Ammonium Dinitramide NH4N3O4 [Published]
AndersHoveland
Acolyte
I you are interested in the chemistry of rockets and things that go "boom", it is strongly rocommended that you save a copy of this post for yourself, because this is the best information about making the salt you will ever find. Totse will not last forever!
Ammonium dinitramide, with the structure NH4[+] [-]N(NO2)2, is an energetic oxidizing salt which has been investigated for use in propellents. It is, however, significantly more sensitive to detonation than ammonim perchlorate during combustion. Ammonium dinitramide with aluminum powder has about an 11% higher specific impulse than ammonium perchlorate.
Below are five different preparation routes for the compound:
Preparation A
17g potassium sulfamate was added in small portions (0.5- 1 g ) to a mixture of 16mL 98% concentrated sulfuric acid and 45 mL fuming nitric acid, with continual stirring of the mixture. The mixture was kept between (minus) -35 and -45 degC, using an ice bath consisting of dry ice and methylene chloride. (The reaction temperature need only be below -25 degC, if care is taken to avoid overheating) The viscocity increased as the reaction proceeded, and potassium bisulfate precipitated. Dinitramidic acid is not stable under acidic conditions so the pH must subsequently be raised to avoid decomposition. A solution of cold potassium hydroxide was slowly added to the reaction mixture, again with constant stirring, with the mixture still cooled in the ice bath. The temperature was not allowed to rise above 0degC. The solution becomes a greenish yellow color, indicating that the acids in solution are nearly neutralized. Further solution of potassium hydroxide was added until the pH reached 8 (weakly basic).
The reaction mixture allowed to evaporate until dry. The dry powder remaining was extracted with acetone, then 100mL pure isopropyl alcohol was added to the acetone solution. The mixture is again allowed to evaporate. As the acetone first evaporates out, the potassium dinitramide will precipitate out of the isopropyl alcohol. The crystals were filtered from the solution and dried in an oven at 70 degC. 10.7 grams (60% yield) of potassium dinitramide is obtained from this procedure. The crystals melt at 130.5 degC.
1g potassium dinitramide and 1g ammonium sulfate were individually dissolved in two separate portions of 2mL water each. The two solutions were then mixed, resulting in a white precipitate of potassium sulfate. 20mL of isopropyl alcohol was added to the solution, then the potassium sulfate was filtered out. The remaining solvent that passed through the filter was evaporated under reduced pressure. The product from the evaporation was slightly moist. It was next dissolved in more isopropyl alcohol. This solution was poured into petroleum ether, at which point ammonium dinitramide precipitated out. The precipitate was filtered out and dried at 50degC. 0.68 grams ammonium dinitramide is obtained from this procedure (80% yield). The crystals have a melting point of 91 degC.
Note
Maximum yields of dinitramidic acid were obtained when he mole ratios of sulfuric to nitric acid are 2 : 7, with a nitration time between 23-25 minutes.
Preparation B
Alternatively, ammonium sulfamate may be used in the nitration, and ammonium hydroxide can then be used to neutralize the mixture. This more direct procedure, however, gives only a 40% yield, and the ammonium dinitramide will contain ammonium nitrate impurities, which lowers the observed melting point to 86degC.
Sulfamic acid has the formula HOSO2NH2, and its salts can be prepared from the pyrosulfate (K2S2O7) with dry NH3 gas, or by direct reaction between SO3 and NH3 (reaction is extremely violent!)
Preparation C
Into a 250 mL Erlenmeyer flask combine 3 g of potassium dinitramide and 3 g of finely powdered ammonium sulfate. Add 100 mL of isopropyl alcohol and heat the flask, while stirring, until all of the solids dissolve. Place the flask in a cold water bath to precipitate the byproduct of potassium sulfate. Filter to remove the crystals of sulfate and gently heat the filtrate to concentrate it to a fraction of its volume. Pour the concentrate into a beaker containing an excess of petroleum ether to precipitate ammonium dinitramide. Filter to collect the crystals and dry them in an oven at 50 C.
