US5594146A - Process for producing 5-aminotetrazole
Sep. 23, 2024
USA - Process for producing 5-aminotetrazole
1. Field of the Invention
The present invention relates to a process for commercially producing 5-aminotetrazole suitable for use as an intermediate in the production of gas generants, medicines or pesticides. More specifically, it relates to a process for producing 5-aminotetrazole from cyanamide and hydrazine. The present invention also relates to a method for powdering the 5-aminotetrazole or a metal salt thereof by spray drying.
2. Description of the Related Art
Several processes for producing 5-aminotetrazole are already known in the art. For example, Journal of Organic Chemistry, 15, () proposes a process for producing 5-aminotetrazole by reacting cyanamide with hydrazoic acid to obtain imidoazide, followed by cyclization or ring formation thereof. This reaction is considered to proceed as follows. ##STR1##
In addition, Journal of Organic Chemistry, 18, 779 () proposes a process for producing 5-substituted tetrazole by reacting a salt of aminoguanidine with nitrite to form a salt of diazoguanidine, followed by cyclization thereof with sodium acetate, sodium carbonate or diluted mineral acid upon heating, as follows. Furthermore, Czechoslovakia Patent No. (patented Sep. 15, ) proposes a process for producing 5-aminotetrazole by reacting aminoguanidine sulfate with nitrite in HCl to form diazoguanidinium chloride, followed by cyclization with sodium acetate upon heating. ##STR2## wherein X represents I, HSO4 or Cl.
However, since the hydrazoic acid, which is explosive and deadly poisonous, must handle as a starting material in the form of a free acid in the above-mentioned first proposal, special attentions should be paid to materials and sealability of apparatuses, and facilities for treating exhaust gas and waste water, and therefore, this proposal was difficult to be practically used as an industrial scale.
Even in the above-mentioned second proposal, it is necessary to use an expensive salt of aminoguanidine as a starting material. Furthermore, a salt of diazoguanidine, which should be isolated as an intermedial product, is an unstable compound, and therefore, a portion thereof is decomposed to decrease the yield and also the use of the special materials for the apparatuses or the special facilities for the treatment apparatuses etc. Thus, again, this proposal is difficult to be practiced at an industrial scale and is not economical.
On the other hand, the materials capable of forming a salt with a reaction of 5-aminotetrazole include mineral acids, alkali metals, alkaline earth metals, and transition metals. Typical examples of the mineral acids are hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc. The alkali metals and alkaline earth metals are mainly used as the hydroxides or oxides for the reaction, typically in the form of sodium hydroxide, potassium hydroxide, magnesium oxide, etc. Typical examples of the transition metals are nickel, zinc, copper, molybdenum, iron, etc. These transition metals are not usually used in the form of the metal per se, but used as the inorganic metal salts or organic metal salts. Examples of the inorganic metal salts are copper chloride and molybdenum chloride, etc. and examples of the organic metal salts are nickel acetate and zinc acetate.
Especially many metal salts of 5-aminotetrazole have high solubilities in water and the other organic solvents. Accordingly, when anhydrous or water-free salts of 5-aminotetrazole are intended to obtain by concentrating the solution containing the above-mentioned metal salts of 5-aminotetrazole, followed by crystallizing, separating and drying the resultant crystals. However, since the solubilities thereof in the solvent are high, there are many cases that the yield of the desired anhydrous salt during the separation step of the crystalline is low and the filtering properties are poor. Furthermore, due to the inherent properties of the materials there are many cases where the hydration is easy to occur. Thus, the drying step thereafter should be sufficiently effected. As mentioned above, the steps of the prior art processes are totally troublesome, and therefore, there are needs that the desired anhydride products can be easily obtained by simply separating and drying the resultant products.
It is considered that the reaction mixture containing the desired metal salts of 5-aminotetrazole is dispersed and crystallized in an organic solvent. However, the use of organic solvents is not preferable from the viewpoints of operation as well as safety and sanitation. In addition, when the organic solvent is recovered, since the new process step is added for this purpose, the production cost is increased.
Azide based conventional gas generants using, for example, sodium azide as a fuel have the problem of the toxicity of the unreacted azide remained. In addition, in the conventional gas generation apparatus, the reaction products formed simultaneously with the generation of gas should be efficiently filtered with a filter.
On the other hand, since conventional non-azide based gas generants are intended to utilize due to their low toxicity, there are disadvantages that the combustion temperature becomes higher, when compared with the case of the azide-based gas generants, and therefore, the combustion temperature is higher than the melting point of the remaining reaction products are difficult to separate by a filter. Therefore, it is intended to modify the form of the reaction products by the addition of an appropriate additive such that the filtration can be effected. It is believed that, to obtain the particles of the reaction product capable of being easily filtered, a high melting point component and an appropriate low boiling point component are coexisted and the high melting point component is fusion coagulated with the low boiling point to thereby form the particles.
The alkali metal salts of 5-aminotetrazole can be a nitrogen gas generating source as a fuel and also can form an appropriate low boiling point component by the reaction with other additives such as silicates or carbonates. Furthermore, the alkali metal salts of 5-aminotetrazole has an effect that the amount of nitrogen oxides (NOx) generated during the decomposition can be reduced.
SUMMARY OF THE INVENTIONAccordingly, the objects of the present invention are to eliminate the above-mentioned problems of the prior art and to provide a process for commercially producing 5-aminotetrazole with safety at a cheaper cost.
Another object of the present invention is to provide a process for producing an anhydrous (or water-free) 5-aminotetrazole (or a metal salt thereof) at a high yield in the form of powder (or particles) which are capable of being easily handled.
Other objects and advantages of the present invention will be apparent from the following description.
In accordance with the present invention, there is provided a process for producing 5-aminotetrazole comprising the steps of:
(a) reacting cyanamide with hydrazine in a solvent to form a salt of aminoguanidine;
(b) adding thereto an acid and then a nitrite to form a salt of diazoguanidine; and
(c) cyclizing the salt of diazoguanidine, upon heating, to thereby produce the 5-aminotetrazole, without isolating the intermediate product.
