urbaf2

NITRO DERIVATIVES OF BENZENE^243

Clearly, higher temperatures enhance the formation of the o-isomer at the

expense of the m- isomer. The presence of sulphuric acid in the nitrating mixture

results in a slight increase of the quantity of m- isomer formed and a corresponding

decrease in the production of the o- isomer.

TABLE 38

RESULTS OF THE NITRATION OF NITROBENZENE TO DINITROBENZENE UNDER

VARIOUS CONDITIONS

Nitrating agent

Temperature Isomer content, %

ºC meta ortho para

Nitric acid^0 93.2 6.4 0.5

30 90.9 8.1 1.0

Nitric and sulphuric 0 93.9 4.8 1.7

(^40) 91.8 6.8 1.4
Wyler [32] has carried out a vast amount of work on the nitration of benzene.
He found that in the nitration of benzene or nitrobenzene on an industrial scale,
a product was obtained containing up to 12% of the o- and p- isomers. This was
contrary to the generally held opinion that dinitrobenzene contains only 1% of
o- and 3% of p- dinitrobenzene.
Wyler proved by a number of experiments with the nitration of nitrobenzene
to dinitrobenzene, that the content of the o- and p- isomers in the product may
vary from 5 to 15%, depending on the reaction conditions. At a low temperature,
e.g. -17°C, equal amounts of the o- and p- isomers were formed, while higher
temperatures favoured the formation of the o- isomer, this being on the whole in
agreement with the earlier observations by Holleman and de Bruyn [31].
The results obtained by Wyler are shown in Table 39.
TABLE 39
RESULTS OF THE NITRATION OF NITROBENZENE UNDER VARIOUS CONDITIONS (WYLER)
Nitrating mixture
Composition of the
Nitration Weight ofSulphuric acid Nitric acid Period of product
tempera-
nitroben-
nitration
m.p.
ture, °C
zene Concen- Concen- ºC
g g tration g tration hr
% %
meta ortho para
-17
to -10 24.6 150 105 25 96 4.00 86.9 95.1 2.5 2.4
-5 -5 ,, ,, ,, ,, 2.00 86.8 94.7 3.5 1.8
25-29 ,, ,, ,, ,, ,, 1.75 85.0 92.6 5.0 2.4
65-69 ,, 500 100 250 ,, 1.5 83.0 89.7 7.7 3.0
65-75 ,, (^9009828488) 1.5 82.1 89.2 8.7 2.1
90-100 ,, ,, ,, ,, ,, 1.50 80.0 87.0 11.8 1.2
108-113 ,, ,, ,, ,, ,, 1.25 81.2 87.6 10.2 2.2
124-129 ,, ,, ,, ,, ,, 0.75 79.9 85.7 13.9 0.4