Preparation D
Prepare a mixture of 7.5 g of ammonium N-nitrourethane suspended in 200 mL of methylene chloride. Cool this mixture to -50 C in an acetone-dry ice bath. Prepare a second mixture of 45 mL of dinitrogen tetroxide in 200 mL of dry methylene chloride. Cool this mixture to -78 C in an acetone-dry ice bath. Bubble ozone into the second mixture, while stirring, until it is a dark blue color. While bubbling the ozone allow the mixture to warm up to -30 C. The mixture will now consist of dinitrogen pentoxide in methylene chloride.
Combine the two mixtures and let them sit for 1 hour. During this time the temperature of the reaction mixture is allowed to warm to -30 C. Bubble ammonia gas into the mixture to raise the pH to 10. Filter to collect any insoluble material and add it to a beaker containing 150 mL of acetonitrile. Stir the acetonitrile mixture for 20 minutes before filtering to remove any remaining undissolved impurities.
The filtrate is poured into a 2.5cm by 10cm column containing 230-400 mesh silica gel. The ammonium dinitramide is eluted by adding acetonitrile. The resulting eluted filtrate is concentrated to 30 mL and treated with 30 mL of chloroform to precipitate pure ammonium dinitramide. The crystals are filtered to collect them and allowed to dry. Final yield is about 4 g or 60%.
Preparation E
Prepare a mixture of 8.8 g of hydrofluoric acid and 40 g of ethylnitrate in 300 mL of dry nitromethane. Place this mixture in a salt-ice bath and cool to 10 C. Slowly add 100 g of boron trifluoride to the mixture while keeping the temperature between 10 and 15 C. A few minutes after the addition filter to collect the crystals of nitronium tetrafluorate that form. Wash the crystals with two 400 mL portions of a 1:1 mixture of methylene chloride and nitromethane, and then with one 400 mL portion of methylene chloride.
Place the nitronium tetrafluorate crystals into a beaker containing 400 mL of methylene chloride. Cool the contents to -78 C in an acetone-dry ice bath. Bubble 35 g of anhydrous ammonia into the beaker over a period of 2 hours while stirring. Continue stirring the mixture for 12 hours while allowing it to warm to room temperature. Filter to collect the solid material and wash it with 400 mL of methylene chloride. Add the crystals to 150 mL of acetone and stir for 1 hour. Add 150 mL of ethyl acetate to the mixture and filter to remove any undissolved material. Gently heat the filtrate solution to dryness to obtain crude ammonium dinitramide. The ammonium dinitramide can be purified by recrystallizing from n-butanol. Final yield is about 5.5 g or 21% yield.
Note about the Preparation of Nitronium Tetrafluoroborate
Nitronium tetrafluoroborate is a useful nitrating agent which has several advantages over nitric acid. There are also some nitration reactions where the presence of the nitrate ion would prevent the desired product from forming. Nitronium tetrafluoroborate is a solid ionic compound, with the formula NO2(+) BF4(-). Nitronium tetrafluoroborate can be prepared by adding a mixture of anhydrous hydrogen fluoride gas and boron trifluoride to a solution of either highly concentrated nitric acid or nitrogen pentoxide dissolved in nitromethane.
WARNING: Rubber gloves, an apron, and a plastic face mask are strongly recommended. All operations should be carried out in a hood. If hydrogen fluoride comes in contact with the skin, the contacted area should be thoroughly washed with water and then immersed in ice water while the patient is taken to rushed to the emergency department. Burns caused by hydrogen fluoride may not be noticed for several hours, by which time serious tissue damage may have occurred.
Note: Any operations involving liquid hydrogen fluoride must be carried out with equipment resisting hydrogen fluoride, such as fused silica, polyolefin, monel steel, or teflon. Kel-F grease is recommended for ground-glass joints. Nitronium tetrafluoroborate slowly attacks silicone stopcock grease, causing air to enter the flask. After completion of the reaction, all equipment should be washed with plenty of water.
A 1-Liter three-necked polyolefin flask is provided with a short inlet tube for nitrogen, a long inlet tube for gaseous boron trifluoride, a drying tube, and a magnetic stirring bar. The flask is immersed in an ice-salt bath and flushed with dry nitrogen. Under a gentle stream of nitrogen and with stirring, the flask is charged with 400 ml. of methylene chloride, 41 ml. (65.5 g., 1.00 mole) of red fuming nitric acid (95%), and 22 ml. (22 g., 1.10 moles) of cold, liquid, anhydrous hydrogen fluoride. 5. It is convenient to condense anhydrous hydrogen fluoride, b.p. 19.5°, from a cylinder into a small calibrated polyolefin flask immersed in a mixture of dry ice and acetone. As hydrogen fluoride is very hygroscopic, it should be carefully protected from atmospheric moisture, preferably by maintaining an atmosphere of dry nitrogen over it, otherwise by means of a drying tube. The hydrogen fluoride is then simply poured into the reaction flask.
