MXPA97003065A - Improved process for the preparation of 5-aminotetra - Google Patents

Abstract

The present invention relates to a process for producing 5-aminotetrazole, characterized in that it comprises: a) reacting a salt of aminoguanidine of a mineral acid with a diazotization agent to form the corresponding guanilazide salt, the diazotization agent being selected from the group which consists of: i) nitrous acid which is produced in situ by the reaction of a mineral salt with a nitrite salt, the reaction being controlled to ensure the consumption of substantially all nitrous acid, when formed and thereby substantially exclude the presence of ions nitrite-free, and ii) an alkyl nitrite, and b) cyclize the guanilazide salt to 5-aminotetraz

Description

IMPROVED PROCESS FOR THE PREPARATION OF 5-AMINOTETRAZOL Description of the invention This invention relates to the production of 5-amino-tetrazole.

More particularly, the invention relates to improvements in the manufacture of this valuable chemical compound, including a process that is carried out in a container, for the commercial manufacture of 5-aminotetrazole in an economical manner and in improved quality and yield. The 5-aminotetrazole compound, which is referenced hereinafter, alternatively by the abbreviated name "5-ATZ", is a well-known chemical intermediate which is also used in the manufacture of propellants. In recent years, it has found utility in an increased number of non-military applications which include, for example, the production of automotive airbags. However, only limited information has been published in the technical literature regarding the methods to synthesize 5-ATZ.

Briefly, according to the previous technique dating from 1901, the 5-ATZ can be synthesized by one of two routes which are described in two old German publications. The first involves the diazoation of aminoguanidinium nitrate with sodium nitrite and nitric acid to form a guanylylide salt intermediate, which is then cured by heating in the presence of sodium acetate to 5-amino-tetrazole. See Thiele, Ann. 270, 54 (1892).

REF: 24412 The second method, according to the prior art, to produce 5-ATZ, reacts the hydrazoid acid, sodium azide derivative and an acid with cyanamide or didandiamide. See Hanstsch and Vogt, Ann. 314, 339 (1901). These prior art methods are not appropriate for the economically feasible, efficient production of 5-ATZ on a commercial scale. In addition, the product of the first method is commonly plagued with objectable yellowish discoloration, the removal of which substantially adds to the manufacturing cost of 5-aminotetrazole. Now, an improved process has been developed for the application of 5-ATZ in high yield and purity. In addition, the process of the invention is particularly adapted for use as an economically feasible route for the production of 5-ATZ on a commercial scale. According to the invention, 5-ATZ, which is substantially free of discoloration, is prepared by a process which comprises: (a) reacting an aminoguanidine salt with a diazotiation agent to form the corresponding guanilazide salt, The diazoating agent is selected from (i) nitrous acid, which is produced in situ under controlled conditions and (ii) an alkyl group; and (b) cyclizing the guanilazide salt to 5-aminotetrazole. According to another embodiment of the invention, an improved process for the production of 5-ATZ is provided, which process is particularly adapted for use as a process carried out in a container and comprising: (1) reacting together the cyanamide with a hydrazine salt, that is, the product of the reaction of hydrazine with a mineral acid to form the corresponding aminoguanidine salt; (2) diazoate the aminoguanidine salt to the corresponding guanilazide salt; and (3) cyclizing the guanilazide salt to 5-aminotetrazole. In addition, according to the invention, improvements and refinements are provided which can be used in any process that uses the sequence of stages summarized above to produce pure 5-ATZ economically and in high yields. As indicated above, the production of 5-ATZ is obtained by reacting an aminoguanidine salt with a diazoadon agent to form the corresponding guanilazide salt, which is then cyclized to 5-ATZ. The aminoguanidine salt can be obtained from any appropriate source or synthesized by an appropriate method. According to the preferred embodiments of the invention, it is prepared by reacting the corresponding hydrazine salt with cyanamide, the foregoing being the product of the reaction of hydrazine with a mineral acid. All of these reaction steps, which are preferably carried out in an aqueous medium, are described in more detail below.

