the reaction is carried out until complete discoloration of the reaction solution under precipitation of a white, well sedimenting product; c. the product is isolated by filtering, preferably vacuum filtering.

5. A method of re-oxidation of 5,5-bis-tetrazolylhydrazine to 5,5- azotetrazole, characterized in that it comprises the following steps: a. 5,5-bis-tetrazolylhydrazine is converted to a soluble salt by reaction with a calculated quantity of a solution of a base; b. oxygen is bubbled through the solution until a richly yellow solution is obtained, which is accompanied by precipitation of crystals of the sodium salt of 5,5- azotetrazole; c. as the oxidation efficiency gets weaker with the increasing product concentration, the reaction is terminated at this stage and the filtrate, after precipitation of 5,5-azotetrazole in the form of the bisguanidine salt according to point f) of claim 1, the filtrate is used repeatedly.

6. The method according to claim 5, characterized in that the base is an alkali metal hydroxide, or a concentrated solution of ammonia.

7. The method according to claim 6, characterized in that the product is the ammonium salt of 5,5-azotetrazole.

8. A method of re-oxidation of 5,5-bis-tetrazolylhydrazine to 5,5- azotetrazole, characterized in that it comprises the following steps:a. 5,5-bis-tetrazolylhydrazine is converted to a soluble salt by reaction with a calculated quantity of a solution of a base; b. after heating to a temperature of 80 - 90°C, concentrated hydrogen peroxide is added dropwise; c. the reaction is carried out until the color changes to rich orange and a thick suspension of the sodium salt of 5,5- azotetrazole pentahydrate is formed; d. 5,5-azotetrazole is precipitated in the form of the bisguanidine salt according to point f) of claim 1.