558 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES(Kym [10]) is another convenient method of preparation of 2,4-dinitroaniline.
Further nitration of 2,4-dinitroaniline leads to 2,4,6-trinitroaniline (picramide).
3,5-Dinitroaniline is usually obtained from 1,3,5-trinitrobenzene by reduction
of a nitro group with sodium hydrosulphide. It may be used as starting material
for the preparation of pentanitroaniline.
2,4-Dinitroaniline has weak explosive properties of the order of m- dinitro-
benzene. However, its sensitivity to impact, according to Wöhler and Wenzelberg
[10] is considerably higher than that of dinitrobenzene and similar to that of
TNT.
The manufacturing process applied for the production of 2,4-dinitroaniIine
at I. G. Höchst was as follows:
To 1700 1. of water 600 kg of chlorodinitrobenzene (m. p. not below 50°C) are
added while stirring, followed by 530 1. (480 kg) of 26.5% aqueous ammonia.
The whole is kept at 70°C for 2 hr. When the reaction has started the steam flow
must be stopped for a while since the temperature rises spontaneously to 115-
120°C (within 152 hr) due to the heat of the reaction. The pressure in the reactor
rises to 2 atm. After the temperature has become constant, steam is passed again
to keep the reactor contents at this temperature for another 4 hr. The temperature
should not exceed 130°C.
Then the reaction mixture is cooled while stirring, the precipitated product
is filtered off on a stoneware filter, washed with water until neutral and dried in
a shelf drier at 50°C for 12-16 hr. The product is obtained in almost theoretical
yield.
TRINITROANILINE (PICRAMIDE)
Picramide or 2,4,6-trinitroaniline (m. p. 190°C) forms deep yellow crystals,
difficult to dissolve in alcohol and ether but easily soluble in hot acetone, benzene
and ethyl acetate.
The compound was first obtained by treating picryl chloride (Pisani [12]) ortrinitroanisole with ammonia (Salkowski [13]). Later Witt and Witte [14] obtained
it by the nitration of o- or p- nitroacetanilide in oleum solution. For the nitration
a solution of KNO 3 in concentrated sulphuric acid was used. Spencer and Wright [15]
applied Kym’s method [lo] for the preparation of picramide, heating picric
acid with urea at 173°C for 36 hr. The yield obtained was about 90% of the
theoretical.