As used in the preparation of the hydrazine salt, the hydrazine can be hydrated or anhydrous. However, for reasons of economy and practice, it is preferable to employ an aqueous solution of hydrazine in any suitable concentration, such as from about 20 to about 70, and preferably about 30 to about 64, percent by weight. As for the acid, this can be any appropriate mineral acid. The illustrative acids are hydrochloric, hydrobromic, nitric and sulfuric, the corresponding hydrazine salts of which are chloride, bromide, nitrate and hydrazinium sulfate respectively. Preferred acids are hydrochloric, hydrobromic and nitric acids, hydrochloric acid is the most preferred. As is the case with hydrazine, the concentration of the mineral acid can be varied over a reasonably wide range. Typically, commercially available concentrations may be used as such or they may be diluted with water to any appropriate concentration. For preaching reasons, the concentration of the acid preferably should not be less than about 20 weight percent, such as from about 25 to about 35 and most preferred 28 to 32 weight percent. In accordance with the practical embodiments of the invention, the concentrations of the hydrazine solvate and the acid solution should be selected such that the resulting hydrazine salt solution would have a concentration of about 30 to about 40 and more preferably about 32 to about 26 weight percent.

In preparing the hydrazine salt, any molar ratio of mineral acid per mole of hydrazine can be used. However, as a preaching issue, since the reaction involves equimolar proportions of the two starting materials, it is preferable to use from about 0.80 to about 1.05 moles of acid per mole of hydrazine. According to a particularly preferred embodiment of the invention, not more than one mole of the acid, such as from about 0.85 to about 0.98 and still more preferably about 0.92-0.97 mole, is used per mole of hydrazine. This is based on the discovery that when the hydrazine salt is reacted with the cyanamide, the reaction proceeds faster and with maximum conversion to the corresponding aminoguanidine salt, when a small excess of free hydrazine is present. Thus, according to this preferred embodiment, the reaction of the hydrazine salt with the cyanamide is effected in the presence of a small amount of free hydrazine and a convenient way to achieve this is to use, when preparing the hydrazine salt, an excess of hydrazine over the preferred stoichiometric amount for the reaction with the acid. Usually, a small fractional excess is sufficient to achieve the desired objective. The reaction of hydrazine with the mineral acid can proceed at any appropriate temperature, such as from about 0 to about 100 ° C. However, since the reaction is exothermic, to avoid excessive heat which can lead to the loss of some hydrazine, some cooling may be necessary or desirable, such as to maintain an reaction temperature no greater than about 60 ° C, such as about 10 to about 50 ° C and more preferably about 20-40X. Any suitable conventional means for effecting cooling may be employed. The cyanamide, preferably in aqueous solution of any suitable concentration, such as from about 40 to about 60, preferably about 45 to about 55 percent by weight (the commercially available 50% concentration is most preferred) is added to, and reacted with, the hydrazine salt in any appropriate relative molar ratio. Since the stoichiometry of the reaction requires equimolar proportions of the two reactants, ordinarily a range of from about 0.8 to about 1.2 moles of cyanamide are used per mole of hydrazine salt. According to the preferred embodiments, the proportion of cyanamide used is determined in relation to the total hydrazine present, that is, the free hydrazine also as the hydrazine salt; and for each mole of total hydrazine, cyanamide is used in a ratio ranging from about 0.88 to about 1.12, most preferably about 0.95-1.05 moles per mole of the total hydrazine. In carrying out the aminoguanidine salt formation reaction, elevated temperatures greater than about 40 ° C are used, such as from about 50 to about 100 °, preferably about 70-90 ° C and most preferably about 82-88 ° C. From the process point of view, the reaction can be effected, for example, by first heating the hydrazine salt solution to a temperature within the desired range and then adding the cyanamide, the desired temperature being maintained until the reaction is consumed. If the hydrazine salt is the hydrochloride, the reaction can be illustrated by equation I as follows: NH I N2H4 * HCI + H2NCN - > H2NCNHNH2 * HCI (I) The reaction product, which consists mainly of an aqueous solution of the aminoguanidine salt, is then reacted with a diazoation agent to form the corresponding guanylylide salt. Preferred diazoning agents according to the invention are nitrous acid and alkyl nitrites. The use of the latter is