In accordance with the present invention, there is also provided a process for producing 5-aminotetrazole in the form of powder (or particles) comprising spray drying a solution of the 5-aminotetrazole obtained above or a metal salt thereof. Especially, the water-soluble metal salts (e.g., potassium salt, magnesium salt, etc.) can be suitably powdered according to this process.
BRIEF DESCRIPTION OF THE DRAWINGSThe present invention will be better understood from the description set forth below with reference to the accompanying drawings, wherein:
FIG. 1 is an IR spectrum of the desired compound, i.e., 5-aminotetrazole hydrate, obtained by the process according to the present invention;
FIG. 2 is an IR spectrum of the desired compound, i.e., anhydrous 5-aminotetrazole, obtained by the process according to the present invention;
FIG. 3 is an IR spectrum of the desired compound, i.e., the potassium salt of 5-aminotetrazole, obtained by the process according to the present invention; and
FIG. 4 is an IR spectrum of the desired compound, i.e., the magnesium salt of 5-aminotetrazole, obtained by the process according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTSThe present invention will now be described in more detail.
According to the present invention, the desired 5-aminotetrazole and the salts thereof can be easily produced, with safety, by forming aminoguanidine from cyanamide and hydrazine, then forming a salt of diazoguanidine by the reaction with nitrite, followed by cyclizing or ring forming, without isolating the salt of diazoguanidine.
The reaction schemes according to the present invention can be summarized as follows. ##STR3## wherein X represents Cl, HSO4, NO3, H2 PO4, etc.
According to the present invention, cyanamide is first allowed to react with hydrazine in an appropriate solvent (e.g., water, ethanol, isopropanol, etc.) to form a solution of a salt of aminoguanidine. This reaction an acid is added to the hydrazine or hydrazine hydrate in the solvent to thereby adjust the pH of the solution to prepare the solution or slurry of a salt of hydrazine. It is preferable in this reaction that about 0.5 to 3 equivalent, more preferably about 0.8 to 1.2 equivalent, based upon 1 mole of the hydrazine hydrate. Alternatively, the solution of a salt of hydrazine can be prepared by dissolving the salt of hydrazine in an appropriate solvent.
The acids usable for neutralizing the hydrazine hydrate are not specifically limited and preferably include, for example, hydrochloric acid, sulfuric acid, nitric acid, carboxylic acid, and phosphoric acid. From the economical viewpoints, the use of hydrochloric acid or sulfuric acid is most preferable. Examples of the salts of hydrazine usable in the present invention are hydrochloride, sulfate, nitrate and carbonate. From the economical viewpoints, the use of hydrochloride and sulfate is most preferable.
In the present invention, the cyanamide preferable in an amount of about 0.8 to 3 mole, more preferably 0.8 to 1.5 mole, based upon 1 mole of hydrazine, is added to the above-mentioned solution of the salt of hydrazine, followed by heating to form a solution of a salt of aminoguanidine.
The cyanamide to be used in the present reaction can be added either in the form of a crystalline or a solution. When the cyanamide is added in the form of a solution, any solvent which does not react with the starting materials and the reaction intermediates and which is capable of dissolving the starting materials can be used without any limitation. Among such solvents, the use of water is most preferable from the viewpoints of the cheap cost and the high safety. The preferable concentration of cyanamide is about 5 to 100% by weight, more preferably 10 to 60% by weight.
Although there are no specific limitations to the reaction temperature and the reaction time, the reaction temperature is preferably 15° C. or more, more preferably 50° to 95° C. from the viewpoints of the preferable reaction speed and the suppression of the decomposition of the starting material and the formed aminoguanidine and the suppression of the side reactions. The preferable reaction time is about 30 minutes to 8 hours, more preferably 2 to 5 hours.
To the solution of the salt of aminoguanidine obtained in the above reaction, an acid is added and then a nitrite solution is added to allow the reaction therebetween. As a result, a solution of a salt of diazoguanidine is formed, the acids usable in this reaction include, for example, hydrochloric acid, sulfuric acid, nitric acid or other inorganic acids. The use of hydrochloric acid is most preferable from the viewpoints of the reactivity.
There are no specific limitation to the amount of the acid to be used, the preferable amount of the acid is 0.5 to 3 equivalent, more preferably 0.8 to 1.2 equivalent based upon 1 mole of the salt of aminoguanidine.
The nitrites usable in the present invention preferably include sodium nitrite, potassium nitrite, calcium nitrite, ammonium nitrite. From the viewpoints of the reactivity, the use of alkali metal salts of nitrite is preferable and from the viewpoints of solubility and also from the economical viewpoints, the use of sodium nitrite is further preferable. Although there are no specific limitations to the amount of the nitrate, the use of the nitrate in an amount of 0.5 to 3.0 equivalent, more preferably 0.8 to 1.2 equivalent, based upon 1 mole of the salt of aminoguanidine is preferable.
The nitrites are preferably added to the reaction mixture in the form of a solution in the same solvent as used in the previous step or in a solvent missible with the solvent used in the previous step. The preferable concentration of the nitrite in the solution is 5 to 100% by weight.
The reaction is preferably carried out at a reaction temperature of 50° C. or less, more preferably 0° C. to 40° C, from the viewpoints of the reaction velocity. The preferable reaction time is 5 minutes to 5 hours, although this is not critical.
According to the present invention, a pH of the above-prepared reaction solution is preferably adjusted to 1 to 9, more preferably 1 to 3, with the addition of an alkaline solution to the reaction solution. Thereafter the reaction mixture is heated to thereby effect the desired cyclization (or ring forming). Thus, the desired 5-aminotetrazole hydride can be produced in the form of a crystal. The above-mentioned cyclization reaction can be preferably carried out at a pH of 1 to 9, more preferably 1 to 3.
The alkalis usable for the pH adjustment are not specifically limited, but preferably include inorganic alkali such as sodium hydroxide, potassium hydroxide, calcium hydroxide. Although various solvents can be used, the use of an aqueous sodium hydroxide solution is preferable from the viewpoints of the easy reactivity and availability.
The reaction is preferably carried out, while vigorously stirring, by adding an alkaline solution in a concentration of, for example, 5 to 100% by weight in such a rate that the reaction temperature of, preferably, 40°-100° C., more preferably 70°-95° C., can be maintained during the reaction.
