Organic Chemistry of Explosives

252 Synthetic Routes toN-Nitro

5.15.3.2 Effect of acidity and the presence of ammonium nitrate on the nitrolysis

of hexamine

Bachmann and co-workers^196 noted that hexamine can undergo two major types of cleavage,

leading to the formation of compounds containing either three- or four-amino nitrogen atoms.

Bachmann and co-workers^196 also noted that the products obtained from the nitrolysis of

hexamine under the KA-process are dependent on the acidity and/or the activity of the nitrating

agent. Under conditions of high acidity it was noted that RDX and the linear nitramine (247),

with its three amino nitrogens, are the major products of the nitrolysis. In comparison, under

conditions of low acidity, HMX and its linear nitramine analogue (248), with its four amino

nitrogens, are the main products of nitrolysis. Bachmann and co-workers^196 also observed that

the nitrolysis of hexamine with acetic anhydride and nitric acid in the presence of ammonium

nitrate greatly favours the formation of the cyclic nitramines RDX and HMX, whereas in the

absence of ammonium nitrate the linear nitramines (247) and (248) are favoured.

OAc

248

OAc

NO 2 NO 2 NO 2

AcO

247

NNN

NO 2 NO 2 NO 2

AcO N

NO 2

NNN

Figure 5.110

The above observations allow the selective formation of RDX, HMX or the two linear

nitramines (247) and (248) by choosing the right reaction conditions. For the synthesis of the

linear nitramine (247), with its three amino nitrogens, we would need high reaction acidity,

but in the absence of ammonium nitrate. These conditions are achieved by adding a solution

of hexamine in acetic acid to a solution of nitric acid in acetic anhydride and this leads to the

isolation of (247) in 51 % yield. Bachmann and co-workers^196 also noted that (247) was formed

if the hexamine nitrolysis reaction was conducted at 0◦C even in the presence of ammonium

nitrate. This result is because ammonium nitrate is essentially insoluble in the nitrolysis mixture

at this temperature and, hence, the reaction is essentially between the hexamine and nitric acid–

acetic anhydride. If we desire to form linear nitramine (248) the absence of ammonium nitrate

should be coupled with low acidity. These conditions are satisfied by the simultaneous addition

of a solution of hexamine in acetic acid and a solution of nitric acid in acetic anhydride, into

a reactor vessel containing acetic acid.

5.15.4 Other nitramine products from the nitrolysis of hexamine

5.15.4.1 The chemistry of DPT (239)

The chemistry of 1,5-dinitroendomethylene-1,3,5,7-tetraazacyclooctane (239) (DPT) is inter-

esting in the context of the nitramine products which can be obtained from its nitrolysis under

different reaction conditions. The nitrolysis of DPT (239) with acetic anhydride–nitric acid

mixtures in the presence of ammonium nitrate is an important route to HMX (4) and this

has been discussed in Section 5.15.2. The nitrolysis of DPT (239) in the absence of ammo-

nium nitrate leads to the formation of 1,9-diacetoxy-2,4,6,8-tetranitro-2,4,6,8-tetraazanonane

(248);^189 the latter has found use in the synthesis of energetic polymers.