preferred when the process of the invention is implemented by using a multi-reactor system, which would be particularly suitable for a continuous process operation, since it has been found that by nitrating the aminoguanidine salt with a nitrite of alkyl has the desirable result of producing a final 5-ATZ product, which is exceptionally clean and substantially free of discoloration. On the other hand, the use of nitrous acid, according to another preferred embodiment of the invention, has the advantage of not requiring a separate reaction vessel to generate this diazoation agent. As such, the use of nitrous acid would be particularly appropriate, although not limited, to a single-stream operation or vessel processes, to manufacture 5-ATZ. Nitrous acid is generated in situ by conventional methods such as by the reaction of an acid with a nitrite salt. Any appropriate acid and nitrite salt can be used. Illustrative acids are general acids including, for example, hydrochloric, hydrobromic, nitric and sulfuric acids; and illustrative nitrite salts include alkali metal and alkaline earth nitrites, alkali metal nitrites such as sodium and potassium nitrite are preferred. For reasons of economy and practical issues, it is particularly preferred to react the hydrochloric acid with the sodium nitrite, usually in aqueous solution to generate the nitrous acid. Any appropriate relative molar ratio of the acid and nitrite can be used, but in actual preaching approximately equimolar amounts are used and although there is no specific temperature or range of temperatures at which the reaction will proceed, it is preferred to carry out the reaction at a temperature of about 10 ° C to about 30 ° C, more preferably about 15 ° C to about 25 ° C, in order to substantially avoid the presence of any side reactions. Since the reaction is exothermic, cooling may be required to control the temperature within these preferred ranges and any conventional cooling means may be used for this purpose. When emulating the in situ generation of nitrous acid it is preferable to first add the mineral acid to the aqueous aminoguanidine salt solution. followed by the gradual addition of the nitrite salt. According to the invention, it is particularly advantageous to control the rate of addition of the nitrite salt, in such a manner as to substantially prevent the presence of free or excess nitrite ions in the solution. That is, the rate of addition of the nitrite should preferably be gradual or regulated to ensure substantially complete consumption or reaction of the nitric acid, as it is formed with the aminoguanidine salt. This preferred process is important in view of the discovery according to the invention that by minimizing or preventing the presence of nitrous oxide which did not react, it has a beneficial effect on the purity or reduction of the discoloration of the final 5-ATZ product. Any suitable conventional method can be used to verify the solution, in order to implement this preferred method, such as the use of the oxidation of iodide to iodine in a stain plate. It is also desirable in certain instances to effect in situ generation of the nitrous oxide in the presence of an alcohol, for example, ethanol, which serves as a modifier. The diazoation reaction can be represented by the following equation, where the aminoguanidine salt is aminoguanidinium chloride: NH NH || • | H2NCNHNH2.HCI + RN02 - > H2NCN3 * HCI + H20 + ROH (II) in which R is hydrogen or an alkyl group. Thus, when nitrous acid is used as the diazoating agent (R = H), water (2 moles) would be a secondary product; whereas if an alkyl nitrite (R = alkyl) is used, the byproducts are one mole of water and one mole of alcohol. With respect to the alternative alkyl nitrite diazoning agent, which is used according to the invention, this may be any such appropriate nitrite. In general, the alkyl nitrite can be represented by the formula RNO, wherein R is alkyl, generally having not more than 8 and preferably not more than 6 carbon atoms, such as methyl, ethyl, propyl, butyl , pentyl and hexyl. Particularly preferred are alkyl nitrites having up to 4 carbon atoms, methyl and ethyl nitrites are most preferred. The alkyl nitrite can be obtained from any suitable source or can be prepared by any suitable method. Conveniently it is produced by the reaction, preferably in a separate reactor, of an alcohol with a nitrite salt in the presence of a mineral acid and then added to the aminoguanidine salt solution. The alcohol can be a primary, secondary or tertiary alcohol and the nitrite salt can be any of such appropriate salts, of which the alkali metal nitrites are illustrative. Further details concerning the preparation of the alkyl nitrites can be found, for example, in U.S. Patent No. 2,615,896 and in Colé, Organic Syntheses, Vol. 2 (1943), p. 204, both of which are incorporated by reference herein.