Although there are no specific limitations to the reaction time of the cyclization, the reaction time is preferably 15 minutes to 6 hours, more preferably 1 to 3 hours.
After the completion of the reaction, the reaction mixture is preferably gradually cooled to a temperature of, for example, 5° C. or less, to precipitate the desired 5-aminotetrazole hydrate in the crystalline form. The yield of the crystal is usually 70% or more, based upon the starting hydrazine, and the purity is usually 95% or more, determined by a neutralization titration.
Thus, the desired 5-aminotetrazole according to the present invention is obtained in the form of hydrate. If desired, the 5-aminotetrazole having a high purity can be obtained by purifying the above product using, for example, column chromatography, or recrystallization.
The recrystallization can be carried out by using a polar solvent such as water, an alcohol (e.g., methanol, ethanol, isopropanol, n-propanol, etc.), dimethylformamide (DMF), but the use of water is preferable from the viewpoints of the solubility and also from the economical viewpoints. For example, the crystals of 5-aminotetrazole hydrate obtained in the above-mentioned reaction according to the present invention is dissolved, upon heating, in 0.5 to 6 times by weight of a solvent, followed by cooling to crystallize the desired product. The crystallized product is recovered by filtration. The resultant wet crystals are dried under reduced pressure at a temperature of, for example, 30° C. or less, more preferably 20° C. or less, to give the desired 5-aminotetrazole hydrate having a purity of 98% or more in the crystalline form.
The hydrate crystals obtained above can be converted to the anhydrous (or water-free) form by drying a conventional dryer such as a box-type dryer, a fluidized dryer, a flash dryer. Especially, when the anhydrous alkali metal salts (e.g., potassium salt) of 5-aminotetrazole having a large solubility to water is desired to produce, the reaction solution obtained by the reaction in an aqueous solution can be advantageously directly spray dried. This is also preferable from the viewpoints of the yield and simplification of the process steps.
The drying conditions depend upon the type of the dryer to be used. When a box-type dryer is used, the use of the drying temperature of 60° to 200° C., more preferably 80° to 150° C. and the drying time of 30 minutes to 48 hours, more preferably 8 to 16 hours is preferable from the viewpoints of the dewatering velocity and the prevention of decomposition of anhydrous 5-aminotetrazole.
When anhydrous metal salts, especially alkali metal or alkaline earth metal salts are intended to produce, the desired anhydrous product can be directly obtained from the reaction solution by spray drying the uniform solution obtained by neutralizing the 5-aminotetrazole with an equivalent amount of a metal hydroxide or oxide. Thus, the conventional steps for obtaining the anhydrous product by the concentration, separation and drying can be omitted.
In the case of the spray drying, the hot air temperature is set to a temperature higher than those of 10 the conventional box-type dryer, fluidized dryer, and flash dryer, to effect the vaporization of a solvent. Typically, the use of the hot air temperature of 120° to 230° C., more preferably 180° to 215° C. is preferable, provided that the temperature should be not more than the decomposition temperature of the anhydrous product to be dried. The dried product thus obtained is in the form of power, of which specific surface area is larger by several times or more than that obtained by, for example, box drying.
EXAMPLESThe present invention will now be further illustrated by, but is by no means limited to, the following Examples.
Example 1To a ml four necked flask provided with a thermometer and an agitating means, 65.0 g (1.3 mole) of hydrazine-monohydrate was charged. While agitating, 131.8 g (1.3 mole) of 36% by weight aqueous hydrochloric acid was added to neutralize and, then, 109.2 g (1.3 mole) of 50% by weight aqueous cyanamide solution and 185 g of water were dropwise added, followed by reacting at 85° C. for 3 hours. After completion of the reaction, 121.6 g of 36% by weight aqueous hydrochloric acid was added to the reaction mixture and at a reaction temperature of 40° C. or less, 321.7 g (1.2 mole) of 26% by weight aqueous sodium nitrite solution was dropwise added. After allowing to stand at room temperature over night, 48.5 g (1.2 mole) of 99% sodium hydroxide was added to allow the reaction mixture to react at a reaction temperature of 85° C. for 3 hours. After completion of the reaction, the reaction mixture was cooled to 3° C. The reaction mixture separated by suction filtration to obtain 124.0 g of 5-aminotetrazole in the crystalline form.
To the crystalline 5-aminotetrazole obtained above, 372.0 g of water was added, followed by heating until 85° C. to effect the dissolution. The solution was then cooled to 3° C. Thus, by suction filtration, 103.8 g of 5-aminotetrazole hydrate in the wet crystalline form. The wet crystal thus obtained was dried under reduced pressure at room temperature for one hour. Thus, 97.7 g (yield 72.9%) of 5-aminotetrazole (i.e., "AT") monohydrate in the crystalline form having a purity of 99.9% was obtained. The resultant purified 5-aminotetrazole hydrate had a melting temperature of 207°-209° C. and it was observed by a thermogravimetric analysis that the weight corresponding to the monohydrate was decreased before the melting. The result of an IR analysis is shown in FIG. 1 and is the same as that of the standard sample.
A 5.12 g amount of the 5-aminotetrazole hydrate obtained above was spread in a dryer and was heated at 110° C. for 12 hours to remove the water of crystallization. Thus, 4.21 g of the anhydrous 5-aminotetrazole having a purity of 100.0% (yield=99.6% based upon 5-aminotetrazole hydrate). The melting temperature of the resultant anhydrous 5-aminotetrazole was 207°-209° C. and the result of an IR analysis is shown in FIG. 2 and is the same as that of the standard sample.
Example 2sulfate and 25 g of water were charged and 84.0 g of 50% aqueous cyanamide solution was dropwise added, followed by reacting at 85° C. for 3 hours. After completion of the reaction, 127.3 g (0.5 mole) of 35% sulfuric acid was added and, in the similar manner as in Example 1, 73.3 g (0.71 mole) of 5-aminotetrazole hydrate in the crystalline form was obtained (yield=71.2% based upon hydrazine sulfate). The resultant 5-aminotetrazole hydrate had a melting temperature of 207°-209° C. and the decrease in the weight corresponding to the weight of the monohydrate was observed before the melting by a thermogravimetric analysis. Furthermore, the result of an IR analysis is the same as that of FIG. 1 and is the same as that of the standard sample.
