Organic Chemistry of Explosives

The nitrolysis of hexamine 247

5.15.1.6 Reaction of hexamine with dinitrogen pentoxide

The nitrolysis of hexamine with 40 equivalents of a 25 % solution of dinitrogen pentoxide in

absolute nitric acid in carbon tetrachloride at− 20 ◦C is reported to give a 57 % yield of RDX.

The product is free from HMX as determined by NMR (≥95 % pure).^116

5.15.1.7 Nitrosation–oxidation/nitrolysis of hexamine

N

NN

NO 2

O 2 N NO 2

N

N

NO

NOON

(CH 2 ) 6 N 4

104

109 3

HCl (aq), NaNO 2

pH 1, 50 %

99 % HNO 3 ,

30 % H 2 O 2 , - 40°C

N 74 %

Figure 5.105

The presence of HMX as an impurity in RDX is not a problem when the product is used

as an explosive. However, the need for an analytical sample of RDX makes other more in-

direct methods feasible. One such method involves the oxidation of 1,3,5-trinitroso-1,3,5-

triazacyclohexane (109) (‘R-salt’) with a mixture of hydrogen peroxide in nitric acid at sub-

ambient temperature and yields analytical pure RDX (74 %) free from HMX.^115 The same

conversion has been reported in 32 % yield with three equivalents of a 25 % solution of dini-

trogen pentoxide in absolute nitric acid.^116 1,3,5-Trinitroso-1,3,5-triazacyclohexane (109) is

conveniently prepared from the reaction of hexamine with nitrous acid at high acidity.^205

1,3,5-Trinitroso-1,3,5-triazacyclohexane is itself a powerful explosive but has a low chemical

stability.

5.15.1.8 Nitrolysis of 1,3,5-triacyl-1,3,5-triazacyclohexanes

The acetolysis of hexamine has proven a diverse route to cyclic polyamides. 1,3,5-Triacetyl-

1,3,5-triazacyclohexane (TRAT) has been synthesized in 63 % yield by heating hexamine with

acetic anhydride at 98◦C.^206 Analogous acyl derivatives are prepared by heating with other

acid anhydrides.^206

While the present industrial synthesis of RDX via the Bachmann process has many faults, it

is high yielding and would be difficult to match by an alternative synthesis. Even so, Gilbert and

co-workers^97 reported on a study investigating the nitrolysis of a series of 1,3,5-trisubstituted-

1,3,5-triazacyclohexanes for the preparation of RDX. In the series, which includes sulfon-

amides, amides and carbamates, only in the cases where R=alkanoyl (acylamines) was

efficient nitrolysis to RDX observed. These reactions are discussed in Section 5.6.1.1 and

illustrated in Table 5.4.

5.15.2 The synthesis of HMX

1,3,5,7-Tetranitro-1,3,5,7-tetraazacyclooctane (4), commonly known as Octogen or HMX

(high melting explosive), is the most powerful military explosive in current use. However, the