urbaf2

NITRATION AGENTS AND METHODS MORE RARELY USED 91

The stereo-structure, including bond distances and bond angles of vapour phase

NO 2 (Fig. 17), was investigated by Maxwell and Mosley [44] in 1940 by electron

FIG. 17. Bond distances and angles of nitrogen dioxide (Maxwell

and Mosley [44]).

FIG. 18. Bond distances and angles of dinitrogen tetroxide (Broadley

and Robertson [45]).

diffraction and the stereo-structure of solid N 2 O 4 (Fig. 18) was determined in 1949

by X-ray analysis by Broadley and J. M. Robertson [45].

The ability of N 2 O 4 to react in various ways suggested that the substance can

also undergo heterogeneous dissociation in various ways. Three modes of

ionization of N 2 O 4 in dilute solutions are known. In water NO 2 - and NO 3 - are

produced, in strong acids, such as sulphuric acid, NO+ and NO 2 + are formed,

and under other conditions intermediate ionization leads to formation of NO

+

and NO 3

• . Clusius and Vecchi [46] found, when dissolving tetramethylammonium

nitrate (CH 3 ) 4 N

+ 15

NO 3

• labelled with

15

N isotope in N 2 O 4 , that complete exchange

of the

15

N isotope took place according to the equation:

N 2 O 4 <-> NO+ + NO 3 - (17)

N 2 O 4 in nitric acid solutions dissociated in the same way, as Goulden and

Millen [47] found, when examining Raman spectra of such solutions.

Millen and Watson [48] confirmed this observation by examining the infra-red

spectra of the same solutions. Very recently Goulden, Lee and Millen [48a] examined

the electrical conductances of solutions of dinitrogen tetroxide in nitric acid and

came to the conclusion that N 2 O 4 is subjected to nearly complete ionization ac-

cording to eqn. (17).

There is no evidence that the heterolytic dissociation may have the form (18)

which was accepted in earlier days:

N 2 O 4 <-> NO 2 + + NO 2 - (18)