Example 3Example 1 was repeated, except that crystalline cyanamide (purity=98%) was used instead of 50% aqueous cyanamide solution. As a result, 97.1 g (0.94 mole) of 5-aminotetrazole hydrate in the crystalline form was obtained (yield=72.3% based upon hydrazine sulfate). The resultant 5-aminotetrazole hydrate had a melting temperature of 207°-209° C. and the decrease in the weight corresponding to the weight of the monohydrate was observed before the melting by a thermogravimetric analysis. Furthermore, the result of an IR analysis is the same as that of FIG. 1 and is the same as that of the standard sample.
Example 4To a 100 liter solution vessel provided with a thermometer and an agitating means, 51.045 kg of distilled water was charged. While agitating, 0.515 kg (6.00 mole) of 5-aminotetrazole in the form of powder was dissolved. Thus, 51.560 kg of 1% by weight aqueous 5-aminotetrazole solution was obtained.
The aqueous solution obtained above was charged, by a continuous flow pump, to a spray dryer (i.e., OUT-12 available from Ohkawara Kakohki K. K., Japan). The pressurized nozzle was used as a spray nozzle. The apparatus was composed of a drying chamber and cyclone and finely divided powder was collected in a stainless steel collection bottle provided at the bottom of the drying chamber and cyclone.
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The hot air temperature of the spray dryer was set to 215° C. After the hot air temperature reached the setting temperature, the above aqueous solution was introduced to the spray dryer at a flow rate of 15 liter/hr. It was confirmed from the observation window that the dry crystal was obtained immediately after the introduction.
After completion of the introduction of the aqueous solution, a heater for the hot air was turned off. After allowing the apparatus to cool, the sample was collected. The powder sample obtained from the sample collection bottle and the drying chamber was 0.390 kg. The water content of the sample thus obtained was 0.10% by weight, determined by a Karl Fisher method. Thus, it was confirmed that the anhydrous product was obtained. The yield from the aqueous solution was thus 75%. Furthermore, according to a scanning type electro micrograph, it was confirmed that the resultant powdery crystals were substantially spheric and granular type particles. The particle size distribution was determined by a laser diffraction type particle size distribution meter (i.e., Microtrac FRA available from Leed's & Northrup Co., U.S.A.). When the particle size distribution was determined using n-heptane as a dispersion medium, the cumulative 10% diameter was 12 μm, the cumulative 50% diameter was 27 μm, the cumulative 90% diameter was 49 μm and the average diameter was 30 μm, all based upon the volume diameter.
After spray drying test, the drying chamber was washed with about 6 liters of water and the washed solution was concentrated and dried to solid. The resultant solid was 0.258 kg, which contained 99.8% by weight of 5-aminotetrazole and 0.2% by weight of water, as a result of the analysis. Thus, the resultant solid was the anhydrous product. This anhydrous product corresponded to 20% by weight of the starting material dissolved in the distilled water and the recovered anhydrous product has the sufficient quality to be commercially used.
Example 5To a ml four necked flask provided with a thermometer and an agitating means, 482.4 g (3.00 mole) of 35% by weight aqueous potassium hydroxide solution was charged and heated to 80° C. While agitating, 257.8 g (3.00 mole) of 5-aminotetrazole in the form of powder was added. Thus, 739.0 g of 50% by weight aqueous potassium salt of 5-aminotetrazole solution was obtained, after reacting for 30 minutes.
The aqueous solution obtained above was charged, by a continuous flow pump, to a spray dryer (i.e., Mobile Minor available from Niro Co., Denmark). The rotary disc nozzle was used as a spray nozzle. The apparatus was composed of a drying chamber and cyclone and finely divided powder was collected in a stainless steel collection bottle provided at the bottom of the cyclone.
The hot air temperature of the spray dryer was set to 200° C. After the hot air temperature reached the setting temperature, the above aqueous solution was introduced to the spray dryer at a flow rate of 600 ml/hr. It was confirmed from the observation window that the dry crystal was obtained immediately after the introduction.
After completion of the introduction of the aqueous solution, a heater for the hot air was turned off. After allowing the apparatus to cool, the sample was collected. The powder sample obtained from the sample collection bottle and the drying chamber was 277.1 g. The water content of the sample thus obtained was 0.03% by weight, determined by a Karl Fisher method. Thus, it was confirmed that the anhydrous product was obtained. The yield from the aqueous solution was thus 75%. Furthermore, according to a scanning type electro micrograph, it was confirmed that about 50% of the resultant powdery crystals were substantially spheric type particles. The particle size distribution was determined by a laser diffraction type particle size distribution meter (i.e., Microtrac FRA available from Leed's & Northrup Co., U.S.A.). When the particle size distribution was determined using n-heptane as a dispersion medium, the cumulative 10% diameter was 7 μm, the cumulative 50% diameter was 26 μm, the cumulative 90% diameter was 46 μm and the average diameter was 27 μm, all based upon the volume diameter.
After spray drying test, the drying chamber was washed with about 3 liters of water and the washed solution was concentrated and dried to solid. The resultant solid was 74.0 g, which contained 99.8% by weight of potassium salt of 5-aminotetrazole and 0.2% by weight of water, as a result of the analysis. Thus, the resultant solid was the anhydrous product. This anhydrous product corresponded to 20% by weight of the starting potassium salt and the recovered anhydrous product has the sufficient quality to be commercially used. Futhermore, the result of an IR analysis is shown in FIG. 3 and is the same as that of the standard sample.
Example 6To a ml four necked flask provided with a thermometer and an agitating means, 76.5 g (0.90 mole) of 5-aminotetrazole and g of water was charged and heated to 80° C. Thereafter, 363.2 g (0.45 mole) of 5% by weight of magnesium oxide slurry was dropwise added, followed by allowing to react for one hour. While agitating, thus .0 g of 6% by weight aqueous magnesium salt of 5-aminotetrazole solution was obtained.
The aqueous solution obtained above was charged, to a spray dryer in the same manner as in Example 4, except that the sample solution to be introduced was different. The spray drying conditions were the same as in Example 4. It was confirmed from the observation window that the dry crystal was obtained immediately after the introduction.
