136 Synthetic Routes to AromaticC-Nitro Compounds
Olah and Lin^47 reported obtaining pure TNB (2) in 50 % yield from the nitration ofm-
dinitrobenzene (32) with nitronium tetrafluoroborate in fluorosulfuric acid at 150◦C; higher
yields of TNB can be obtained by reducing reaction time but the product then contains some
unreactedm-dinitrobenzene. A solution of dinitrogen pentoxide in sulfuric acid at 160◦Cis
also reported to effect the conversion ofm-dinitrobenzene to TNB.^48 TNB is rarely prepared
via these routes and is best obtained from TNT via an indirect route (Section 4.9).
4.3.2.6 Halobenzenes
Halogen substituents withdraw electron density from the aromatic nucleus but directo/p-
through resonance effects. The result is that halobenzenes undergo nitration with more dif-
ficulty relative to benzene. The nitration of chlorobenzene with strong mixed acid gives a
mixture of 2,4- and 2,6-isomeric dinitrochlorobenzenes in which the former predominates.^49
The nitration of 2,4-dinitrochlorobenzene to 2,4,6-trinitrochlorobenzene (picryl chloride) re-
quires an excess of fuming nitric acid in oleum at elevated temperature.^50 ,^51 Both are useful
for the synthesis of other polynitroarylene explosives but only 2,4-dinitrochlorobenzene finds
industrial importance (Sections 4.8.1.2 and 4.8.1.3).
ClClClClClClO 2 N NO 2 O 2 NNO 2NH 2H 2 N NH 2NO 2(^33) NO 2
34 14
(TATB)
oleum,
fuming HNO 3 NH 3 , PhCH 3
150 °C
Figure 4.11
1,3-Dichloro-2,4,6-trinitrobenzene and 1,3,5-trichloro-2,4,6-trinitrobenzene (34) are pro-
duced on an industrial scale for the synthesis of the thermally stable explosives 1,3-diamino-
2,4,6-trinitrobenzene (DATB) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) (14) respec-
tively. The nitration of both 1,3-dichlorobenzene^52 and 1,3,5-trichlorobenzene^53 (33) requires
very harsh conditions, the latter requiring an excess of fuming nitric acid and oleum at 150◦C
for 2.5 hours to yield a mixture containing the required 1,3,5-trichloro-2,4,6-trinitrobenzene
(34) (89 %) and 11 % of trichloro- and tetrachloro-dinitrobenzene impurities. These impurities
need separation before amminolysis to TATB (14) is conducted.^53 The nitration of 1,3,5-
trichloro-2,4-dinitrobenzene to 1,3,5-trichloro-2,4,6-trinitrobenzene using potassium nitrate
in sulfuric acid has been reported.^54 TATB has also been synthesized from the amminolysis^55
of 1,3,5-trifluoro-2,4,6-trinitrobenzene, but the synthesis of the latter, in two steps^56 from 1,3,5-
trifluoro-2-nitrobenzene, also requires harsh nitrating conditions and the yield is low (∼43 %).
4.3.2.7 Other substrates
The successive nitration of naphthalene allows the introduction of four nitro groups. Nitration
of naphthalene with concentrated nitric acid mainly yields 1-nitronaphthalene and a small
amount of 2-nitronaphthalene.^7 Nitration of pure 1-nitronaphthalene with mixed acid yields