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PREPARATION OF MONONITROTOLUENES

In the nitration of toluene all three isomers are formed, the o- isomer being

the predominant product. The proportion of isomers formed depends to some
extent on the nitration temperature.

It was Pictet [7] who first observed, in 1893, that when nitrating toluene with
a mixture of nitric and sulphuric acids at -5°C, relatively more p- isomer could

be obtained than at 0°C.
Hollernan and Arend [8] observed the following relationship between the com-
position of the product of mononitration of toluene and the temperature (Table 48).

TABLE 48

RELATIONSHIP BETWEEN THE COMPOSITION OF THE MONONITRATION PRODUCT OF TOLUENE

AND THE TEMPERATURE

Composition of the product

Temperature

°C o- isomer

content, %

p- isomer m- isomer

-30 55.6 41.7 2.7

0 56.0 40.9 3.1

+30 56.9 39.9 3.2

+60 57.5 38.5 4.0

W. W. Jones and Russel [9] determined experimentally the rate of nitration

of toluene at 0°C and 30°C. Then they calculated the relative values of the A co-

efficient in the well known Arrhenius formula applying the conclusions of Brad-

field and B. Jones (p. 65) derived from the formula:

Ao=2.90 Am

Ao=2.70 Am

From this they calculated the compositions of the products obtained by mono-

nitration of toluene at -30°C and +60°C, as well as the differences in the activa-

tion energies :

Em-Eo=917 cal/mole/degree

Em-Ep=1103 cal/mole/degree

From these data the following rule can be derived: a lower nitration tem-

perature causes an increase of the p- nitrotoluene content in the product at the

cost of the o- and m- isomers.

Orlova [2a] gave similar figures:

at 30°C the proportion of m- nitrotoluene was 4.6%

at 55°C , , , , , 5.3%

at 70°C , , , , , 7.5%

The composition of the nitrating mixture also has an influence on the compo-

sition of mononitrotoluene. The proportion of m- nitrotoluene is reduced by an

NITRO DERIVATIVES OF TOLUENE^271