Nitration 137NO 2 NO 2 NO 2 NO 2NO 2+++(1,5-) (1,8-)NO 2 NO 2 NO 2NO 2
NO 2 (1,3,5-) NO 2 NO 2
(1,4,5-)NO 2NO 2
(1,3,8-)NO 2 NO 2 NO 2 NO 2O 2 N NO 2NO 2NO 2 NO 2NO 2
NO 2NO 2(1-)(1,3,6,8-)(1,4,5,8-)(1,3,5,8-)Figure 4.12 Nitration of 1-nitronaphthalene with mixed acid – Ref. 59a mixture of 1,5- and 1,8-isomers in an approximate 35:65 ratio depending on the nitrating
agent and conditions used.^57 ,^58 Further nitration of 1,5-dinitronaphthalene yields both 1,3,5-
and 1,4,5-trinitronaphthalenes, whereas 1,8-dinitronaphthalene predominantly yields 1,3,8-
trinitronaphthalene.^58 ,^59 Commercial trinitronaphthalene is thus largely a mixture of 1,3,5-,
1,4,5- and 1,3,8-isomers. In practice small amounts of other isomers are present and their ra-
tio, relative to the main isomers, is heavily dependent on temperature and nitrating agent used.^58
Introduction of a further nitro group requires concentrated sulfuric acid and fuming nitric acid
to yield a mixture of isomeric 1,3,5,8-, 1,3,6,8- and 1,4,5,8-tetranitronaphthalenes.^58 ,^59 Direct
nitration of 1-nitronaphthalene or dinitronaphthalenes to tetranitronaphthalenes requires an ex-
cess of strong mixed acid and increased temperature.^58 –^60 The most extensive study into naph-
thalene nitrations was conducted by Ward and co-workers who synthesized all ten possible iso-
mers of dinitronaphthalene and studied their nitration to tri- and tetra-nitronaphthalenes.^57 –^59
These ‘unnatural’ isomers were largely synthesized by diazotization of the corresponding
naphthylamines in the presence of excess nitrite anion and a copper salt (Section 4.6).^61 –^66
Some substrates like benzoic acid, benzaldehyde etc. are so deactivated that direct nitration
to their trinitro derivatives is not possible. Direct nitration of benzoic acid with excess fuming
nitric and concentrated sulfuric acids at a temperature of 145◦C for several hours results in
the formation of 3,5-dinitrobenzoic acid (54–58 %).^67 The use of oleum in such reactions can
significantly reduce the rate of nitration due to carbonyl protonation (see Section 4.3.3). Conse-
quently, indirect routes are used for the synthesis of polynitroarylenes like 2,4,6-trinitrobenzoic
acid and 2,4,6-trinitrobenzaldehyde (Section 4.9).
Exact experimental conditions including the composition of nitrating agent used for the
industrial synthesis of all common polynitroarylene explosives is given by Urba ́nski.13a