Organic Chemistry of Explosives

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Energetic Compounds 3:

N-Heterocycles

7.1 Introduction

Until the end of the First World War the main filling for mass ordnance was TNT and its

mixtures with ammonium nitrate known as Amatols. During this period improved methods for

the manufacture of RDX enabled its inclusion in munitions, usually in formulation with TNT

in the form of the Cyclotols. RDX and its mixtures are still the most widely used explosives

for military use.

RDX by any measure is a high performance explosive. However, rapid advances in war-

fare technology demand even higher performance materials coupled with low sensitivities to

impact, shock and friction. Most secondary high explosives in wide use today are vulnera-

ble to premature detonation when used in high demand applications such as the warheads of

high-speed guided missiles and high-calibre guns. The incorporation of such explosives into

a polymeric matrix (PBX) has been a common strategy to reduce sensitivity and this is gen-

erally successful. However, such explosives are still susceptible to detonation from the shock

of another explosive. The risk of catastrophic explosion in the magazine of a ship or similar

munitions storage areas cannot be ignored. Many countries have an ongoing research program

to find new energetic materials with a low vulnerability to accidental initiation. The intention

is to gradually phase out current explosives for insensitive high explosives (IHEs). Another

area of research involves finding and synthesizing thermally stable explosives. Such materials

have commercial value for applications involving high temperatures like the drilling of deep

oil wells and for the space programmes.

Many of the aforementioned properties are present in nitrogen heterocycles and these are

the discussion point of this chapter. Many of theN-heterocycles described in this chapter

have high percentages of nitrogen in their skeletal structure, and consequently, have excep-

tionally high heats of formation and are highly endothermic in nature. Such compounds are

classically energetic and release large amounts of energy on combustion and often exhibit

high performance. The high nitrogen content of these compounds often leads to a high crystal

density which is itself associated with increased performance. Research into this class of en-

ergetic materials is still strong and manyN-heterocycles have found specialized applications.

Unlike caged polynitropolycycloalkanes and polynitramines, manyN-heterocycles are fairly

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