64 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVESkinetics will be considered from another viewpoint-that of the influence of
various substituents in promoting or inhibiting further substitution.
A great deal of research work has been carried out with the object of studying
the orientation of nitro groups introduced into an aromatic ring. The most ex-Group present
on the ringF
Cl
Br
I
CH 3
CH 2 Cl
CHC1 2
CCl 3
COOC 2 H 5
COOH
NO 2TABLE 2Composition of the product
% ortho- o/o meta-
12.4 trace
30.1 trace
37.6 trace
41.1 trace
58.8 4.4
40.9 4.2
23.3 38.8
6.8 64.5
28.3 68.4
18.5 80.2
6.4 93.2% para-
87.6
69.9
62.4
58.7
36.8
54.9
42.9
28.7
3.3
1.3
0.25tensive investigations are those by Holleman [49-55], who in the period 1895-1924
carried out numerous experiments and systematized the data obtained.
Holleman [55] gives the following data on the composition of the nitration
products obtained in the nitration of different monosubstituted benzene deriva-tives with mixtures of nitric and sulphuric acids (Table 2). As appears from the data
shown below, the substituent already present affects the orientation of the group
which is being introduced. It is evident that nitration can be influenced by the
steric factor. For exampl: tert.-butylbenzene is mainly nitrated in para (72.7%)
and to a much lesser extent in ortho (15.8%) positions (H. C. Brown and Nelson [88]).
TABLE 3Temperature, °CComposition of the product
% ortho- % para- % meta--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 4.0The influence of the nitration temperature on the orientation of a nitro group
is in certain cases rather marked. When nitrating toluene with a mixture of nitric
and sulphuric acids at -5°C, Pictet [56] observed that more para-isomer was
obtained than at the temperature of 0°C.
Holleman and Arend [49] gave more detailed data, showing the influence of
temperature on the composition of the product obtained in the mononitration of
toluene with a mixture of nitric and sulphuric acids (Table 3).