Aug. 06, 2024
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.
Several processes for producing 5-aminotetrazole are already known in the art. For example, Journal of Organic Chemistry,, () 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.
In addition, Journal of Organic Chemistry,, 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 September 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.wherein X represents I, HSOor 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.
D2 (Chemical Abstracts, vol. 96, no. 11, 15 March , Columbus Ohio, US: abstract no. t, page 593 column L; & CS-A-190 055) discloses the production of 5-substituted aminotetrazole from aminoguanidine sulfate 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.
DE-C-65 584 discloses the production of aminoguanidine from nitroguanidine.
Ullmann's Encyclopedia of Industrial Chemistry, 5th ed., , VCH, Weinheim, Vol. A12, p. 545-557, especially p. 551, Section 2.2 discloses a process for providing aminoguanidine bicarbonate from hydrazine and cyanimide.
Accordingly, 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:
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.
Accordingly, the present invention is a process for producing 5-aminotetrazole as defined by Claims 1 to 5 and comprises the steps of: (a) reacting hydrazine in a solvent with hydrochloric acid or sulfuric acid to form a solution of a salt of hydrazine; (b) reacting cyanamide with said solution of a salt of hydrazine to form aminoguanidine hydrochloride or sulfate, respectively; (c) adding thereto, without isolating the salt of aminoguanidine formed in step (b), hydrochloric acid or sulfuric acid and then a nitrite to form a salt of diazoguanidine; and (d) cyclizing the salt of diazoguanidine, without isolating from the reaction mixture of step (c), upon heating at a temperature of 70-95°C for 1-6 hours, to thereby produce the 5-aminotetrazole.
The present invention will be better understood from the description set forth below with reference to the accompanying drawings, wherein:
The 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.wherein X represents Cl, HSO, NO, HPO, 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 hydrochloric acid or sulfuric acid. From the economical viewpoints, the use of hydrochloric acid or sulfuric acid is most preferable. The salts of hydrazine usable in the present invention are hydrochloride and sulfate. 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 are hydrochloric acid or sulfuric acid. 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 70 - 95°C can be maintained during the reaction.
The reaction time of the cyclization is 1 to 6 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 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.
The present invention will now be further illustrated by, but is by no means limited to, the following Examples.
To a ml four necked flask provided with a thermometer and an agitating means, 65.0g (1.3 mole) of hydrazine-monohydrate was charged. While agitating, 131.8g (1.3 mole) of 36% by weight aqueous hydrochloric acid was added to neutralize and, then, 109.2g (1.3 mole) of 50% by weight aqueous cyanamide solution and 185g of water were dropwise added, followed by reacting at 85°C for 3 hours. After completion of the reaction, 121.6g of 36% by weight aqueous hydrochloric acid was added to the reaction mixture and at a reaction temperature of 40°C or less, 321.7g (1.2 mole) of 26% by weight aqueous sodium nitrite solution was dropwise added. After allowing to stand at room temperature over night, 48.5g (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 124.0g of 5-aminotetrazole in the crystalline form.
To the crystalline 5-aminotetrazole obtained above, 372.0g 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, 103.8g 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, 97.7g (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 5.12g 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, 4.21g 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.
To the apparatus similar to Example 1, 129.5g (1.0 mole) of hydrazine·1/2 sulfate and 25g of water were charged and 84.0g of 50% aqueous cyanamide solution was dropwise added, followed by reacting at 85°C for 3 hours. After completion of the reaction, 127.3g (0.5 mole) of 35% sulfuric acid was added and, in the similar manner as in Example 1, 73.3g (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 1 was repeated, except that crystalline cyanamide (purity = 98%) was used instead of 50% aqueous cyanamide solution. As a result, 97.1g (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.
To 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.
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.
To a ml four necked flask provided with a thermometer and an agitating means, 482.4g (3.00 mole) of 35% by weight aqueous potassium hydroxide solution was charged and heated to 80°C. While agitating, 257.8g (3.00 mole) of 5-aminotetrazole in the form of powder was added. Thus, 739.0g 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 277.1g. 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 74.0g, 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.