Advantageously, an alcohol having 1 to 6 carbon atoms is reacted with an alkali metal nitrite, for example, sodium nitrite, by using from about 0.8 to about 2.0 moles of alcohol per mole of nitrite, the reaction is effected. with the addition of an appropriate mineral acid. To the extent that the lower alcohol nitrites are either gases or liquids with low boiling point, they are preferably bubbled into the solution of the aminoguanidine salt; while this precaution is ordinarily unnecessary when a liquid, more stable, higher alkyl nitrite is used. When an alkyl nitrite is used as the diazoation agent, it has been found that the diazoadon reaction proceeds more rapidly in the presence of a dry medium. Therefore, the addition of a bond, for example, a mineral acid before or after the start of the diazoation reaction is recommended, the proportion of such acid addition can be determined by systematic experimentation on a case-by-case basis. The diazoation reaction is carried out at any appropriate temperature. Normally a temperature of less than about 60 ° C, such as from about 0 to about 50 ° C, preferably from about 8 to about 30 ° C and higher preferred about 12-20 ° C. Next to the diazoate of the aminoguanidine salt to the corresponding guanilazide salt, the latter is cured to form the 5-aminotetrazole as illustrated in equation III below, in which the cidization is effected in the presence of ammonia: NH N - N I I I H2NCN3 * HCI + NH3 > C N + NH4CI (III) / \ / H2N N H The cyclisation step is obtained at elevated temperatures and by raising the pH of the guanylyl salt salt solution by means of a base. For this purpose, any of a wide variety of suitable alkaline materials may be used, which include, for example, ammonia, a hydroxide, acetate or carbonate of an alkali metal or alkaline earth metal. Preferred bases are ammonia and sodium or potassium hydroxide, acetate or carbonate, ammonia being the most preferred. Such a ratio of the base is used to raise the pH of the guanilazide solution to at least about 4., such as from about 4 to about 6.5 and preferably from about 4.2 to about 6 0. A more preferred pH range of about 4.5 to about 58 is recommended to obtain an optimum conversion ratio to 5-ATZ. The exact amount of the base which is required can be determined by systematic experimentation, depending on the particular base which is used and the desired pH. So, for example, to obtain a pH of about 5.5 when using ammonia. about 1.3 moles of ammonia would be required per mole of guanilazide salt. As indicated above, the cyclization step is effected at elevated temperatures, for example, greater than about 40 ° C, such as from about 50 to about 125 ° C, preferably about 80-110 ° C, and most preferably approximately 95-105 ° C. The product of the cyclization reaction usually comprises an aqueous solution of 5-ATZ and subproduct salt, for example, ammonium doride when ammonia is used as the base. The isolation and recovery of 5-ATZ can be obtained by any appropriate or conventional means. Ordinarily, precipitation of 5-ATZ can be effected by cooling the mixture of the reaction product to about 55 ° C or a lower temperature. However, a pH of more than about 5 has been found, the precipitation of 5-ATZ is not complete, that is, some of the 5-ATZ in the form of the salt thereof remains dissolved. On the other hand, at a pH less than 3.0, the amphoteric 5-ATZ would form a more stable salt with the strong acid present. Therefore, to optimize the isolation and recovery of the product according to the invention, it is preferable to adjust and maintain the pH from about 3.5 to about 4.5. It is also preferable to effect the cooling of the reaction product mixture gradually in order to avoid very sudden and rapid precipitation of 5-ATZ and thereby minimize the presence of impurities in the product.

