192 Synthetic Routes toN-Nitro
Nitrimines are a relatively minor group ofN-nitro compound. The nitro derivatives of
guanidine and related compounds are the most important examples of the nitrimine group.
Primary nitramines have acidic protons and are able to undergo condensation reactions
to form functionalized nitramines. These reactions are discussed in Section 5.13 because the
products have potential application as energetic polymer precursors or find use for the synthesis
of other explosives.
5.2 Nitramines, nitramides and nitrimines as explosives
The energetic nature of the N–NO 2 group means thatN-nitro-based explosives are some
of the most powerful explosives available and these have largely superseded aromaticC-nitro
compounds for military applications. Many nitramines exhibit high brisance and high chemical
stability in combination with a favourable low sensitivity to impact and friction compared to
nitrate ester explosives of similar power.
CH 3 NHNO 2
1
methylnitramineO 2 NHNNHNO 22
ethylenedinitramine
(EDNA)Figure 5.2The chemical properties of primary and secondary nitramines are important in relation to
their use as explosives. Primary nitramines contain acidic hydrogen in the form of−NHNO 2
and, consequently, in the presence of moisture, primary nitramines corrode metals and form
metal salts, some of which are primary explosives. This is one reason why powerful explosives
like methylnitramine (1) have not found practical use. Ethylenedinitramine (EDNA) (2) suffers
from similar problems but its high brisance (VOD∼8240 m/s,d= 1 .66 g/cm^3 ) and low
sensitivity to impact have seen it used for some applications.
In contrast, secondary nitramines have no acidic hydrogen and often exhibit a high chem-
ical stability in combination with acceptable thermal and impact sensitivity. Consequently,
secondary nitramines are often the explosives of choice for military use.
1,3,5-Trinitro-1,3,5-triazacyclohexane (RDX) (3) and 1,3,5,7-tetranitro-1,3,5,7-tetraazac-
yclooctane (HMX) (4) are the most important of the secondary nitramine explosives. RDX
exhibits both high brisance (VOD∼8440 m/s,d= 1 .70 g/cm^3 ) and stability, finding extensive
use as a military explosive in the form of compressed or cast mixtures with other explosives,
or in the form of PBXs (plastic bonded explosives) where it is incorporated into a polymer
matrix with added plasticizer. HMX (VOD∼9110 m/s,d= 1 .90 g/cm^3 ) exhibits higher per-
formance than RDX due to its higher density, but this is offset by its higher cost of production
compared to RDX. Consequently, HMX is restricted to military use, finding use in high per-
formance propellant and explosive formulations. Both RDX and HMX are discussed further in
Section 5.15.
Although RDX and HMX are adequate for military applications, they are by no means
perfect. The risk of premature detonation increases when such explosives are used in shells for
high calibre guns due to the higher ‘set-back’ force. Also of concern is the risk of catastrophic