To a ml four necked flask provided with a thermometer and an agitating means, 76.5g (0.90 mole) of 5-aminotetrazole and g of water was charged and heated to 80°C. Thereafter, 363.2g (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 .0g 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 65.0g. 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 17.3g, 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.
To a ml four necked flask provided with a thermometer and an agitating means, 103.0g (1.20 mole) of 5-aminotetrazole and 300.0g of methanol were charged. 5-aminotetrazole and 300.0g of methanol were charged. While agitating, 379.2g (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 301g of methanol, the reaction mixture was cooled to 20°C and the reaction mixture was separated by a suction filtration. Thus, 112.2g of the wet crystal was obtained. The wet crystal thus obtained was dried at 80°C for 12 hours to obtain 100.1g (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.
To a ml four necked flask provided with a thermometer and an agitating means, 76.5g (0.90 mole) of 5-aminotetrazole and 450.0g of water were charged. While agitating, 360.0g (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 752.3g 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 129.0g 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.
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
The exothermic initiating temperature of a differential scanning calorimeter
The results are shown in the following Table 1.
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.
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Dinitraminic acid (HN(NO 2 ) 2 , HDN) was prepared by ion exchange chromatography and acid&#;base reaction with basic copper(II) carbonate allowed the in situ preparation of copper(II) dinitramide, which was reacted with twelve nitrogen&#;rich ligands, for example, 4&#;amino&#;1,2,4&#;triazole, 1&#;methyl&#;5H&#;tetrazole, di(5H&#;tetrazolyl)&#;methane/&#;ethane/&#;propane/&#;butane. Nine of the complexes were investigated by low&#;temperature X&#;ray diffraction. In addition, all compounds were investigated by infrared spectroscopy (IR), differential thermal analysis (DTA), elemental analysis (EA) and thermogravimetric analysis (TGA) for selected compounds. Furthermore, investigations of the materials were carried out regarding their sensitivity toward impact (IS), friction (FS), ball drop impact (BDIS) and electrostatic discharge (ESD). In addition, hot plate and hot needle tests were performed. Complex [Cu(AMT) 4 (H 2 O)](DN) 2 , based on 1&#;amino&#;5&#;methyltetrazole (AMT), is most outstanding for its detonative behavior and thus also capable of initiating PETN in classical initiation experiments. Laser ignition experiments at a wavelength of 915 nm were performed for all substances and solid&#;state UV&#;Vis spectra were recorded to apprehend the ignition mechanism.
The dinitramide anion was made accessible for complexation through the use of dinitraminic acid and basic copper(II) carbonate. The in situ prepared copper dinitramide was complexed by 13 different highly endothermic tri&#; and tetrazole ligands. By the choice of ligand, complexes were obtained that possess thermal stability exceeding 200 degrees Celsius, one even capable of initiating pentaerythritol tetranitrate (PETN). The examined compounds were successfully ignited in laser experiments, with one complex even detonating.