The precipitated product of the invention process is a crystalline whitish 5-aminotetrazole, monohydrate, which is quite pure and substantially free of discoloration. As such, no costly or annoying operation is necessary to purify it or improve its appearance. If desired, the hydration water can be easily removed by heating for several hours at a temperature greater than about 100 ° C. As indicated above, according to a preferred embodiment of the invention, a process is provided that is carried out in a vessel for the efficient and economical production of the high quality 5-ATZ. As used throughout the specification and claims herein, the term "process carried out in a container" means any process, the series of reactions or steps from which they are carried out when substantially using a medium or container. of reaction, as opposed to two or more different or individual reactors.The resulting economy is quite substantial, particularly in a commercial-scale operation.The process of a device of the invention comprises the following steps: (a) placing and causing to react together in a reaction vessel, cyanamide and hydrazine salt of a mineral acid to form the corresponding aminoguanidine salt, (b) generate nitrous oxide in the reaction vessel and effect the diazoation of the aminoguanidine salt to the corresponding guanylylide salt; (c) adding a sufficient proportion of a base to the reaction vessel to obtain a pH of about 4 to about 6.5 and effecting the cyclization of the guanilazide salt to 5-aminotetrazole. According to the most preferred embodiments, the process that is carried out in a container, of the invention begins with the preparation of the hydrazine salt in the same reaction vessel to which the cyanamide is then added, to produce the intermediate of the salt of amipoguanidine. As such, it can be described that the process consists of the following steps: (a) placing and reacting together in an reacdron vessel, hydrazine and a mineral acid to form the corresponding hydrazine salt of the acid; (b) adding an aqueous solution of cyanamide to the reaction vessel and reacting it with the hydrazine salt to form the corresponding aminoguanidine salt; (c) generating nitrous acid in the reaction vessel and efeduing the diazoation of the aminoguanidine salt to the corresponding guanylylide salt; Y (d) adding a sufficient proportion of a base to the reaction vessel to obtain a pH of about 4.2 to about 6.0 and effing the cyclization of the guanilazide salt to 5-aminotetrazole. The following examples are provided to illustrate the invention. In these examples, the main reaction vessel used is a one-liter or three-hundred-milliliter three-necked flask, equipped with a stirrer, a thermometer with a thermocontroller attached thereto, an adapter for retaining a reflux condenser and a funnel. drip that has a lateral arm to admit nitrogen to cover the readivos. Provisions are also made for cooling the flask by means of a water or ice bath and for heating the flask by means of a heating blanket connected to the thermocontroller. All parts and percentages in the examples are in pesos unless otherwise specified.

Example 1 To a one-liter flask, 50.06 g of hydrated hydrazine (content of 64.2% of N2H4) or 1 mol and 85 g of water are charged for dilution. During cooling with ice, 112 g of 32.0% hydrochloric acid (0.98 mol) are added dropwise. When the adidon is consumed, the solution is heated to 85 ° C. 84.5 g of a 50% cyanamide solution are added via a dropping funnel. The first 20% are added quickly. The temperature begins to rise to 90 ° C and is maintained during the adidonal adidon of cyanamide between 85 and 95 ° C. During the addition, which lasts 20 minutes, no external heating was necessary. When, after the addition of cyanamide, the temperature began to fall, heat was applied, the thermostat was set at 85 ° C and heating was prolonged for 2 hours. Titration of a sample of 855.1 mg with 0.1N NaOH between pH 3. 8 and 9.3 consumed 1.35 ml of 0.1002 N NaOH, which indicates a conversion of 94.7%. The pH of the original sample was 7.4, adjusted to 3.8 with a few drops of 0.1 N HCl.

