Polynitroarylenes as explosives 127as explosives was related to the availability of the starting aromatic compounds and their isola-
tion from coal tar. The advent of the modern petrochemical industry means that availability of
many aromatic chemicals is no longer a problem. However, the use of many polynitroarylenes
as explosives is confined to history because of their moderate performance.
NHCNHONO 2NO 2NO 2 2 N NHONO 2NO 2NO 2O 2 NO 2 NSNO 2 O 2 NNO 22 O 2 NNO(NO 2 ) 2 O 2 NO 2 NO 2 NO 2 NO 2 N11
2,2',4,4',6,6'-hexanitrocarbanilide12
2,2',4,4',6,6'-hexanitrodiphenylamine
(hexyl)9
trinitronaphthalene 102,2',4,4',6,6'-hexanitrodiphenylsulfideFigure 4.22,4,6-Trinitrophenol (4), commonly known as picric acid (VOD∼7350 m/s,d= 1. 71
g/cm^3 ), was once used as a military explosive although its highly acidic nature enables it to
readily corrode metals. This kind of reaction has led to many fatal accidents, a consequence of
some metal picrates being very sensitive primary explosives. The lead salt of picric acid is a
dangerous explosive and should be avoided at all cost. In contrast, the ammonium (Explosive D,
VOD∼7050 m/s,d= 1 .60 g/cm^3 ) and guanidine salts of picric acid are unusually insensitive
to impact and have been used in armour piercing munitions.
2,4,6-Trinitroresorcinol (5) (styphnic acid) has also seen limited use as an explosive because
of its acidic properties and the relatively high cost of resorcinol. However, the lead salt of
styphnic acid has found use as a primary explosive in detonators and primers.
The acidity of polynitrophenols is a direct consequence of the negative inductive effect
of the nitro groups. This has implications for other polynitroarylenes as practical explosives.
2,4,6-Trinitroanisole (7), 2,4,6-trinitrophenetole (8), 2,4,6-trinitroaniline (picramide) and other
2,4,6-trinitrophenyl (picryl) compounds containing potential leaving groups undergo slow
hydrolysis in the presence of water/moisture to generate picric acid or other polynitrophenols
which can attack metal, and so, present a real risk when used in munitions destined for long-term
storage.
This powerful inductive effect is seen in highly nitrated polynitroarylenes. Thus, benzene
and its substituted derivatives containing four, five or six nitro groups on the same ring i.e. one
or more nitro groups in ametaposition, are all chemically unstable and readily lose a nitro group
on hydrolysis or in similar nucleophilic reactions. Many highly nitrated polynitroarylenes are
powerful explosives but are prevented from being practical explosives because of their poor
chemical stability. These issues of chemical stability are discussed more fully in Sections 4.8.2
and 4.8.3.