The complexes synthesized in this way can be used in a wide range of applications. The easily accessible anion is not only extending the field of ECC with this method, but the resulting complexes can also serve as burn rate catalysts in solid propellants and as halogen&#; and lead&#;free explosives. In addition to this, the complexes can also be used in the field of laser&#;ignitable compounds. [16]
The major task that needs to be dealt with when synthesizing dinitramine complexes can be explained by the corresponding tetraammine copper(II) compound ( 2 ) presented in Figure . The coordination compound was already described in and, due to the impossible isolation of an elemental pure sample, was only examined by X&#;ray diffraction, 14 N NMR, and vibrational spectroscopy. [15] The reason for this is probably the reaction that precedes the formation of the complex. Typically, a mixture of ammonium dinitramide with any copper(II) salt is reacted with the respective ligand. [9b] Alternatively, a copper(II) complex with any anion and the desired ligand is formed in solution and a dinitramide salt is added. [8] Thus, in every case, ions are left behind which can contaminate the sample or lead to a wrong composition of the complex. In this work the problem was solved using ion exchangers, which enables the simple production of dinitraminic acid (HDN). Reaction with metal carbonates allows the preparation of pure metal dinitramide salts without interfering anions in situ, which was already shown by Lukyanov et al. by reacting HDN with silver carbonate. [5b] However, the dinitraminic acid was preferably obtained by the injection of hydrogen chloride into a solution of KDN. The idea of an alternative preparation of an aqueous HDN solution was already shown by Bottaro et al. though the authors did not perform reactions with metal carbonates of the 3d series. [6]
The low thermal stability of dinitramine&#;based compounds (e. g., ADN=135 °C) is a known issue and a significant aspect that must be taken into account when designing new energetic materials based on this anion. [11] At this point, the concept of ECC is applied, since the adaptation of the properties, such as performance and thermal stability, of the formed coordination compounds can be readily tuned by changing the central metal, anion, or ligand.[ 12 , 13 ] Szimhardt et al. already showed that the implementation of propylene bridged ditetrazoles in complexes can increase thermal stability through the linking of the ligand between several metal centers. [9b] Furthermore, a comparison of the previously known complexes shows that probably none of them is able to successfully initiate PETN. Therefore, the focus should also lie on the incorporation of ligands that are known to enhance the performance of the complexes by their high positive heat of formation.[ 13b , 14 ]
To the best of our knowledge, only three azole&#;based transition metal complexes are known, two of which have been published by the Klapötke group. [9] Both show octahedral coordination geometries, although the one based on 5&#;(1&#;methylhydrazinyl)&#;1H&#;tetrazole is more clearly distorted (Figure ). Furthermore, an aminoguanidine&#;based complex is known, which exhibits a square planar coordination geometry rare for copper(II) compounds. [10]
Besides liquid fuel mixtures based on cryogenic or hypergolic reactions, ammonium dinitramide (ADN) is considered as a compound with high potential. [1] It was first synthesized in at the Zelinsky Institute of Organic Chemistry in Moscow. [4] However, information was kept under seal and published later in the course of time in the form of some publications.[ 4 , 5 ] Therefore, the anion was discovered by US scientists in the late s, independently of the Russians. [6] Since the salt contains no carbon or halogens, its decomposition products are mostly environmentally friendly. [7] This makes the dinitramide anion also a promising candidate for the use in halogen&#;free energetic coordination compounds (ECC). These materials could act not only as sensitive explosives but also as low carbon and oxygen&#;rich burn rate catalysts, for example, in airbags. Implementing the dinitramide function in 3d transition metal coordination compounds is not a new concept, for example Klapötke et al. published some dinitramide complexes based on 3&#;amino&#;1&#;nitroguanidines. [5b,8]]
The so&#;called ammonium perchlorate composite propellants (APCP) are ammonium perchlorate (AP, NH 4 ClO 4 ) (mostly mixed with HTPB and aluminum) based fuels in solid rocket motors. [1] At temperatures above 200 °C, AP decomposes mostly into gaseous chlorine, oxygen, nitrogen, and water due to the reducing effect of the ammonia cation, while the perchlorate anion acts as an oxidizing species. [2] Despite the toxicity of the perchlorate anion and its decomposition products, these mixtures are still widely used, mainly because of their cheap and easy preparation. Nevertheless, much research is being carried out on halogen&#;free rocket propellants and burn rate catalysts, [3] with some approaches to replacing AP already well advanced. [1]
Every coordination compound was investigated by differential thermal analysis (DTA) at a linear heating rate of 5&#;°C&#;min&#;1 in the range of 25&#;400&#;°C. The observed decomposition temperatures as well as endothermic events (melting or loss of aqua ligands and crystal water) are listed in Table&#; . In addition, thermogravimetric (TGA) measurements at the same heating rate and temperature range were carried out for compounds 2, 4, 5, 8, 9, 13, and 15 (Figures&#; , S10&#;S11) in order to investigate the behavior of the complexes on heating in more detail. The DTA plots of compounds 2&#;15 as well as additional information regarding the thermal stabilities can be found in the in the Supporting Information (Figures&#;S7&#;S9).
No.
