urbaf2

NITRATION AND NITRATING AGENTS 21

N 2 O 5 in the solution. The failure of Hantzsch to find an absorption maximum

in the solution of nitric acid in ether was, according to Jones and his co-workers,
due to the presence of N 2 O 5 in his acid. Indeed, these authors reported that solutions

of N 2 O 5 in nitric aciddo not show a maximum (Fig. 7).

FIG. 7. Ultra-violet absorption spectra of solutions of N 2 O 5 in anhy-

drous nitric acid. (R. N. Jones, Thorn, Lyne and E. G. Taylor [58]).

Jones expressed the view that the identification of “260 mμ chromogen” with

undissociated nitric acid molecule (Hantzsch’s pseudo-acid) is largely a specula-
tive hypothesis for which there is insufficient evidence. He suggested that the

260 mμ band is produced by the NO 2

+

ion or by the undissociated N 2 O 5 molecule.

The high intensity of this absorption may obliterate the weak absorption of the

nitrate ion at 302 mμ.

He summarized his views in the following system of equilibria:

Spasokukotskii [59] explained the results of these investigations in a similar

way. He believed that the absorption maximum at 265 mμ corresponds to the

nitronium ion NO 2 +,which is formed by a process of “self-ionization”:

3HNO 3 <-> NO 2 + + H 3 O+ + 2NO 3 - (34)