Gaseous boron trifluoride (136 g., 2.00 moles) from a cylinder mounted on a scale is bubbled into the stirred, cooled reaction mixture. (The temperature of the reaction is not critical, but the reaction is slower at higher temperatures because of the lower solubility of boron trifluoride in the solvent). The first mole is passed in rather quickly (in about 10 minutes). When approximately 1 mole has been absorbed, copious white fumes begin to appear at the exit, and the rate of flow is diminished so that it takes about 1 hour to pass in the second mole; even at this slow rate, there is considerable fuming at the exit. After all the boron trifluoride has been introduced, the mixture is allowed to stand in the cooling bath under a slow stream of nitrogen for 1.5 hours. The mixture is swirled, and the suspended product is separated from the supernatant liquid by means of a medium-porosity, sintered-glass Buchner funnel. Note that since free hydrogen fluoride is no longer present, filtration can be carried out with glass or porcelain equipment.
The gooey solid remaining in the flask is transferred to the funnel with the aid of two 50-ml. portions of nitromethane. The solid on the funnel, nitronium tetrafluoroborate, is washed successively with two 100-ml. portions of nitromethane and two 100-ml. portions of methylene chloride. In order to protect the salt from atmospheric moisture during the washing procedure, suction is always stopped while the salt is still moist. The moist salt is transferred to a round-bottomed flask and dried by evaporating the solvent. At the end of the procedure the flask can be gently heated to 40–50°C (Nitronium tetrafluoroborate is thermally stable up to 170°. Above this temperature it starts to dissociate into nitryl fluoride and boron trifluoride.) The yield of colorless nitronium tetrafluoroborate is 85–106 g. (64–80%) It is stored in a wide-mouthed polyolefin bottle with a screw cap. The edge of the cap is sealed with paraffin wax after it is screwed on. Nitronium tetrafluoroborate is very hygroscopic. It is stable as long as it is anhydrous, but it is decomposed by moisture, and all transfers should be in a dry box.
Nitronium tetrafluoroborate slowly attacks polyethylene and polypropylene, but apparatus made of these materials will last for several preparations of the salt.
The last part of the procedure can be used to purify nitronium tetrafluoroborate that has picked up water on standing. The impure salt is washed twice with nitromethane, twice with methylene chloride, and is dried under reduced pressure.
Making Boron Trifluoride BF3
Boron trifluoride is a very toxic gas, which readily reacts with water to form metaboric acid and Fluoroboric acid, which then can further hydrolyze if excess water is present. It is a strong fluoride ion abductor, meaning it will pull a fluorine atom from many covalent compounds to form the tetrafluoroborate anion (BF4-), while leaving a positively charged cation. However, boron trifluoride is not as powerful of an abductor as antimony pentafluoride, as demonstrated by its unreactivity towards trichlorofluoromethane.
Boron trifluoride may be prepared by heating a mixture of boric oxide and calcium fluoride with concentrated sulfuric acid. It may also be prepared by mixing 5 parts of potassium borofluoride (KBF4) with 1 part finely powdered boric oxide, then heating with concentrated sulfuric acid. The boron trifluoride, can be collected over mercury. Potassium borofluoride may be produced by heating together 2 parts boric acid, 5 parts CaF2, and 10 parts conc H2SO4. The liquid is then cooled and filtered, and a solution of a potassium salt is added. Potassium borofluoride precipitates out, and may then be recrystallized from hot water. By this method it can be prepared as anhydrous hexagonal crystals. If it is prepared instead from hydrofluoric acid, boric acid, and K2CO3, a gelatinous mass forms instead, which however forms cubic octahedral and cubic dodecahedral crystals when heated to 100degC. Boron trifluoride also results from heating a mixture of boric oxide and calcium fluoride to a white heat in an iron pipe. Heating solid borofluorides to red heat, boron trifluoride is evolved, leaving behind metal fluorides.