Tendo [°C][b]
Texo [°C][c]
No.
Tendo [°C][b]
Texo [°C][c]
2
66
179
9
97
165
3
&#;
203
10
&#;
147
4
129
195
11
&#;
164
5
114
159
12
&#;
150
6
&#;
106
13
113
152
7
65
114
14
&#;
141
8
89*
89*
15
97
147
Open in a separate windowOpen in a separate windowEndothermic events were observed for eight of the fourteen investigated compounds. As verified by TGA, the endothermic events of 4, 9, and 13 represent the loss of aqua ligands or, in the case of compound 7, the loss of crystal water. Thermogravimetric measurements of the compounds 2, 5, 8, and 15 indicated no loss of mass before reaching the decomposition temperature of the complexes. This indicates that the endothermic events only represent melting points of the ECC 2, 5, and 15. The DTA measurement of complex 8 has an endothermic event immediately followed by an exothermic event, thus it is assumed that the loss of the aqua ligand (T endo=89&#;°C) simultaneously results in the decomposition of the complex. The reason for this is probably a square planar complex resulting from the loss of the ligand. Its stability is so low that decomposition occurs immediately after dehydration. In consequence, no mass loss prior to decomposition could be detected during the TG measurement since both events occur simultaneously.
The complex possessing the highest thermal stability is the ATRI based ECC 3 (T exo=203&#;°C). This is due to the bridging effect of the triazole ligands, each linking between two copper(II) centers. Similar effects can be observed for complexes 4 (T exo=195&#;°C), 9 (T exo=165&#;°C), and 11 (T exo=164&#;°C), although less evident. The remaining complexes with a bridging ligand motif show no signs of increased thermal stability. In fact, the exothermal events of complexes 2 (T exo=179&#;°C) and 5 (T exo=159&#;°C), both based on non&#;bridging ligands, are higher. On the one hand, this is due to a known effect whereby complexes based on ditetrazoles exhibit decreasing thermal stability as the alkyl chain becomes longer.[9c] This effect can also be observed in the comparison of the ditetrazoles prepared in this work (Figure&#; ). On the other hand, effects such as the low decomposition temperature of the ligand itself (ECC 10), or the lower stability of the dehydrated species (compound 13) are reasons for lower thermal stabilities.[14] Nevertheless, the exothermic decomposition temperature of compound 3 clearly proofed, that a tuning of the compounds&#; thermal stability is possible through the choice of the suitable ligand.
Open in a separate windowIn addition, every compounds&#; sensitivity toward mechanical stimuli according to BAM standard methods[28] and electrostatic discharge were investigated and ranked in accordance with the UN recommendations on the transport of dangerous goods (Table&#; ).[29] Interestingly, complex 8 is one the most sensitive complex studied in terms of its sensitivity toward friction (FS=3&#;N). This is surprising, because usually the presence of water in energetic materials leads to desensitization, which seems to be equalized by the strong endothermic character of the ligand.[13] Similar sensitivities were observed for complexes 8, 9, and 10. The di(tetrazolyl)methane ligands (1,1&#;dtm&#;&&#;1,2&#;dtm) used in these complexes are known to form powerful but sensitive coordination compounds, which is why ECC 10 is the third most sensitive (FS=15&#;N), closely followed by coordination compound 9 (FS=40&#;N).[14] The high friction sensitivity of the compound is unusual, as noted for complex 8, because of the two aqua ligands. Regarding the other coordination compounds containing water ligands, it becomes clear that these are the least sensitive compounds besides complex 15 (FS=240&#;N). The high stability of the latter is due to the complex's high carbon content compared to the other ones. Also, worth mentioning is complex compound 6, which is the second most sensitive of the compounds tested regarding friction sensitivity or thermal stability (T exo=106&#;°C; FS=5&#;N, IS=2&#;J). The reason for this is probably the unusual structure of the complex and its anionic dinitramido ligands, which are bonded to the central metal via a nitrogen atom. Since this is the first case of a complex showing such coordination geometry known to the authors, a proof of this assumption by literature data is unfortunately not possible at this time.
