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GENERAL INFORMATION ON NITRO COMPOUNDS 187

that the nitro group itself gives the Zerevitinov reaction, even when a compound

does not contain hydrogen at all, as for example, tetranitromethane, pentabromo-

nitrobenzene, etc.

According to several authors (e.g. Moureu [85], Bewad [86], Kharasch and

Reinmuth [70]), the Grignard reagent may react with nitro groups reducing

them to amino- or hydroxyamino groups (NHOH). However, this is not

the only way the Grignard reagent reacts with aromatic nitro compounds.

Thus Severin [71] has established that sym-trinitrobenzene reacts with mag-

nesium alkyl bromide to form a yellowish precipitate of an addition product

which, with aqueous acetic acid, gives colourless crystals of 1,3,5-tri-alkyl-

2,4,6-trinitrocyclohexane

R = C 2 H 5 (m. p. 276°C)

R = C 4 H 9 (m. p. 258°C)

Polarographic reduction of nitro compounds is a subject matter of a recent

monograph by Strading [87].

HETEROCYCLIC NITRO COMPOUNDS

Heterocyclic nitro compounds have no practical importance in the technology

of explosives, either because the raw materials are too expensive, or because it

is difficult to introduce the nitro group into them. For example, pyridine and its

homologues, the most easily obtainable heterocyclic compound, are nitrated only

with the greatest difficulty, and the most powerful nitrating agents give 3-nitro-

pyridine only in low yield (e.g. 6%) [89].

When nitrated in the gaseous phase with nitrogen dioxide at temperatures of

115-120°C, pyridine gives also 3-nitropyridine (Shorygin and Topchiyev [74])

in the same yield. See also Schofield [90].

Alkylpyridines (picolines, and especially lutidines) can be nitrated much more

readily, as Plazek [75] has shown. Introduction of the nitro group is greatly facil-

itated by the presence of the hydroxyl group in the pyridine ring. For example,

3-hydroxypyridine can be nitrated to 2-nitro-3-hydroxypyridine in good yield

(Plazek and Rodewald [76]). It may be further nitrated to the dinitro derivative.

From this, 3,5-dinitropyridine can be obtained (Plazek [77]).

It has been shown recently by den Hertog and Overhoff [78] that N-pyridine

oxide can readily be nitrated with a nitric and sulphuric acid mixture. 4-Nitro-

pyridine is formed in good yield-about 81%.