The contents of the roaster are now cooled to 25 ° C and 114 g of 32% HCl (1 mole) are added. While maintaining the temperature between 17 and 22 ° C and shaking vigorously, a solution of 7.12 g of NaNO2 (97% analysis), one mole in 152 g of water is added dropwise. Only one trace of NO was seen. After the addition, the content is maintained at about 20 ° C for 20 minutes. To the readives, 110.2 g of ammonia solution containing 20.32% NH3 (1.32 mol) are rapidly added. The content is heated until reflux begins and is maintained for 2 hours. The pH of the mixture was 5.5-5.6 (measured in small samples diluted 1: 1 with water). The HCI was now added incrementally until the pH was from 4 to 4.1. A total of 38.9 g of HCl (32%) (0.34 moles) were required. After cooling, the 5-ATZ began to crystallize at a temperature of about 54 ° C. The contents were cooled slowly to 10 ° C. By means of an adherent filter, the supernatant solution was removed as much as possible. The filtrate weighed 603 g. To separate the chloride, 240 g of water were added, the contents stirred and briefly heated to 45 ° C, followed by cooling to 10 ° C. The content is transferred to a Buechner funnel and washed three times with approximately equal portions of water, to give 767 g of combined wash water (suspension and washings). The filter retort was dried for 3 hours at 110 ° C to produce 63.9 g of anhydrous 5-ATZ or 74.8%. (Titration analysis 99.8 and 100 2%) Examples 2-8 In these examples the same procedure as in Example 1 is followed, a 300 ml flask is used. The concentration of HCI used from start to finish is 32.23%. The amounts of the reagents, other variables and the results of these examples are summarized in the table below, in which the details are reported in reference to the four reaction stages, that is, stage 1: the hydrazine reaction with hydrochloric acid to form hydrazinium chloride, followed by the reaction of the latter with cyanamide to form the aminoguanidinium chloride, stage 2: the diazoation of the aminoguanidinium chloride to guanylyzide chloride and stage 3: the cyclization of the guanilazide chloride to 5- ATZ TABLE 5-ATZ Synthesis Data Stage 1 Stage 2 No. of N2H4 HCI ai i Grams d 64.20% Example 32.33% 50% Water 32.23% NaN02 Dilution 2 15.20 33.50 32.73 25.55 33.80 21.56 58.80 3 15.20 33.50 25.00 25.55 38.19 21.56 58.80 4 15.10 33.60 21.57 25.50 38.55 21.52 50.14 15.10 33.60 17.45 25.44 33.60 21.49 50.00 6 15.00 33.54 12.40 25.23 33.54 21.30 45.00 7 13.60 33.54 13.60 26.73 33.54 21.40 45.00 8 15.00 33.54 12.40 25.73 33.54 21.30 45.00 Stage 3 Weights v Yields of NH3 to HCI to Water Grams of Grams of% of rindi- Example 20.32% 32.23% Extra Filtration performance 2 29.50 8.77 197.70 18.60 72.00 3 28.00 0.00 82.00 255.90 16.70 64.60 4 28.95 0.00 80.00 236.40 17.26 66.90 26.80 0.00 152.00 222.84 18.53 72.60 6 28.14 6.20 0.00 198.50 17.53 68.90 7 24.00 * 2.00 40.00 Not heavy 7.70 33.50 8 28.14 6.08 80.00 Not weighed 17.53 68.70 * In place of ammonia, 24.00 g of 20.32% sodium hydroxide solution were used.

Example 9 This experiment was carried out in the presence of ethanol to serve as a modifier during the diazoadon stage. Following the procedures described above, the intermediary of aminoguanidine hydrochloride was prepared from 14.93 g of hydrated hydrazine (64.4%, 0.3 moles, diluted with 30 ml of water, 33.4 g of HCI at 31.72%) (0.294 mol) and 25.23 50% cyanamide g (0.3 moles).

To the cooled solution were added 34.09 g of HCI at 31.72% (0.3 moles) and 14 g of ethanol (0.3 moles). A solution of 21.34 g of NaNO2 (0.3 mol) in 50 ml of water is added through the dropping funnel. After the addition, ring closure was carried out by adding 31.4 g of a 22.1% ammonia solution (0.41 moles of ammonia) and refluxing for 2 hours. After adjustment of pH 4 and isolation of 5-ATZ in the usual manner, 17.5 g of anhydrous material are obtained (68.6% yield). The product was free of discoloration.

Example 10 Example 9 was repeated with the same amount of ingredients, but instead of ethanol, 13.9 g of methanol was used. The product consisted of 17.7 g of 5-ATZ (yield of 69.4%), which was white and free from discoloration.

Example 11 This example is provided to demonstrate a stimulation of the continuous reaction, although only one donor was used in the present in place of multiple challengers. However, each stage was carried out for the same duration of time. In this instance, a retention or residence time of 2 hours was arbitrarily selected for each stage.