&#;
No.
IS (J)[a]
BDIS (mJ)[b]
FS (N)[c]
ESD (mJ)[d]
[Cu(DN)2(NH3)4]
(2)
2
>200
50
[Cu(ATRI)3](DN)2
(3)
8
20
80
14
[Cu(BTRI)2(H2O)2](DN)2
(4)
7
83
144
181
[Cu(MTZ)6](DN)2
(5)
8
>200
120
203
[Cu(AET)2(DN)2]
(6)
2
28
5
250
[Cu(DN)2(MAT)4]&#;&#;&#;2 H2O
(7)
4
>200
80
>
[Cu(AMT)4(H2O)](DN)2
(8)
2
28
3
250
[Cu(1,1&#;dtm)2(H2O)2](DN)2
(9)
2
41
40
>
[Cu(1,2&#;dtm)3](DN)2
(10)
2
28
Boraychem supply professional and honest service.
15
270
[Cu(1,1&#;dte)3](DN)2
(11)
&#;1
28
72
76
[Cu(2,2&#;dte)3](DN)2
(12)
2
25
30
250
[Cu(H2O)2(idtp)2](DN)2
(13)
2
180
120
317
[Cu(DN)2(1,2&#;dtp)2]
(14)
2
>200
60
840
[Cu(dtb)3](DN)2
(15)
3
>200
240
>
Open in a separate windowThe effect of the carbon content on the properties of a complex, especially the stability against mechanical stimuli, can be illustrated using the example of dinitramide complexes investigated in this work. Together with the complex already published by Szimhardt et&#; al., the complete series of copper dinitramide ECC based on ditetrazole ligands from di(tetrazol&#;1&#;yl)methane to 1,4&#;di(tetrazol&#;1&#;yl)butane is known.[9b]
The trends shown in Figure&#; represent a fundamental concept of ECC. As the length of the carbon chain increases, sensitivity toward impact and friction decreases, whilst thermal stability drops. However, the effect of the different coordination geometry in compound 9, compared to the other complexes, should be noted. A comparison of the sensitivity to electrostatic discharge is less meaningful since this is extremely dependent on the grain size. Ball drop impact sensitivity of [Cu(1,1&#;dtp)3](DN)2 was determined and impact and friction sensitivity were redetermined using the same batch to reduce grain size influences.
Apart from the trend shown in Figure&#; , there are no other significant sensitivity patterns with respect to impact sensitivity. According to the UN recommendations on the transport of dangerous goods, every compound except 3, 4, 5, and 7 are ranked as very sensitive regarding impact sensitivity.[29] The remaining compounds must only be considered as sensitive. In terms of sensitivity toward friction, compounds 3 and 7 are also considered very sensitive, with ECC 6 and 8 being even extremely sensitive. The complexes 13 and 15 are only considered sensitive.
In addition to BAM sensitivities, the ball drop impact sensitivity (BDIS) according to MIL&#;STD &#;A (method ) was investigated.[31a] The aim was to obtain measured values which are more realistic than data obtained mainly with the BAM drop hammer. This method is known to suffer from some weaknesses, for example, the ignition of the substance by forming hotspots within the shells.[33] In the ball drop test, however, a steel ball with a defined spin is dropped onto an unconfined sample, spread over a thin layer of defined height (Figure&#; ).[31a]
Open in a separate windowExperiments were carried out for every coordination compound. The outcome is displayed in Table&#; . The sensitivities obtained for compounds 5 (IS=8&#;J, BDIS>200&#;mJ, FS=120&#;N), 6 (IS=2&#;J, BDIS=28&#;mJ, FS=5&#;N), 7 (IS=2&#;J, BDIS>28&#;mJ, FS=3&#;N), 13 (IS=2&#;J, BDIS=180&#;mJ, FS=120&#;N), and 15 (IS=3&#;J, BDIS>200&#;mJ, FS=240&#;N) are either very low, or very high, which is consistent with our earlier findings.[34] It is assumed that there is a strong correlation between low sensitivity toward friction and ball drop impact. However, in the case of compounds 2, 3, and 11 the results do not match our previous results. ECC 3 (IS=8&#;J, BDIS=20&#;mJ, FS=80&#;N) was not considered sensitive during BAM sensitivity measurements but was tested the most sensitive compound during ball drop testing. Whilst the tetrammine complex 2 (IS=2&#;J, BDIS>200&#;mJ, FS=50&#;N) was much more insensitive than expected the ball drop impact sensitivity on 11 (IS=1&#;J, BDIS=28&#;mJ, FS=72&#;N) correlates more with the BAM impact rating than with the friction sensitivity. This shows that the system of ball drop impact sensitivity has not yet been completely understood and that there are other substances that need to be investigated using this method in order to further expand our knowledge about this method and sensitivities of energetic materials in general. For safety reasons, different and unknown sensitivity values from external devices must be evaluated carefully.