Ammonium dinitramide, with the structure NH4[+] [-]N(NO2)2, is an energetic oxidizing salt which has been investigated for use in propellents. It is, however, significantly more sensitive to detonation than ammonim perchlorate during combustion. Ammonium dinitramide with aluminum powder has about an 11% higher specific impulse than ammonium perchlorate.
Below are five different preparation routes for the compound:
Preparation A
17g potassium sulfamate was added in small portions (0.5- 1 g ) to a mixture of 16mL 98% concentrated sulfuric acid and 45 mL fuming nitric acid, with continual stirring of the mixture. The mixture was kept between (minus) -35 and -45 degC, using an ice bath consisting of dry ice and methylene chloride. (The reaction temperature need only be below -25 degC, if care is taken to avoid overheating) The viscocity increased as the reaction proceeded, and potassium bisulfate precipitated. Dinitramidic acid is not stable under acidic conditions so the pH must subsequently be raised to avoid decomposition. A solution of cold potassium hydroxide was slowly added to the reaction mixture, again with constant stirring, with the mixture still cooled in the ice bath. The temperature was not allowed to rise above 0degC. The solution becomes a greenish yellow color, indicating that the acids in solution are nearly neutralized. Further solution of potassium hydroxide was added until the pH reached 8 (weakly basic).
The reaction mixture allowed to evaporate until dry. The dry powder remaining was extracted with acetone, then 100mL pure isopropyl alcohol was added to the acetone solution. The mixture is again allowed to evaporate. As the acetone first evaporates out, the potassium dinitramide will precipitate out of the isopropyl alcohol. The crystals were filtered from the solution and dried in an oven at 70 degC. 10.7 grams (60% yield) of potassium dinitramide is obtained from this procedure. The crystals melt at 130.5 degC.
1g potassium dinitramide and 1g ammonium sulfate were individually dissolved in two separate portions of 2mL water each. The two solutions were then mixed, resulting in a white precipitate of potassium sulfate. 20mL of isopropyl alcohol was added to the solution, then the potassium sulfate was filtered out. The remaining solvent that passed through the filter was evaporated under reduced pressure. The product from the evaporation was slightly moist. It was next dissolved in more isopropyl alcohol. This solution was poured into petroleum ether, at which point ammonium dinitramide precipitated out. The precipitate was filtered out and dried at 50degC. 0.68 grams ammonium dinitramide is obtained from this procedure (80% yield). The crystals have a melting point of 91 degC.
Note
Maximum yields of dinitramidic acid were obtained when he mole ratios of sulfuric to nitric acid are 2 : 7, with a nitration time between 23-25 minutes.
Preparation B
Alternatively, ammonium sulfamate may be used in the nitration, and ammonium hydroxide can then be used to neutralize the mixture. This more direct procedure, however, gives only a 40% yield, and the ammonium dinitramide will contain ammonium nitrate impurities, which lowers the observed melting point to 86degC.
Sulfamic acid has the formula HOSO2NH2, and its salts can be prepared from the pyrosulfate (K2S2O7) with dry NH3 gas, or by direct reaction between SO3 and NH3 (reaction is extremely violent!)
Preparation C
Into a 250 mL Erlenmeyer flask combine 3 g of potassium dinitramide and 3 g of finely powdered ammonium sulfate. Add 100 mL of isopropyl alcohol and heat the flask, while stirring, until all of the solids dissolve. Place the flask in a cold water bath to precipitate the byproduct of potassium sulfate. Filter to remove the crystals of sulfate and gently heat the filtrate to concentrate it to a fraction of its volume. Pour the concentrate into a beaker containing an excess of petroleum ether to precipitate ammonium dinitramide. Filter to collect the crystals and dry them in an oven at 50 C.
Preparation D
Prepare a mixture of 7.5 g of ammonium N-nitrourethane suspended in 200 mL of methylene chloride. Cool this mixture to -50 C in an acetone-dry ice bath. Prepare a second mixture of 45 mL of dinitrogen tetroxide in 200 mL of dry methylene chloride. Cool this mixture to -78 C in an acetone-dry ice bath. Bubble ozone into the second mixture, while stirring, until it is a dark blue color. While bubbling the ozone allow the mixture to warm up to -30 C. The mixture will now consist of dinitrogen pentoxide in methylene chloride.