After completion of the introduction of the aqueous solution, a heater for the hot air was turned off. After allowing the apparatus to cool, the sample was collected. The powder sample obtained from the sample collection bottle and the drying chamber was 65.0 g. The water content of the sample thus obtained was 0.10% by weight, determined by a Karl Fisher method. Thus, it was confirmed that the anhydrous product was obtained. The yield from the aqueous solution was thus 75%. Furthermore, according to a scanning type electro micrograph, it was confirmed that the substantial amount of the resultant powdery crystals were nearly spheric type particles. The particle size distribution was determined in the same manner as in Example 4. When the particle size distribution was determined in the same manner as in Example 4, the cumulative 10% diameter was 6 μm, the cumulative 50% diameter was 18 μm, the cumulative 90% diameter was 44 μm and the average diameter was 30 μm, all based upon the volume diameter.
After spray drying test, the drying chamber was washed with about 3 liters of water and the washed solution was concentrated and dried to solid. The resultant solid was 17.3 g, which contained 99.8% by weight of magnesium salt of 5-aminotetrazole and 0.2% by weight of water, as a result of the analysis. Thus, the resultant solid was the anhydrous product. This anhydrous product corresponded to 20% by weight of the starting magnesium salt and the recovered anhydrous product has the sufficient quality to be commercially used. Furthermore, the result of an IR analysis is shown in FIG. 4 and is the same as that of the standard sample.
Comparative Example 1To a ml four necked flask provided with a thermometer and an agitating means, 103.0 g (1.20 mole) of 5-aminotetrazole and 300.0 g of methanol were charged. 5-aminotetrazole and 300.0 g of methanol were charged. While agitating, 379.2 g (0.60 mole) of 21% by weight solution of potassium hydroxide in methanol was dropwise added, followed by allowing to react at 25° C. for 30 minutes. After completion of the reaction, the reaction mixture was concentrated at a temperature of 67° C. After distilling off 301 g of μmethanol, the reaction mixture was cooled to 20° C. and the reaction mixture was separated by a suction filtration. Thus, 112.2 g of the wet crystal was obtained. The wet crystal thus obtained was dried at 80° C. for 12 hours to obtain 100.1 g (yield=67.3%) of potassium salt of 5-aminotetrazole in the crystalline form having a purity of 99.5%. The resultant purified potassium salt of 5-aminotetrazole had a melting temperature of 267°-269° C. The result of the quantitative determination of potassium according to an inductive coupling type plasma analysis (ICP) was 31.3%, which substantially corresponds to the potassium content of a 1:1 composition of 5-aminotetrazole and potassium.
Comparative Example 2To a ml four necked flask provided with a thermometer and an agitating means, 76.5 g (0.90 mole) of 5-aminotetrazole and 450.0 g of water were charged. While agitating, 360.0 g (0.90 mole) of 16.5% by weight aqueous potassium hydroxide solution was dropwise added, followed by allowing to react at 25° C. for 30 minutes. After completion of the reaction, the resultant reaction mixture was concentrated in an evaporator. After 752.3 g of water was distilled off, the resultant mixture was cooled to 20° C. The suction filtration was tried to separate the solid product, but the filtering properties were very poor. Therefore, the concentration was continued to effect in the evaporator. Finally, the mixture was solid dried. The crystals adhered to the walls of the evaporator vessel were seratched off and powdered to obtain 129.0 g of the wet crystals. The wet (yield 96.2%) of the potassium salt of 5-aminotetrazole in the crystalline form having a purity of 99.2%.
The physical properties of the products obtained in Examples 1, 4-6 and Comparative Example 1 are shown in Table 1. The determination methods are as follows.
Heat of Decomposition
According to a JIS (Japan Industrial Standards) M method "Coals and Cokes-Method for Determining Heat of Calorific Power" determined by Nenban-shiki Type B calorimeter
Decomposition Initiatinq Temperature
The exothermic initiating temperature of a differential scanning calorimeter
Combustion Test
1. A test sample was prepared by mixing 30 parts by weight of a sample to be tested with 70 parts by weight of an oxygen source (i.e., potassium nitrate).
2. The test sample was formed to a shape having a length of 250 mm, a width of 20 mm and a height of 10 mm, based upon a test method for a flammable solid (4.1) in the so-called "Orange Book".
3. One edge of the test sample was heated by a gas burner and the combustion conditions and the exposure conditions were observed.
The results are shown in the following Table 1.
TABLE 1
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Particle size
distribution/Microtrac FRA
Specific Decom-
Shape of (μm) surface
Heat of
position
cyrstal- 10% 50% 90% area/
decompo-
initiat-
Drying
line Purity
diam-
diam-
diam-
Average
BET sition
ing
Combustion
No. Sample
method
(SEM)
(%) eter
eter
eter
diameter
(m.sup.2 /g)
(cal/g)
(°C.)
test
__________________________________________________________________________
Example
anhydrous
Crystalli-
Needle
99.2
55.6
199.7
472.5
238.2
0.12 219 Decompo-
1 5AT zation sition
Box No
drying exposure
Example
anhydrous
Spray
Powder
98.8
12.2
27.4
49.0
29.9 0.70 218 Decompo-
4 5AT drying
particle sition
No
exposure
Comp.
5AT K salt
Crystal-
Rectan-
99.5
56.2
110.3
193.4
119.8
0.09 315 Decompo-
Ex. 1 line Box
gular sition
drying after
melting
No
exposure
Example
5AT K salt
Spray
Nearly
98.2
7.1 25.8
46.2
27.0 0.68 313 Decompo-
5 drying
sphere sition
after
melting
No
exposure
Example
5AT Mg
Spray
Nearly
98.4
6.4 18.0
43.6
30.0 0.72 220 Decompo-
6 salt drying
sphere sition
after
melting
No
exposure
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As is clear from the above explanation, the present process relates to a production of 5-aminotetrazole, without isolating the intermediate, at a high yield, which is conventionally produced by the steps of isolating and purifying the intermediates, i.e., aminoguanidine and salts of diazoguanidine from cyanamide and hydrazine.
According to the present process, the various problems passesed by the known processes, e.g., danger of the intermediates and the increase in the production cost caused therefrom and insufficient yield, can be solved and the desired compounds, 5-aminotetrazole hydrate and anhydrous 5-aminotetrazole can be produced with safety and less expensive costs in a commercial scale.
