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90 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

CH 3 -CH 3 + HNO 3 -> -> H 2 O + C 2 H 5 NO 2 (15)

The nitration theory, which assumes that a free radical takes part, seems to

be more probable than the addition theory and is in better agreement with the

experimental data. An interesting piece of evidence for the participation of free

radicals in the reaction was given by McCleary and Degering [36], who obtained

a mixture of nitroethane and ethyl nitrate when nitrating tetraethyl lead with nitric

acid in an atmosphere of CO 2 , at 150°C. It is probable that the reaction proceeds

as follows:

(C 2 H 5 ) 4 Pb -> Pb + 4C 2 H 5.

C 2 H 5. + HONO 2 -> C 2 H 5 NO 2 + OH.

(16)

C 2 H 5. + OH. -> C 2 H 5 OH

C 2 H 5 OH + HONO 2 -> C 2 H 5 ONO 2 + H 2 O

NITROGEN DIOXIDE

As is well known, nitrogen dioxide exists as the dimer N 2 O 4 , at low temperatures,

and as the monomer, NO 2 , at high temperatures. Its boiling point is 21°C, and

its density at 0°C d = 1.49 g/cm

3

.

On the basis of the observation that the addition of nitrogen dioxide to com-

pounds with double bonds yields not only nitro compounds, but nitrous acid esters

as well (p. 99). Schaarschmidt [38a,39,40] expressed the view that nitrogen

dioxide exists in three forms which are in equilibrium. This may be represented in

modern symbols in the following way:

(a) (b) (c)

the equilibrium being shifted towards the (c) form.

More recent thermochemical studies (Giauque and Kemp [41]), and spectral

work (Millen [42]), as well as determination of the dielectric constant (Addison
and Lewis [43]), indicate that formula (b) seems to be the most probable. Formula

(d) is possible, but less probable.