Organic Chemistry of Explosives

The nitrolysis of hexamine 243

The phenol (237) can be synthesized via a Mannich condensation between phenol, formalde-

hyde and dimethylamine,^184 followed by nitration–nitrolysis of the product (236) with con-

centrated nitric acid.^185 The phenolic group of (237) is acidic, and so enables the formation of

metal salts which are very impact sensitive explosives.

5.15 The nitrolysis of hexamine

N

NN N

NN

N

NO 2

O 2 N NO 2

N

N

N

N

104

NO 2

O 2 N NO 2

O 2 N

3

(RDX)

4

(HMX)

Figure 5.98

The nitrolysis of hexamine (104) is one of the most complex and widely studied processes in

the history of energetic materials synthesis. There are twelve CH 2 –N bonds in hexamine (104)

which can undergo scission, and with nitrolysis occurring to varying extents, it is unsurprising

that many different compounds can be produced during these reactions. Many of the possible

compounds are transient intermediates or are too unstable for isolation, as in the case of many

linear methylol nitramines whose existence is known from their reactions in solution or from

the isolation of their acetyl or nitrate ester derivatives. With so many reaction routes available

during the nitrolysis of hexamine it may seem strange that the cyclic nitramines RDX (3) and

HMX (4) can be isolated in such high yields. The reason for this observation is that both RDX

and HMX are very chemically stable and by far the most stable compounds present under

the harsh conditions of the nitrolysis. If fact, studies have shown that various fragments from

the nitrolysis of hexamine can recombine to form either RDX or HMX and so provide a sink

for active methylene and nitrogen containing fragments. Linear methylol nitramines and their

derivatives are unstable under the nitrolysis conditions and at reaction temperatures of 80◦C

they can fragment into smaller molecules which are also capable of forming RDX or HMX.

The importance of cyclic nitramines as military explosives has meant that an enormous

amount of research has been conducted in this area. Only some of the rich array of products

and by-products obtainable from hexamine nitrolysis are discussed in this section. For mech-

anistic studies and detailed analysis of these reactions the primary research papers should be

consulted.^24 ,^186 −^197

5.15.1 The synthesis of RDX

1,3,5-Trinitro-1,3,5-triazacyclohexane (3), also known as Cyclonite, Hexogen, T4 or more

commonly as RDX (research department explosive), was first discovered by Henning^198 and is

the most important military explosive in modern day use. The high brisance exhibited by RDX,

its stability on storage and low sensitivity to impact and friction in comparison to many nitrate

ester explosives, makes it a desirable secondary high explosive. The use of RDX as a component