Simulator 1 Challenger To the one-liter flask was charged 50.06 g of 64.4% hydrazine (1,002 moles) and 85 grams of water. With cooling, a solution of 112 g of 32% hydrochloric acid (0.983 mol) was added. Towards the end of the addition, the temperature was allowed to rise to 40 ° C. After the addition of hydrochloric acid was completed, the ice bath was replaced by a heater attached to a temperature regulator. The dropping funnel was now loaded with 85 g of 50% cyanamide solution (1.01 mol). When the temperature reached 80 ° C, the addition of cyanamide was initiated. After a brief induction period, the temperature rose above the heater reference point and was maintained at about 85-90 ° C. After the addition was completed, the temperature began to fall and was now maintained at 85 ° C for 2 hours. By synchronizing this reaction, it is assumed that the neutralization of hydrazine with hydrochloric acid can be obtained quite easily on a continuous basis in a plant by measuring the components in the correct proportions through the small mixing chamber. Accordingly, the neutralization stage was not timed or synchronized. A larger supply of hydrazine hydrochloride could also be on hand.

Simulator Simulator 2 Readers were cooled to 20 ° C, while 114 g of 32% hydrochloric acid (1 mol) were added. The dropping funnel was charged with a solution of 71.2 g of sodium nitrite (97% analysis, 1 mol) in 150 g of water. The sodium nitrite was added during 1.45 hours, while the temperature was maintained at 20 ± 4 ° C. The sample was maintained for an additional 15 minutes to give a reaction time of 2 hours.

Simulation Challenger 3 To the content of the previous stage, 108 g of ammonia solution, containing 22.1% as NH3 (1.4 moles), were quickly added. The pH was . 7. A complete heating at reflux (104 ° C) was applied for 2 hours. After this time the heat was removed. 46 g of 32% hydrochloric acid (0.4 mole) were added and the solder, now at a pH of 3.9, was allowed to cool slowly. Simulation of the crystallizer or holding tank Large crystals were separated in slow cooling for 1.5 hours. The crystals were filtered in a Buechner funnel. The filtrate weighed 714 g and had a pH of 5.3 after separation of the product. The product was suspended three times with water from the funnel and filtered. The combined wash washings were 503 g. The product was dried at 110 ° C for 3 hours to give 59 7 g of 5-ATZ. The yield of 70%. The product was slightly white.

Example 12 In this example, the amount of sodium nitrite was controlled to ensure the complete reaction of the nitrous acid as it formed and to avoid the presence of free nitrite ions. As shown, the observance of this precaution results in a final 5-ATZ product, which is free from discoloration. The conditions and experimental quantities of the readives used were the same as in Example 10, except that no alcohol was used in the present. During the nitration stage, the free nitrous oxide test was started, when approximately 80% of the sodium nitrite solution had been added. The test involved adding a few drops of potassium iodide / starch solution to a slurry content on a stain plate. At that time the free nitrous acid that was present was released into the test cavity. At the same time, the solution became slightly yellow. Without a waiting period, cyclization was initiated by the addition of ammonia, followed by the usual isolation procedure. The amount of unused sodium nitrite was determined by reweighing the content of the dropping funnel. In this run 0.2 moles of sodium nitrite were consumed. After the usual procedure they were obtained 17. 8 g of clean 5-ATZ (69.8% yield) which was free of discoloration.