A comparison of the complexes of this work with earlier work of our group on this area is difficult in most cases. Since strongly coordinating anions such as fulminate, azide, or various trinitrophenolates lead to significantly different coordination geometries, a comparison here is almost impossible. Therefore, the best way of making meaningful comparisons is probably with other oxidizing, weakly coordinating anions such as nitrate, chlorate, bromate or perchlorate. In the case of complexes 2, 4, 6, 9, 12, and 15, this is also not possible, since either no similarly structured complexes are known in the literature or have not been sufficiently investigated for their energetic parameters. In the cases in which a comparison was useful, it was found that apart from compound 11, which is 0.5&#;J more sensitive than the respective chlorate and perchlorate complexes, all dinitramide based ECCs are less sensitive than the analogous chlorate, bromate or perchlorate complexes. The only suitable nitrate complex [Cu(MTZ)6](NO3)2 on the other side is less sensitive than ECC 5.
Hot plate and hot needle tests were performed as an initial test to get an insight into each compounds&#; deflagration to detonation transition (DDT), which is a very important property of primary explosives. Investigations on DDT allow conclusions to be drawn on how well a primary is capable of initiating a booster charge such as PETN. The hot plate test displays the behavior of a compound during fast heating (Figure&#; , left). Hot needle tests indicate the performance of a sample during slight confinement (Figure&#; , right).
Open in a separate windowDetails on the process and further high&#;speed images of the experiments can be found in the General Methods in the Supporting Information (Figures&#;S7&#;S19). The outcome of each test is summarized in Table&#; . With the exception of 2, 3, 4, and 15, all ECC examined showed at least a deflagration in both initial experiments. These are very promising findings and the basis for further tests such as the initiation of pentaerythritol tetranitrate (PETN) or laser&#;based ignitions. Since complex 8 detonated during the hot needle test and the complexes 6, 9, 10 and 11 showed very strong deflagrations, those compounds were investigated as lead azide (LA, Pb(N3)2) substitutes.
&#;
Initial Testing
PETN Initiation Experiment
&#;
Initial Testing
PETN Initiation Experiment
&#;
HP
HN
&#;
HP
HN
&#;
2
dec.
dec.
&#;
9
defl.
defl.
negative
3
defl.
dec.
&#;
10
defl.
defl.
negative
4
defl.
dec.
&#;
11
defl.
defl.
negative
5
defl.
defl.
&#;
12
defl.
defl.
&#;
6
defl.
defl.
negative
13
defl.
defl.
&#;
7
defl.
defl.
&#;
14
defl.
defl.
&#;
8
defl.
det.
positive
15
dec.
dec.
&#;
Open in a separate windowTo carry out the initiation experiments, 200&#;mg of PETN were pressed into a copper shell and initiated with 50&#;mg of the substance to be investigated using a Type A electric igniter. A positive result, as observed in the case of ECC 8, is indicated by a hole in the copper plate (Figure&#; ). This clearly proved that by choosing the appropriate ligand, the power of the complex can be increased to a level capable of initiating PETN. A test of compound 11 indicated that this compound is close to being capable of initiating PETN. A modification of the test, for example, a variation of the particle size or quantity, could resolve this problem. Further details on the procedure can be found in the General Methods of the Supporting Information.