Furthermore, according to the present invention, finely divided alkali metal salts of 5-aminotetrazole, which is capable of uniformly mixing and dispersing with fuels, oxidants and additives, can be advantageously by using a spray drying as a drying method.
Tetrazolium Compounds: Synthesis and Applications in ...
Tetrazoles represent a class of five-membered heterocyclic compounds with polynitrogen electron-rich planar structural features. This special structure makes tetrazole derivatives useful drugs, explosives, and other functional materials with a wide range of applications in many fields of medicine, agriculture, material science, etc. Based on our research works on azoles and other references in recent years, this review covers reported work on the synthesis and biological activities of tetrazole derivatives.
Like other azole compounds, due to the relatively late start of the synthesis and study of tetrazole compounds, they did not attracted much attention in the beginning. Since , when Bladin first synthesized tetrazole derivatives (2-cyanophoric-5-phenyltetrazole) to , only some 300 kinds of derivatives were reported [ 2 ]. Since the s, when tetrazole compounds became widely used in agriculture, biochemistry, medicine, pharmacology, explosives and other aspects, research began to develop rapidly [ 3 , 4 ]. The tetrazolyl functional group which was often considered as a carboxylic acid replacement in drugs, not only because the pKa is close, but it also has approximately the same planar delocalized system space requirements, and it provided a maximum nitrogen content of any heterocyclic compound [ 5 ]. The planar ring skeleton structure and the nitrogen-rich multi-electron conjugated system confer tetrazole derivatives with both donor and acceptor electronic properties. Tetrazole and its derivatives have this attracted the interest of scientists because of their unique structures and their potential applications as antihypertensive, anti-allergic, antibiotic and anticonvulsant agents [ 6 , 7 , 8 , 9 ]. In the present review, emphasis was focused on the diverse pharmacological properties associated with substituted tetrazoles in the past few years and a conclusive discussion on structure-activity relationship (SAR) of these compounds is provided.
Tetrazole is a heterocyclic compound containing a carbon atom and four nitrogen atoms in a five-membered ring. Theoretically there are three precursor tetrazole isomers: i.e., 1H-tetrazole ( 1 ), 2H-tetrazolium ( 2 ) and 5H-tetrazole ( 3 ) ( ). Substituted tetrazoles exist as a nearly 1:1 ratio of 1H- and 2H-tautomeric forms. Previous studies had shown that the two positional isomers 1 and 2 may be differentiated on the nuclear magnetic resonance (NMR) timescale [ 1 ].
When the hydrazides 17 were treated with thionyl chloride, the corresponding hydrazidoyl compounds 18 were obtained ( Scheme 5 ). Next the reaction of compounds 18 with phenylhdyrazine was examined to prepare the hydrazidines 19 which can be oxidized to formazan derivatives 20 . 2,5-Disubstituted tetrazoles 21 can be synthesized by reacting compounds 20 with potassium carbonate [ 38 ]. Compounds 20 also can be synthesized from compounds 22 [ 39 ].
There are some ways to get 2,5-disubstituted-tetrazoles. One of the most efficient routes ( Scheme 4 ) uses lithium trimethylsilyldiazomethane ( 15 ) prepared from TMSCHN 2 and lithium diisopropylamide (LDA), which reacts smoothly with the methyl esters of carboxylic acids at 0 °C to give compounds 16 in good yields [ 37 ].
If one wants to prepare 1,5-disubstituted-tetrazoles from the corresponding amide, there are many routes ( Scheme 3 ). First, one can prepare an oxyphosphonium salt under Mitsunobu conditions from the corresponding amide, followed with reaction with trimethylsilyl azide leading to the desired 1,5-disubstituted-tetrazoles. This method proves to be especially useful for applications when an N-protected tetrazole is required. Preservation of chirality in the synthesis of a tetrazole analogue of an amino acid (phenylalanine) was demonstrated [ 29 ]. In addition to the above direct approach, we can also through multiple steps to generate 1,5-disubstituted tetrazoles. Usually compounds 9 can be converted to compounds 10 with phosphorus oxychloride (POCl 3 ) and thionylchloride (SOCl 2 ) [ 30 ]. Compounds 11 can also be prepared in suitable yields by reaction of compounds 9 with Lawesson&#;s reagent or phosphorus pentoxide [ 31 ]. 1,5-Disubstituted tetrazoles can also be synthesized by reacting compounds 10 with triethyl orthoformate and sodium azide [ 32 ]. Compounds 12 can be synthesized by the reaction of compounds 10 and compounds 11 with hydrazine hydrate [ 33 , 34 ]. 1,5-Disubstituted tetrazoles can finally be synthesized by reacting 12 with CH 3 COOH and aqueous NaNO 2 under ice-bath conditions, making sure that the reaction temperature is below 5 °C [ 35 , 36 ].
The [3+2] cycloaddition between hydrazoic acid and cyanide derivatives is well known as an efficient route ( Scheme 2 ). We can thus get substituted tetrazoles 5 from isocyanides 6 . The reaction of 6 and azidotrimethylsilane (1.5 equiv.) was conducted in MeOH (0.5 M) in the presence of a catalytic amount of HCl (2 mol %, 1.0 M in Et 2 O solution) at 60 °C [ 13 , 14 ]. One of the main procedures frequently used for the preparation of 5-substituted tetrazoles 7 involves heating a suspension of 6 , sodium azide, ammonium chloride and lithium chloride (1.20 g, 28 mmol) in anhydrous dimethylformamide (DMF) under stirring at 110 °C [ 15 , 16 , 17 ]. Compound 7 was also obtained in a sealed pressure vessel reaction where NaN 3 dissolved in H 2 O, compound 6 , ammonium chloride, ammonium fluoride and propane-1,2-diol (DPOL) were stirred and heated for 48 h [ 18 ]. Aryloxy tetrazoles were commonly prepared by the reaction of phenols with cyanogen bromide in the first step. Then sodium azide was added into refluxing acetone-water [ 19 ]. The most convenient route to 5-substituted-1H-tetrazoles 8 is the reaction of azide ion with nitriles [ 20 ]. The literature is full of examples of this conversion method. They can be divided into three main categories using tin or silicon azides [ 21 ], acidic media [ 22 ], and strong Lewis acids [ 23 , 24 ]. In addition, all of the known methods use organic solvents, in particular, dipolar aprotic solvents such as DMF [ 25 ]. A new method for the synthesis of 5-substituted-1H-tetrazoles method was reported where compound 6 , water, sodium azide and zinc chloride were refluxed in a hood [ 26 , 27 , 28 ].
