ammonium dinitramide

This section is under construction, some of the details may not be accurate at this time
 
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.
 
 

Ammonium dinitramide (ADN) crystallizes as yellowish to white needles. The solid crystals have a density of 1.885 g/cm3, compared to 1.950 of ammonium perchlorate. The salt is hygroscopic., meaning it absorbs moisture from the air. ADN melts at 93degC before decomposing, although it is not thermally stable at elevated temperatures.  Even at 60degC there is noticeable degredation. ADN is somewhat photosensitive and should be stored away from light. One method of stabilization of ADN is to incorporate a very small quantity of hexamine during crystallization, which reduces the rate of degradation by nearly two thirds.

Energy of formation: -125.3 kJ/g  (compared to -238.1 for NH4ClO4)

Volume of Gases from detonation:  1084 liters/kg

Impact Sensitivity:  3-5  Nm         Friction Sensitivity:  64 N

Detonation Velocity:  about 7 km/sec

 For rocket Isp values, see: http://docs.google.com/viewer?a=v&q=cache:7kheIwxd0BkJ:wydawnictwa.ipo.waw.pl/cejem/1%25202011/Lempert.pdf+ADN+Isp+aluminum&hl=en&gl=us&pid=bl&srcid=ADGEESiMO8jfJy_lefs4uj1HI1lD4TuwpkyNb1l597w-NMiPJpLjNcHswpNUAnH5ZuGk1i3os-GKZY2ZzIe4F7MwtZO6Y5-qf3FKNqvOcKjBmQjvnvPPzIV7OhxNELcT7zCq8CUA9ENg&sig=AHIEtbRk4w8617SWcjEboT_oIJFqdLgC4w

The addition of guanylurea to dintramidic acid, which has been prepared in mixed acids immediately prior, results in the precipitation of guanylurea dinitramide out of solution. The compound is very resistant to impact and burns with a relatively cool flame, such that, when burned in a cardboard tube, it almost does not even leave any scorch marks on the outside. Guanylurea dinitramide does not melt, but decomposes at 205degC. NH2CONHC(NH2)NH2[+] [-]N(NO2)2

 
 
Preparation

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.

 

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.

 

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!)

 
Comments