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NITRATION THEORIES 65

Similar results have been obtained in the nitration of chlorobenzene, as shown

in Table 4.

TABLE 4

Temperature, °C

Composition of the product

% ortho- % para-

0 30.1 69.9

-30 26.9 73.1

As for naphthalene, Pictet [56] found that nitration at temperatures from

-50 to -60°C mostly resulted in the formation of 1,5-dinitronaphthalene with

a certain amount of the 1,3-isomer, while at a temperature higher than room tem-

perature 1,5-dinitronaphthalene is formed along with l,8-isomer.

Bradfield and B. Jones [57] applied the Arrhenius equation, known from chemi-

cal kinetics, to the reaction of substituting various benzene derivatives by the

nitro group (or by chlorine) at different temperatures:

where for each isomer:

k - rate constant for the substitution reaction,

E - activation energy,

A - coefficient independent of temperature,

T - absolute temperature,

R - gas constant,

n - number of equivalent substitutions possible (for example, in the con-

version of a monosubstituted into an ortho-disubstituted derivative n = 2, into a

meta-disubstituted derivative, n = 2, and into the para-disubstituted derivative

n = 1).

The number of isomers formed in a substitution reaction at a given tempera-

ture may be calculated if the composition of the substitution product, obtained

at a different temperature is known. The equations have to be worked out for

each isomer, in which ko, Ao, Eo, km, Am, km, kp, Ap, Ep are the values, corre-

sponding to the ortho-, meta- and para- isomer respectively.

The procedure of Bradfield and B. Jones was applied later by W. W. Jones

and Russel [58] to their experiments on the nitration of toluene (their work will

be further discussed later on p. 274). The results they obtained established the

rule: a lower nitration temperature causes an increase in the quantity of para- nitro-

toluene formed and reduces the amounts of ortho- and meta- isomers.

The nature and composition of the nitrating agent distinctly affects the com-

position of the nitration products.

Noelting and Forel [59] stated that an increase in HNO 3 concentration in the

nitrating mixture increases the amount of para- nitro compound produced. Thus,