Several methods for the synthesis of tetrazoles are widely reported in the literature. The main synthetic routes to tetrazoles are outlined in Scheme 1 , Scheme 2 and Scheme 3 . Tetrazoles could be synthesized by the reaction of substituted amines 4 with triethyl orthoformate and sodium azide in dimethyl sulfoxide (DMSO) [ 10 , 11 ] ( Scheme 1 ). A new method to convert substituted amines into tetrazoles involves preparing functionalized superparamagnetic Fe 3 O 4 ·SiO 2 possessing high saturation magnetization [ 12 ].
3. Biological Activity of Tetrazolium Derivatives
Compounds derived from tetrazolium have received particular attention due to their pharmacological properties. Numerous studies have been published on the antibacterial and antifungal properties of these derivatives. Furthermore, these compounds also present anti-inflammatory, analgesic, anticancer, anticonvulsant, antihypertensive, hypoglycemic, antiparasitic, and antiviral activities. The aforementioned properties and the possibility to attach several structurally distinct substituents to the heterocycle ring to modify either the biological or physico-chemical properties of these compounds have prompted the use of this heterocycle as a template in many research programs aimed at the development of new bioactive compounds.
3.4. Anticonvulsant Activity
A potent inactivator of GABA-AT was synthesized ( ), which was shown to be a time- and concentration-dependent GABA-AT inhibitor. The study found low brain levels of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) can lead to seizure. Inhibition of GABA aminotransferase can increase the concentration of GABA and can terminate the convulsions. The Kinact/KI value for compound 94 was calculated to be 0.28 min&#;1·mM&#;1. Compound 94 also showed good lipophilicity (ClogP = &#;0.48) [77]. A new series of substituted tetrazoles were reported where all the synthesized compounds exhibited anticonvulsant activity against subcutaneous metrazole (ScMet) and maximal electroshock (MES) induced seizures in mice. Compounds 95 and 96 proved to be the most active compounds in this study, with special high activity in the ScMet test (% protection: 100% and 80%, respectively) [78].
Open in a separate windowA series of 5-alkoxytetrazolo-[1,5-c]thieno[2,3-e]pyrimidine derivatives were synthesized and evaluated for anticonvulsant activities. The pharmacological results showed that only four of the synthesized compounds had weak anticonvulsant activity. The more active compounds were 97 and 98 [79]. A new series of 6-alkyoxytetrazolo[5,1-a]phthalazine derivatives was synthesized and their anticonvulsant activity evaluated. The pharmacological results showed that compound 99 was the most potential agent, with an ED50 value of 6.8 mg/kg and a TD50 value of 456.4 mg/kg. The protective index (PI = TD50/ED50) for compound 99 was 67.1, which was significantly higher than that for the reference drug carbamazepine (PI = 6.4) [80]. In our laboratory studies of antiepileptic drugs, this was found to be the best active compound in ten years. It is in preclinical stages and is expected to be eventually registered as an approved drug.
3.5. Antihypertensive Activity
A novel nonpeptide angiotensin AT1 receptor antagonist was reported ( ). The pharmacology results demonstrated that compound 100 inhibited [125I] angiotensin II binding to AT1 receptors in rat liver membranes (Ki = 2.5 ± 0.5 nM) and did not interact with AT2 receptors in bovine cerebellar membranes. Compound 100 inhibited the contractile response to angiotensin II (pD(2)' values: 7.43 and 7.29, respectively) with a significant reduction in the maximum. The study suggested that compound 100 may be useful for treatment of hypertension [81,82]. An angiotensin II receptor antagonist which is selectivity for the AT1 receptor subtype was also reported. The concentration of compound 101 that inhibited the binding of [125I] Ang II to the AT1 receptor from rat adrenal cortex by 50% (IC50) was 0.13 nM, compared with 80.0 nM for losartan. Compound 101 showed excellent inhibitory activity in the contraction of isolated rabbit thoracic aorta contrasted with other ARBs such as losartan and candesartan. The antihypertensive effect of compound 101 was also verified to be maintained for 24 h [83,84]. Arhancet et al., reported the structure-activity relationships of the novel series of cyanoester dihydropyridines. Compound 102 showed improved in vitro metabolic stability and solubility without CYP inhibition liability. On the basis of its MR potency and favorable in vitro pharmacokinetic profile, with its moderate clearance and good half-life, compound 102 might be a suitable candidate for in vivo efficacy studies [85].
Open in a separate window3.6. Hypoglycemic Activity
Novel tetrazole-bearing N-glycosides were designed and synthesized as SGLT2 inhibitors ( ). Their hypoglycemic activity has been tested in vivo by a mice oral glucose tolerance test (OGTT). Two compounds were found to be more potent than the positive control dapagliflozin. The inhibition rates of blood glucose levels in mice OGTT for compounds 103 and 104 were 73.9% and 77.0% as compared with dapagliflozin (68.3%) [86]. Momose et al. prepared a series of 5-(4-alkoxyphenyl-alkyl)-1H-tetrazole derivatives and evaluated their antidiabetic effects in two genetically obese and diabetic animal models, KKAy mice and Wistar fatty rats. A large number of the compounds showed potent glucose and lipid lowering activities in KKAy mice. In particular, compound 105 had potent glucose lowering activity (ED25 = 0. mg·kg&#;1·d&#;1), being 72 times more active than pioglitazone hydrochloride (ED25 = 6.0 mg·kg&#;1·d&#;1). This compound also showed strong glucose lowering (ED25 = 0. mg·kg&#;1·d&#;1) and lipid lowering effects (ED25 = 0. mg·kg&#;1·d&#;1) in Wistar fatty rats. The antidiabetic effects of the compound 105 are considered to be due to its potent agonistic activity (EC50 = 6.75 nM) for peroxisome proliferator-activated receptorγ (PPARγ) [87]. Pegklidou et al., synthesized a novel series of pyrrole based on chemotypes and evaluated their activity as selective aldose reductase inhibitors. The data indicated that the presented chemotypes 106 and 107 are promising lead compounds for the development of selective aldose reductase inhibitors, targeting the long-term complications of diabetes mellitus [88].