Example 13 To the three-necked flask reactor, 15.1 g of 64% hydrazine (0.303 mole) were charged followed by 33.5 g of 32% HCI (0.294 mole). After heating the contents to 85 ° C, 25.5 g of 50% aqueous solution of cyanamide (0.304 moles) was added slowly over a period of about 15 minutes. After the exothermic reaction, the reaction mixture was heated for two hours at 85 ° C. The resulting solution had a pH of 7.4. Titration of a sample at a pH adjusted between 3.7 and 9.2 revealed a conversion of 94.7% to aminoguanidine hydrochloride. An ethyl nitrite generator was established which consisted of a 250 ml Erlenmeyer flask loaded with 21.56 g of sodium nitrite (97% analysis), suspended in 30 ml of water and 15 g of 98% technical grade ethanol. A drip funnel balanced with a stripping gas tube was charged with 15 g of 98% sulfuric acid in 30 ml of water. A Teflon tube was attached to the outlet tube of the drip funnel leading to the main rotor, such that the inlet was below the surface of the aminoguanidine dorhydrate solution. 12.7 g of 32% HCl were poured into the dropping funnel. To verify the pressure and absorption, an oil bubbler tube was attached to the pump. The content of the generator was magnetically stirred on a hot plate in order to maintain the content at about 50 ° C. The sulfuric acid was slowly added to the nitrite for a period of 1.5 hours, to generate a continuous stream of ethyl nitrite. No discoloration was noticed during the nitrosation stage. To effect the cyclization of the guanilazide salt, a 22.1% ammonia solution was added in an increased manner. The pH began to decrease after some heating and after approximately 18. 7 g of ammonia had been added. In total, 38.4 g of the ammonia solution was needed to maintain the pH at 5.5. The boiling point of reflux was found at a temperature of about 90 ° C, due to the ethanol generated from the ethyl nitrite. After one hour of reflux a 32% HCl solution was added in an increased manner to reach and maintain a pH of 4. In the cooling, the hydrated 5-ATZ crystallized as a white product and was filtered. After three washes with water, the filter retort was dehydrated at 110 ° C to produce 19.05 g of anhydrous 5-ATZ at 73.7%, which was white and free of any discoloration.

It is noted that with respect to this date, the best method known to the applicant to carry out said invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following

Claims (10)

1. Claims 1. A process for producing 5-aminotetrazole, which is caraderized because it comprises: (a) reacting an aminoguanidine salt of a mineral acid with a diazoating agent to form the corresponding guanylylide salt, the diazoating agent is selected from the group consisting of: (i) nitrous acid, which is produced in situ by the reaction of a mineral acid with a nitrite salt, the reaction is controlled in such a way as to ensure the consumption of substantially all of the nitrous acid, as it is formed and thereby substantially prevent the presence of free nitrite ions, and (ii) an alkyl nitrite; and (b) cyclizing the guanilazide salt to 5-aminotetrazole.
2. 2. The process according to claim 1, characterized in that the aminoguanidine salt is selected from the group consisting of aminoguanidinium duride, aminoguanidinium bromide and aminoguanidinium nitrate.
3. 3. The process according to claim 2, characterized in that the nitrite salt is an alkali metal nitrite.
4. 4. The process according to claim 3, characterized in that it comprises the additional step of isolating and recovering 5-aminotetrazole.
5. 5. The process according to claim 4, characterized in that the diazoating agent is nitrous acid or an alkyl nitrite.
6. 6. A process for making 5-aminotetrazole, which is caraderized because it comprises: (a) reacting a hydrazine salt of a mineral acid with cyanamide, in an aqueous medium containing free hydrazine to form the corresponding aminoguanidine salt; (b) diazoating the aminoguanidine salt to the corresponding guanilazide salt; and (c) cyclizing the guanilazide salt to 5-aminotetrazole.
7. 7. The process according to claim 6, characterized in that the hydrazine salt is prepared by reacting a mineral acid with hydrazine, using at least about one mole of hydrazine per mole of acid.
8. 8. The process according to claim 7, characterized in that the mineral acid is selected from the group consisting of hydrochloric, hydrobromic and nitric acid.
9. 9. The process according to claim 6, characterized in that the preparation of the aminoguanidine salt in step (a) is effected at a temperature of about 70 to about 90 ° C, the diazoadd reaction of step (b) is effected at a temperature of about 8 to about 30 ° C and step (c) is effected at a temperature of about 80 to about 110 ° C and a pH of about 4.4 to about 5.8.
10. 10. A process that is carried out in a retort, for the production of 5-aminotetrazole, caraderized because it comprises: (a) placing and reacting together in a reaction vessel, hydrazine and a mineral acid to form the corresponding hydrazine salt; (b) adding cyanamide to the reaction vessel and reacting it in an aqueous medium with the hydrazine salt to form the corresponding aminoguanidine salt; (c) adding nitrous oxide to the reaction vessel and ephedra the diazoadon of the aminoguanidine salt to the corresponding guanylylide salt; Y (d) adding a sufficient proportion of a base to the reaction vessel to obtain a pH of the reaction mixture of about 4 to about 6.5 and cyclizing the guanylylide salt to 5-aminotetrazole.