urbaf2

NITRO DERIVATIVES OF ANILINE 557

had been applied for a long time as a commercial method of preparation of o- and

p- nitroanilines and was investigated by a number of authors including Beilstein
and Kurbatov [3] and Holleman [4]. The mononitation of acetanilide can be
effected even with 80% nitric acid.
Walker and Zincke [5] found that o- and p- nitroanilines could be obtained by
heating corresponding bromonitro derivatives of benzene with ammonia under
elevated pressure. The high yield of the reaction was due to the enhanced reactivity
of Br in the presence of the nitro group. The reaction has been utilized for the com-
mercial preparation of o- and p- nitroanilines. Ortho- or p- chloronitrobenzenes
are used as starting material.
Meta- nitroaniline was first prepared by Muspratt and A. W. Hofmann [6]
in 1846, by the reduction of m- dinitrobenzene with ammonium sulphide. Nowadays
with sodium sulphide used as reducing agent, this method is applied for the commer-
cial production of m- nitroaniline.
Nitroanilines may also be obtained by direct nitration of aniline (Bruns [7]),
provided that a solution of aniline sulphate in sulphuric acid is prepared first, and
then carefully introduced into a mixture of nitric acid with concentrated sulphuric
acid. A condition necessary for success is that the reaction temperature must
not exceed 0°C.
Among the three isomeric nitroanilines only m- nitroaniline was of any impor-
tance in explosives technology, being a starting material for the preparation of
tetranitroaniline.

DINITRO DERIVATIVES OF ANILINE

From among a number of dinitroaniline isomers known, only the 2,4- and

3,5-isomers (m. p. 187°C and 161°C respectively) are of importance from the point

of view of explosives chemistry:

2,4-Dinitroaniline forms yellow needles, difficult to dissolve in cold alcohol.

The compound was obtained by Rudnev [8] by vigorous nitration of acetanilide

to 2,4-dinitroacetanilide with an almost anhydrous nitrating agent, followed by

hydrolysis of the product.

Nowadays 2,4-dinitroaniline is prepared on a large scale by treating chloro-

dinitrobenzene with ammonia. The method was first reported by Engelhardt and
Lachinov [9] in 1870. Heating 2,4-dinitrophenol with an excess of urea at 208°C