Organic Chemistry of Explosives

Nitration 133

Phloroglucinol (25) is more susceptible to oxidation than both phenol and resorcinol. How-

ever, its direct nitration to 2,4,6-trinitrophloroglucinol (27) can be achieved by the slow addi-

tion of a nitrating agent composed of concentrated sulfuric acid and concentrated nitric acid

to a solution of phloroglucinol dihydrate in concentrated sulfuric acid between 0 and 10◦C

(72 %).^28 –^30 Acetylation of phloroglucinol (25) yields the triacetate (26) which moderates

reactivity but still allows the synthesis of 2,4,6-trinitrophloroglucinol (27) on treatment with

fuming nitric acid at 0◦C (53 %),^31 mixed acid at –10◦C (91 %),^30 or dinitrogen pentoxide

in sulfuric acid (92 %).^30 2,4,6-Trinitrophloroglucinol has also been obtained on treatment of

phloroglucinol with dinitrogen pentoxide in sulfuric acid (74 %)^30 and via the oxidation of

1,3,5-trinitrosophloroglucinol with 65 % nitric acid (70 %).^30 ,^32 2,4,6-Trinitrophloroglucinol

finds use in cap and percussion compositions and as a flash sensitizer in some detonators.^28

m-Cresol is more susceptible to oxidation than phenol due to additional activation from the

methyl group. This accounts for the lower yield of 2,4,6-trinitrocresol product on trinitration

with mixed acid or concentrated nitric acid. For such substrates the use of sulfonation prior

to nitration is essential. The di-nitration of 1-naphthol to 2,4-dinitro-1-naphthol also uses

a sulfonation–nitration strategy because of the substrate’s susceptibility to oxidation, prior

heating of 1-napthol with concentrated sulfuric acid forming 1-napthol-2,4-disulphonic acid.

Phenol ethers, like the parent phenols, are reactive substrates. Phenol ethers like anisole

and phenetole are readily nitrated to their picryl ethers, 2,4,6-trinitroanisole and 2,4,6-

trinitrophenetole respectively, on treatment with mixed acid composed of concentrated nitric

and sulfuric acids at 0◦C.^33 Such reactions are vigorous, prone to oxidative side-reactions,

and pose a considerable safety risk. The direct nitration of 2,4-dinitrophenol ethers, obtained

from the reaction of 2,4-dinitrochlorobenzene with alkoxides, provides a more practical route

to picryl ethers on an industrial scale.^33

4.3.2.2 Amines

Aromatic amines are exceptionally reactive to electrophilic nitration. Aniline is readily nitrated

to 2,4,6-trinitroaniline (picramide) with mixed acid using acetic acid as solvent. When excess

sulfuric acid is present, aniline is largely protonated, making nitration difficult and directing

the incoming nitro group to them-position to yieldm-nitroaniline. The sensitivity of aniline to

oxidative degradation and the formation of phenolic by-products in the presence of nitrous acid

means that other indirect routes to picramide have been reported,^34 including treating picryl

chloride with hydroxylamine,^35 and methylation of picric acid followed by treatment with

ammonia.^30 Picramide is also prepared from the nitration of eithero-orp-nitroacetanilides

using a solution of potassium nitrate in concentrated sulfuric acid,^36 the acetamino behaving

as a reactivity moderator and also protecting the amino group against oxidation. Picramide

has no use as an explosive but may find use for the future industrial synthesis of TATB via

vicarious nucleophilic amination (Section 4.8.4).^37

NH 2

NO 2

NO 2

NO 2

29

O 2 N

NH 2

NO 2

90 % HNO 3 ,

20 % oleum, 70–80 °C

65–70 %

28

Figure 4.8