Post by Anders Hoveland on May 17, 2011 20:25:04 GMT -8
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.
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.