Organic Chemistry of Explosives

250 Synthetic Routes toN-Nitro

O 2 N

NO 2

99 % HNO 3

96 % H 2 SO 4

98 % HNO 3 ,

88 % PPA, 60 °C

or 98 % HNO 3 ,

P 2 O 5 , 50 °C

N

NN

N

Ac

Ac

N

NN

N

Ac

Ac

240

(DAPT)

80

(DADN)

N

NN

N

O 2 N NO 2

O 2 N NO 2

3

(HMX)

Figure 5.108

[3.3.1]nonane (DAPT) (240) can be prepared in yields above theoretical (119 % based on

hexamine) by slowly adding acetic anhydride to a slurry of hexamine, water and ammonium

acetate.^213 Further studies show that acetic anhydride can be replaced by ketene.^213 Gilbert and

co-workers^214 isolated 1,3,5,7-tetraacetyl-1,3,5,7-tetraazacyclooctane (TAT) (79) in 70 % yield

by heating DAPT (240) with acetic anhydride for 3 hours at 110◦C. Further improvement using

a mixture of acetyl chloride, acetic anhydride, acetic acid and sodium acetate gave yields of

TAT (79) between 75 and 90 %.^215 The direct preparation of TAT (79) from hexamine has also

been described.^216

The acetolysis of hexamine closely resembles that of hexamine nitrolysis. Accordingly,

acidity is of key importance, with high concentrations of acetic acid favouring the formation of

the 6-membered 1,3,5-triacetyl-1,3,5-triazacyclohexane (TRAT) and weakly acidic conditions

favouring the 8-membered 1,3,5,7-tetraacetyl-1,3,5,7-tetraazacyclooctane (TAT).^217

Gilbert and co-workers^214 conducted extensive studies into finding better routes to HMX.

The direct nitrolysis of TAT (79) with phosphorous pentoxide in nitric acid is reported to give

a 79 % yield of HMX. The same reaction with DAPT (240) is much lower yielding (maximum

11 %). However, a more satisfactory route is via the nitrolysis of the half-way intermediate, 1,5-

diacetyl-3,7-dinitro-1,3,5,7-tetraazacyclooctane (DADN) (80). DADN (80) can be prepared

from the nitrolysis of DAPT (240) or directly from hexamine. In the latter process, hexamine

is treated with aqueous ammonium acetate and acetic anhydride, and the resulting solution

of DAPT (240) added to a mixed acid composed of 99 % nitric acid and 96 % sulfuric acid,

a process giving DADN (80) in 95 % yield. Extensive studies were conducted into the best

conditions and reagents needed for DADN (80) nitrolysis, nitric acid–PPA (99 % yield, 100 %

purity) and nitric acid–phosphorous pentoxide (99 % yield, 100 % purity) proving the most

efficient. Other reagents gave poorer yields and include nitric acid–TFAA (82 %), nitrogen

pentoxide–nitric acid (82 %), nitric acid–sulfur trioxide (60 %) and neat nitric acid (44 %).

The synthesis of HMX via the nitrolysis of DADN (80) with dinitrogen pentoxide in nitric

acid is being utilized in the UK on pilot plant scale and is under development for large-scale

production in the US.^214 The synthesis is a three-stage process: (1) hexamine is reacted with

acetic anhydride and ammonium acetate to give DAPT (240), (2) mild nitration with mixed

acid and (3) more vigorous nitration to HMX with nitrogen pentoxide in nitric acid. The latter

reagent can be preparedin situby using a mixture of phosphorous pentoxide in nitric acid^218

or via the electrochemical oxidation^219 of nitric acid–dinitrogen tetroxide mixtures.

5.15.3 Effect of reaction conditions on the nitrolysis of hexamine

Reaction conditions such as temperature, concentration, reaction acidity, stoichiometry and

reactants used, together with their order of addition, all have a profound effect on the outcome