urbaf2

-_____. ~- - 1

NITRO DERIVATIVES OF TOLUENE^285

PREPARATION OF DINITROTOLUENES

The principal reaction products in the nitration of toluene are the isomers:
2,4- formed from o- and p- nitrotoluenes, and 2,6- formed from o- nitrotoluene.

From m- nitrotoluene the 2.3-, 3,4- and 3,6-isomers are formed. The possibility of

the formation of the 3,5-isomer in the direct nitration of m- nitrotoluene has not

been definitely proved.
Dinitrotoluene (2,4-) was first obtained by Beilstein and Kuhlberg [21] in 1870.

However, it may be that “dinitrobenzene”, m.p. 71°C obtained in 1841 by St.

Claire Deville [25] by the nitration of “nitrobenzene” prepared from light oil, was

in fact dinitrotoluene. As Rosensriel [26] found in 1872 p- nitrotoluene yields only

one product of dinitration, viz. the 2,4-isomer, while o- nitrotoluene gives in addi-

tion another isomer, the structure of which he did not determine.
The first indication of the existence of the other dinitrotoluene isomers can
be found in the Limpricht’s work [27]. He was able to isolate from the nitration

products the 3,6-isomer, besides the 2,4- and 2,6-isomers. In 1903 Zaloziecki [28]

nitrated the aromatic fraction of Galicia oil and isolated the 2,4- and 3,6-nitro-

toluenes.

Beilstein and Kuhlberg nitrated the m- nitrotoluene in 1873 and obtained the

3,4-isomer.

The data were confirmed by Häussermann and Grell [29] in 1894. They stated

that besides the isomers already mentioned, the 3,5-isomer was also isolated. Sev-

eral authors questioned the presence of the latter isomer in the nitration products.

For example, Sirks [30] reporttd that nitration of m- nitrotoluene resulted in the

formation of the 3,4-, 2,3-, and 3,6-isomers, but not the 3,5-isomer.

Gibson, Duckham and Fairbairn [13] have carried out more detailed studies,

in which they established that the following proportions of isomers are formed

in the nitration of various mononitrotoluenes (Table 58):

TABLE 58

NITRATION OF NITROTOLUENE ISOMERS

Dinitrotoluene isomers, content %

Substance being nitrated

2,4- 2,6- 3,4- 2,3- 3.6-

o- Nitrotoluene^67 33 - -

p- Nitrotoluene 100 -- - -

m- Nitrotoluene - - 55 25 20

De Beule [31] carried out the most extensive study of nitration of m- nitro-

toluene. He found the product was composed of 54.6% of 3,4-dinitrotoluene, 30.6%

of 2,3-dinitrotoluene, 13.0% of 2,5-dinitrotoluene, and 1.8% of 2,5-dinitrotoluene.

Thus he confirmed the formation of 3,5-isomer.