Open in a separate windowBesides the classical ignition methods by flame, as used in initiation experiments, or by mechanical stimuli, as found in percussion caps, more and more research is performed in the field of alternative ignition methods. One of these fields where ECC are already established are laser&#;based ignitions.[16] Especially regarding the dinitramide anion as part of ECC, there is evidence that copper(II) complexes based on this system respond to laser radiation.[9a, 9b, 9c]
The principle of laser&#;based ignition of primary explosives and priming mixtures has a great advantage over classical mechanical ignition. For a mechanical initiation, an impact or for primers frictional force must be generated. The substances used for this must therefore have a suitable mechanical sensitivity. For the most commonly used primary explosives lead azide (LA RD&#;) and lead styphnate (LS) these sensitivities were determined to 0.45&#;1&#;N and 7&#;8&#;J (LS) as well as &#;0.1&#;N and 4&#;J (LA RD&#;).[34, 35] For explosives ignited by laser irradiation, however, less sensitive substances are also suitable, which drastically reduces the risk potential during production, processing, and storage of the respective energetic materials.
In this work, every compound was investigated for its behavior when irradiated with a laser beam. The outcome of each test, together with the applied energy, is shown in Table&#; . Further information on the test setup and procedure can be found in the General Methods in the Supporting Information. With the exception of compound 12, all complexes showed a reaction toward the laser irradiation. The result of such examination, in this case the result of the testing of compound 5, is shown in Figure&#; . Further high&#;speed recordings of all compounds can be found in the Supporting Information (Figures&#;S20&#;26).
&#;
Laser Ignition Experiments, E (mJ)[a,b]
&#;
Laser Ignition Experiments, E (mJ)[a,b]
&#;
4.5
30
51
126
&#;
30
51
67.5
2
&#;
&#;
dec.
&#;
9
defl.
&#;
&#;
3
&#;
&#;
defl.
defl.
10
defl.
&#;
&#;
4
&#;
&#;
dec.
&#;
11
&#;
defl.
defl.
5
defl.
&#;
defl.
&#;
12
dec.
&#;
&#;
6
&#;
defl.
&#;
&#;
13
&#;
dec.
dec.
7
&#;
defl.
&#;
&#;
14
dec.
&#;
&#;
8
&#;
det.
&#;
&#;
15
defl.
&#;
&#;
Open in a separate windowOpen in a separate windowThe outcome of each investigation differed significantly due to the applied ligand. Thus, especially complexes 2, 3, 13, 14, and 15 showed only weak reactions, which, considering the respective hot plate and hot needle tests of the substances, is within the expectations. Coordination compounds 5, 6, 8, 9, and 10, which are based on ligands known to form powerful complexes, showed significantly stronger reactions when irradiated by the laser, up to a detonation in the case of compound 8. However, based on these expectations, compound 12 in particular disappointed in terms of output upon laser irradiation.
As mentioned earlier, the complex based on 2,2&#;dte did not respond at all to radiation despite promising hot plate and hot needle tests. Only minimal decomposition was detected in the primer cap after completion of the test, with a bulk of the complex remaining unreacted. This is worth mentioning because complex 11, based on the isomeric ligand 1,1&#;dte, which has the same molecular formula, underwent strong deflagration during laser irradiation. Assuming that the decomposition of the sample in the laser is thermal in nature, the two&#;step slow decomposition observed during the DTA measurement could be a reason for the behavior (Figure&#;S9).
Except for compound 12, these results suggest a possible use as potential laser&#;ignitable explosives and demonstrates again that by utilizing the concept of ECC, the performance of the dinitramide anion in complexes can be adjusted by selecting the appropriate ligand system. As the mechanisms behind laser ignition (most probably thermal ignition) are still not fully understood, UV&#;Vis spectra were recorded in the solid state for selected compounds. Particular emphasis was placed on the wavelength range corresponding to that of the laser when evaluating the spectra. Details on this, as well as all spectra, can be found in the Supporting Information (Table&#;S4, Figure&#;S27&#;S28).
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