Organic Chemistry of Explosives

Energetic groups 285

NO 2

N

NO 2

147

Figure 6.45

Many studies into the dinitramide anion (147) have looked at the effect the counterion has on

physical properties. The ammonium, alkali metal, guanidinium, biguanidinium, aminoguani-

dinium, hydroxylammonium, 1,2-ethanediammonium and tetraammonium-1,2,4,7-cubane

salts of dinitramide have been prepared. Various metal salts of dinitramide are conveniently pre-

pared by ion exchange of the cesium or ammonium salts on polymer resins. TheN-guanylurea

salt of dinitramide, known as FOX-12, has been prepared from the addition of an aqueous

solution of ammonium dinitramide to the sulfate salt of guanylurea; the low solubility of

FOX-12 in cold water leading to its precipitation in 81 % yield.^74 FOX-12 is a very insensitive

explosive with potential for use as an ingredient in energetic propellants, or for use in insensi-

tive explosive munitions. The synthesis of materials like FOX-12 reflects the increased need

for insensitive explosives and propellants for modern applications. Although nitrocellulose–

nitroglycerine double-base propellants are still widely used for military applications, most

exhibit a high sensitivity to shock or impact which can sometimes lead to premature explosion.

The dinitramide ion is stable in both acidic and basic solutions between pH 1–15 at room

temperature but is slowly decomposed in the presence of strong concentrated acid. In contrast

to alkylN,N-dinitramines (Section 6.11.2) where the central nitrogen atom is highly electron

deficient, the dinitramide anion has its negative charge delocalized over both nitrogen and

oxygen atoms with the consequence that the N–N bonds are less susceptible to rupture. How-

ever, the dinitramide anion is not as stable as the nitrate anion; ammonium dinitramide melts

at 92◦C and decomposition starts at 130◦C.

Me 3 Si

N

NO 2

NO 2

Cs +Me 3 SiF + C 2 H 4

CsF

50 %

148

NO 2

N

NO 2

149

Figure 6.46

Numerous synthetic routes to the dinitramide anion have been reported.^75 Cesium

dinitramide (149) has been synthesized via the fluoride-catalyzedβ-elimination of 1-(N,N-

dinitramino)-2-trimethylsilylethane (148) with cesium fluoride; the latter prepared by treating

2-(trimethylsilyl)ethyl isocyanate with a solution of nitronium tetrafluoroborate and pure nitric

acid in acetonitrile.^75

EtO N

NO 2

O

NH 4

EtO N

NO 2

O

NO 2

NH 3 (gas)

NH 4 N

NO 2

NO 2

N 2 O 5 , CH 2 Cl 2

150

151 152

50 % (2 steps)

Figure 6.47