Nucleophilic aromatic substitution 167NNNNHHNNHO 2 N NO 2NO 2NO 2NO 2 O 2 N NO 2NO 2
H 2 NO 2 N
NH 2NH 2NH 2H 2 N NH 2NH 2ClClNNNClClCl120
(PL-1)+ 3- DMF, 90 °C, 90 %
- oleum, HNO 3 , 70 %
- NH 3 , acetone, 50 %
118 119Figure 4.48Agrawal and co-workers^248 synthesized 2,4,6-tris(3′,5′-diamino-2′,4′,6′-trinitrophenylamino)-
1,3,5-triazine (PL-1) (120) by condensing three equivalents of 3,5-dichloroaniline with cya-
nuric chloride, followed by nitration with fuming nitric acid in oleum and final chloro group
displacement with ammonia in acetone. PL-1 possesses a unique combination of moderate
heat resistance, high density and insensitivity to impact and friction. A large number of heat
resistant energetic materials based on heterocyclic rings are discussed in Chapter 7. The re-
search conducted on heat resistant explosives has been reviewed by Dunstan,^249 Urbanski,^250
Lu,^241 and more recently by Agrawal.^251
4.8.2 Nitro group displacement and the reactivity of polynitroarylenes
Nucleophiles can react with polynitroarylenes to displace one of the nitro groups. It is found
that nitro groups positionedo-orp-to each other are chemically unstable and are readily
displaced by a range of nucleophiles. Only nitro groups positionedm- to one another show
relatively high chemical stability. Such observations result from the electron-withdrawing nitro
group leading to a greater reduction in electron density ato- andp-positions relative tom-
positions. The more nitro groups present on the aromatic ring the greater the tendency is for
displacement with nucleophiles.
An unfortunate consequence of the high reactivity of some nitro groups is that many powerful
explosives are too chemically reactive for both commercial and military use. This is the case
with highly nitrated compounds containing four or more nitro groups per benzene ring. Some of
these compounds are illustrated below; chemically unstable nitro groups i.e. those positioned
o/p- to other nitro groups, are indicated by an asterisk.
NO 2NO 2NH 2
NO 2NO 2OHNO 2NO 2 NO 2NO 2O 2 N O 2 NO 2 N O 2 NNO 2 O 2 N NO 2 O 2 N NO 2 *
NO 2 NO 2
(^541213155)
Figure 4.49