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NITRATION AGENTS, AND METHODS MORE RARELY USED^131

INTRODUCING THE NITRO GROUP BY OXIDATION

In addition to the nitration of phenols by substitution of sulpho groups (p. 130)

the method of nitrosation of phenols, followed by oxidation of the nitroso to the

nitro group has some practical application:

(101)

The method is used for those readily nitrated phenols (e.g. resorcinol), when less

nitro groups are to be introduced than is possible in the direct nitration (Kosta-

necki and Feinstein [205]).

Oxidation of diazo compounds may result in the formation of nitramines, for

example, phenylmtramine :

(102)

This is one of the reactions which were used to prove that nitramines are com-

pounds with the nitro group attached to the nitrogen atom.

A nitro group may also be introduced by the oxidation of oximes. For this,

salts of hypobromous acid are generally used. This method is sometimes applied

for the preparation of aliphatic nitro compounds. The reaction proceeds in

the following way (Forster [206], Cherkasova and Mehrikov [207], Iffland

et al. [208]):

(103)

Iffland and Criner [209] have improved the method. They obtained nitrocyclo-

hexanone from cyclohexanone in about 50% yield, using N-bromosuccinimide as

an oxidizing and brominating agent.

Introducing a nitro group by oxidation of a primary amino group. The method

of oxidizing a primary amino group to a nitro group is sometimes used commer-

cially. A nitroso compound is an intermediate product of the reaction and it can

generally be isolated :

-NH 2 -> -NO -> -NO 2

The oxidation is carried out by means of the so-called Caro's acid (H 2 SO 5 ), which

is prepared by reacting sulphuric acid with persulphuric acid salts, or by reacting

concentrated hydrogen peroxide with sulphuric acid.

In this way nitrosobenzene may be obtained from aniline, as has been shown

by Bambergcr and Tschirner [220]. Nitrosobenzene may then be oxidized to nitro-
benzene.
Page and Heasman [210] obtained 3,6- (or 2,5-) dinitrotoluene by reacting Caro’s

acid with 5-nitro-o-toluidine. Brady and Williams [211] used the same method