Combine the two mixtures and let them sit for 1 hour. During this time the temperature of the reaction mixture is allowed to warm to -30 C. Bubble ammonia gas into the mixture to raise the pH to 10. Filter to collect any insoluble material and add it to a beaker containing 150 mL of acetonitrile. Stir the acetonitrile mixture for 20 minutes before filtering to remove any remaining undissolved impurities.
The filtrate is poured into a 2.5cm by 10cm column containing 230-400 mesh silica gel. The ammonium dinitramide is eluted by adding acetonitrile. The resulting eluted filtrate is concentrated to 30 mL and treated with 30 mL of chloroform to precipitate pure ammonium dinitramide. The crystals are filtered to collect them and allowed to dry. Final yield is about 4 g or 60%.
Preparation E
Prepare a mixture of 8.8 g of hydrofluoric acid and 40 g of ethylnitrate in 300 mL of dry nitromethane. Place this mixture in a salt-ice bath and cool to 10 C. Slowly add 100 g of boron trifluoride to the mixture while keeping the temperature between 10 and 15 C. A few minutes after the addition filter to collect the crystals of nitronium tetrafluorate that form. Wash the crystals with two 400 mL portions of a 1:1 mixture of methylene chloride and nitromethane, and then with one 400 mL portion of methylene chloride.
Place the nitronium tetrafluorate crystals into a beaker containing 400 mL of methylene chloride. Cool the contents to -78 C in an acetone-dry ice bath. Bubble 35 g of anhydrous ammonia into the beaker over a period of 2 hours while stirring. Continue stirring the mixture for 12 hours while allowing it to warm to room temperature. Filter to collect the solid material and wash it with 400 mL of methylene chloride. Add the crystals to 150 mL of acetone and stir for 1 hour. Add 150 mL of ethyl acetate to the mixture and filter to remove any undissolved material. Gently heat the filtrate solution to dryness to obtain crude ammonium dinitramide. The ammonium dinitramide can be purified by recrystallizing from n-butanol. Final yield is about 5.5 g or 21% yield.
Note about the Preparation of Nitronium Tetrafluoroborate
Nitronium tetrafluoroborate is a useful nitrating agent which has several advantages over nitric acid. There are also some nitration reactions where the presence of the nitrate ion would prevent the desired product from forming. Nitronium tetrafluoroborate is a solid ionic compound, with the formula NO2(+) BF4(-). Nitronium tetrafluoroborate can be prepared by adding a mixture of anhydrous hydrogen fluoride gas and boron trifluoride to a solution of either highly concentrated nitric acid or nitrogen pentoxide dissolved in nitromethane.
WARNING: Rubber gloves, an apron, and a plastic face mask are strongly recommended. All operations should be carried out in a hood. If hydrogen fluoride comes in contact with the skin, the contacted area should be thoroughly washed with water and then immersed in ice water while the patient is taken to rushed to the emergency department. Burns caused by hydrogen fluoride may not be noticed for several hours, by which time serious tissue damage may have occurred.
Note: Any operations involving liquid hydrogen fluoride must be carried out with equipment resisting hydrogen fluoride, such as fused silica, polyolefin, monel steel, or teflon. Kel-F grease is recommended for ground-glass joints. Nitronium tetrafluoroborate slowly attacks silicone stopcock grease, causing air to enter the flask. After completion of the reaction, all equipment should be washed with plenty of water.
A 1-Liter three-necked polyolefin flask is provided with a short inlet tube for nitrogen, a long inlet tube for gaseous boron trifluoride, a drying tube, and a magnetic stirring bar. The flask is immersed in an ice-salt bath and flushed with dry nitrogen. Under a gentle stream of nitrogen and with stirring, the flask is charged with 400 ml. of methylene chloride, 41 ml. (65.5 g., 1.00 mole) of red fuming nitric acid (95%), and 22 ml. (22 g., 1.10 moles) of cold, liquid, anhydrous hydrogen fluoride. 5. It is convenient to condense anhydrous hydrogen fluoride, b.p. 19.5°, from a cylinder into a small calibrated polyolefin flask immersed in a mixture of dry ice and acetone. As hydrogen fluoride is very hygroscopic, it should be carefully protected from atmospheric moisture, preferably by maintaining an atmosphere of dry nitrogen over it, otherwise by means of a drying tube. The hydrogen fluoride is then simply poured into the reaction flask.
