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NITRATION AGENTS AND METHODS MORE RARELY USED 93

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As a result of nitrating phenol by means of N 2 O 4 at a low temperature, a mixture

of o- and p- nitrophenol was obtained.

The ability of nitrogen dioxide to form addition products with aromatic com-

pounds has been proved with polycycloketones. Thus, Lukin and Dashevskaya

[56] found that benzanthrone formed an addition product with two NO 2 mole-

cules. There is no doubt that the presence of carbonyl groups affects the ability

to form addition products just as it does in the addition of nitric acid (pp. 54-55).

It has been found recently that nitrogen dioxide forms addition products

with compounds having an ether bond in the molecule (i.e. oxygen, which readily

yields oxonium compounds) and for example, with ethyl ether, N 2 O 4 .2(C 2 H 5 ) 2 O

(m. p. -74.8°C), and with dioxane, tetrahydrofuran and tetrahydropyran (Rubin,

Sisler and Shechter [57]).

Battegay and Kern [58] treated methylaniline with nitrogen dioxide and

obtained p- nitro-N-nitrosomethylaniline or, with nitrogen dioxide in excess, 2,4-di-

nitromethylaniline. From dimethylaniline p- nitroso- and p- nitrodimethylaniline

have been obtained, and with an excess of nitrogen dioxide, 2,4-dinitrodimethyl-

aniline. Similar results have been obtained by Schaarschmidt, Balcerkiewicz and

Gante [39].

Extensive studies on the nitration of aromatic compounds with nitrogen dioxide

have been carried out by Shorygin and Topchiyev [59] and later, since 1939, by

Topchiyev [60]. Here are the most important results of their investigations.

(1) Benzene and naphthalene are nitrated with nitrogen dioxide at 18-20°C

to yield mononitro derivatives. At 60°C polynitro compounds are obtained as well.

Ultra-violet irradiation does not affect the nitration yield.

(2) Nitration of aromatic hydrocarbons with a side chain gives mononitro

compounds with the nitro group attached either to the ring or to the side chain,

with a predominance of the former. For example, from toluene at temperature
14-15°C, 46% of nitrotoluenes and 9% of phenylnitromethane were obtained.
The nitration yield seems to increase under the influence of ultra-violet radia-

tion. For example, from m- xylene, 81% of nitro compounds were obtained without

applying irradiation, and 99% when using it.

(3) Phenols are nitrated readily to di- and tri-nitro derivatives.
(4) The nitration of amines results partly in the formation of ring nitrated
compounds and partly in formation of nitro derivatives of phenols. For example

from aniline small quantities of p- nitroaniline were obtained along with 2,4-di-

nitrophenol as the principal product.