Open in a separate window3.7. Antiparasitic Activity
A series of compounds bearing a tetrazole and triazine ring structures conjugated with a SO2NH function were synthesized ( ) and tested for their antiamoebic activity. Compounds 108 and 109 were the least cytotoxic (IC50 > 100 μM) and excellent Entamoeba histolytica inhibitors with IC50 values of 1.05 μM and 1.0 2 μM, respectively [89]. A novel series of pyrazoline derivatives were synthesized and screened in vitro to determine the effect on the growth of HM1:IMSS strain of Entamoeba histolytica. Compound 110 had potent antiamoebic activity (IC50= 0.86 μM), the least cytotoxicity (IC50 = >100 μM) and safety index value of >116.28, which was nearly twice better than metronidazole (IC50 > 55.55 μM) [90]. A new series of 5-(1-aryl-3-methyl-1H-pyrazol-4-yl)-1H-tetrazole derivatives and their precursor 1-aryl-3-methyl-1H-pyrazole-4-carbonitriles were synthesized and evaluated as in vitro antileishmanials against Leishmania braziliensis and Leishmania amazonensis promastigotes. In parallel, the cytotoxicity of these compounds was evaluated on the RAW 264.7 cell line. The results showed that among the assayed compounds the substituted 3-chlorophenyl (compound 111) (IC50/24 h = 15 ± 0.14 μM) and 3,4-dichlorophenyl (compound 112) (IC50/24 h = 26 ± 0.09 μM) tetrazoles were the most potent against L. braziliensis promastigotes, as compared with the reference drug pentamidine, which presented IC50 = 13 ± 0.04 μM. In addition, compound 111 and 112 were less cytotoxic than pentamidine [91].
Open in a separate window3.8. Antiviral Activity
Hutchinson and Naylor prepared 5-(phosphonomethyl)-1H-tetrazole and a number of related tetrazoles ( ) and investigated their effects on the replication of Herpes Simplex Viruses-1 and -2 as well as their abilities to inhibit the DNA polymerases induced by these viruses and the RNA transcriptase activity of influenza virus A. The thio-analogue 113 was a good chelator of zinc ions (pKd' > 6, the determination of pKd' values related to the strength of binding of zinc ions to phosphonates was by gel filtration) and was a more effective inhibitor of HSV-1 DNA polymerase and influenza RNA tranlscriptase [92]. A series of novel tetrazoles containing 1,2,3-thiadiazole derivatives were sythesized. The bioassay tests indicated that most of the target compounds had higher anti-TMV activity than that of ribavirin at 100 μg/mL. Compounds 114, 115 and 116 also showed equivalent protection effect to ribavirin in vivo at 100 μg/mL. These studies indicated that the newly synthesized tetrazole-containing 1,2,3-thiadiazole derivatives possessed good potential bioactivities, and were worthy of further study in pesticide development [93]. 7-(2H-Tetrazol-5-yl)-1H-indole (117) was found to be a potent inhibitor of HIV-1 attachment but the compound was lack of oral bioavailability in rats. The cause of the low exposure was believed to be poor absorption attributed to the acidic nature of the tetrazole moiety [94,95].
Open in a separate window3.9. Other Miscellaneous Activities
Other tetrazolium compounds that have miscellaneous activities were synthesized ( and ). Karabanovich et al., reported a new class of highly potent antituberculosis agents, 1-substituted-5-[(3,5-dinitrobenzyl)sulfanyl]-1H-tetrazoles 118 and their oxa- and selenyl-analogs 119 and 120. Antimycobacterial activities reached MIC values of 1 μM against M. tuberculosis CNCTC My 331/88 and 0.25&#;1 μM against six multi-drug resistant clinically isolated strains of M. tuberculosis; these compounds also exhibited no cross-resistance with common anti-TB drugs. Furthermore, these compounds possessed similar activity towards both INH-susceptible and INH-resistant strains of non-tuberculous M. kansasii. Moreover, compounds of series 118, 119 and 120 exhibited highly selective antimycobacterial effects because they exhibit no antibacterial or antifungal effects and exhibit low toxicity on selected mammalian cell lines with IC50 values upwards of 30 μM [96]. Kikuchi et al., investigated an antiglaucoma ophthalmic agent 121 which is an angiotensin AT1 receptor antagonist with a molecular weight of approximately 446. The studies revealed that compound 121 exhibits a solubilizing effect upon insoluble additives as generally seen in detergents. Furthermore, in vitro permeability across rabbit corneal membrane for compound 121 decreased at higher concentrations [97]. Adibi et al., sythesized a series of catecholthioethers having benzoxazole and tetrazole moieties. The antioxidant activity was assessed using two methods, including 1,1-biphenyl-2-picrylhydrazyl (DPPH) radical scavenging and reducing power assays according to the methods described in the literature. All the synthesized compounds except one exhibited very good antioxidant properties. They were also more potent than BHA and Trolox used as reference compounds. The IC50 of compound 122 that the best for antioxidant activity among tetrazolium compounds, with a value of 0.17. Furthermore, 122 could inhibit in vitro growth of Candida albicans having the same inhibitory activity as fluconazole (MIC value 4 mg/mL) [98]. Singh et al. synthesized several regioisomeric tetrazolylindole derivatives and screened them for their ER binding affinity, agonist (estrogenic), antagonist (antiestrogenic) and anti-implantation activities. Compound 123 showed 100% contraceptive efficacy at 10 mg/kg dose. At a lower dose of 5 mg/kg, it was only 67% effective however [99]. Li et al., prepared a novel series of N1 substituted tetrazole amides and showed them to be potent growth hormone (GH) secretagogues. Among them, the most potent analog 124 (EC50 = 0.2 nM) showed an increase in plasma GH levels of approximately 10-fold in an anesthetized IV rat model [100].
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