Gaseous boron trifluoride (136 g., 2.00 moles) from a cylinder mounted on a scale is bubbled into the stirred, cooled reaction mixture. (The temperature of the reaction is not critical, but the reaction is slower at higher temperatures because of the lower solubility of boron trifluoride in the solvent). The first mole is passed in rather quickly (in about 10 minutes). When approximately 1 mole has been absorbed, copious white fumes begin to appear at the exit, and the rate of flow is diminished so that it takes about 1 hour to pass in the second mole; even at this slow rate, there is considerable fuming at the exit. After all the boron trifluoride has been introduced, the mixture is allowed to stand in the cooling bath under a slow stream of nitrogen for 1.5 hours. The mixture is swirled, and the suspended product is separated from the supernatant liquid by means of a medium-porosity, sintered-glass Buchner funnel. Note that since free hydrogen fluoride is no longer present, filtration can be carried out with glass or porcelain equipment.
The gooey solid remaining in the flask is transferred to the funnel with the aid of two 50-ml. portions of nitromethane. The solid on the funnel, nitronium tetrafluoroborate, is washed successively with two 100-ml. portions of nitromethane and two 100-ml. portions of methylene chloride. In order to protect the salt from atmospheric moisture during the washing procedure, suction is always stopped while the salt is still moist. The moist salt is transferred to a round-bottomed flask and dried by evaporating the solvent. At the end of the procedure the flask can be gently heated to 40–50°C (Nitronium tetrafluoroborate is thermally stable up to 170°. Above this temperature it starts to dissociate into nitryl fluoride and boron trifluoride.) The yield of colorless nitronium tetrafluoroborate is 85–106 g. (64–80%) It is stored in a wide-mouthed polyolefin bottle with a screw cap. The edge of the cap is sealed with paraffin wax after it is screwed on. Nitronium tetrafluoroborate is very hygroscopic. It is stable as long as it is anhydrous, but it is decomposed by moisture, and all transfers should be in a dry box.
Nitronium tetrafluoroborate slowly attacks polyethylene and polypropylene, but apparatus made of these materials will last for several preparations of the salt.
The last part of the procedure can be used to purify nitronium tetrafluoroborate that has picked up water on standing. The impure salt is washed twice with nitromethane, twice with methylene chloride, and is dried under reduced pressure.
Making Boron Trifluoride BF3
Boron trifluoride is a very toxic gas, which readily reacts with water to form metaboric acid and Fluoroboric acid, which then can further hydrolyze if excess water is present. It is a strong fluoride ion abductor, meaning it will pull a fluorine atom from many covalent compounds to form the tetrafluoroborate anion (BF4-), while leaving a positively charged cation. However, boron trifluoride is not as powerful of an abductor as antimony pentafluoride, as demonstrated by its unreactivity towards trichlorofluoromethane.
Boron trifluoride may be prepared by heating a mixture of boric oxide and calcium fluoride with concentrated sulfuric acid. It may also be prepared by mixing 5 parts of potassium borofluoride (KBF4) with 1 part finely powdered boric oxide, then heating with concentrated sulfuric acid. The boron trifluoride, can be collected over mercury. Potassium borofluoride may be produced by heating together 2 parts boric acid, 5 parts CaF2, and 10 parts conc H2SO4. The liquid is then cooled and filtered, and a solution of a potassium salt is added. Potassium borofluoride precipitates out, and may then be recrystallized from hot water. By this method it can be prepared as anhydrous hexagonal crystals. If it is prepared instead from hydrofluoric acid, boric acid, and K2CO3, a gelatinous mass forms instead, which however forms cubic octahedral and cubic dodecahedral crystals when heated to 100degC. Boron trifluoride also results from heating a mixture of boric oxide and calcium fluoride to a white heat in an iron pipe. Heating solid borofluorides to red heat, boron trifluoride is evolved, leaving behind metal fluorides.
Comments
SOMEONE MOVE THIS GEM TO CMS!
I should probably note that you added a space to the end of that URL, making it look odd. Maybe you should edit this before posting the link anywhere :thumbsup:
Saving this for later use, OP, like you recommended. Good idea!
Fixed