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NITRATION AGENTS AND METHODS MORE RARELY USED 119

formed methyl acetate. Cook and Bunnett [155] have tried to explain the pheno-

menon of splitting off the methyl group as the result of the formation of a tran-

sient oxonium ion, which, as is known, is able to give off an alkyl radical:

On the other hand Ingold and co-workers [144,155a] have proved that the

presence of nitrous acid in the nitrating acid decreases the rate of nitration of

aromatic compounds in general with the exception of phenols. The same holds

true for phenyl ethers (e.g. anisole) which are more difficult to nitrate with higher

concentrations of nitric acid in acetic acid (e.g. 8N) in the presence of nitrous

acid, whereas with a less concentrated nitric acid (e.g. 5N), nitrous acid accele-

rates the reaction.

Nitrous acid itself can act as a nitrating agent. This was noticed for the first

time by Niementowski [156] and Koch [157].

Niementowski reacted sodium nitrite with a solution of 3,4-bis(dimethylamine)-

toluene in acetic acid and obtained a nitro derivative:

(70)

m. p. 63°C

Similarly Koch prepared chloronitrodimethylaniline by acting with a stoichio-

metric quantity of sodium nitrite on an acid solution of p- chlorodimethylaniline.

Pinnov and Schuster [158] confirmed his results.

A number of other authors have also nitrated aromatic amines, acting with

sodium nitrite on the amine dissolved in hydrochloric or acetic acid. Thus, tri-

phenylamine and its methyl derivative in acetic acid were nitrated by Häussermann

and Bauer [159], and Rupe, Braun and Zembruski [160] and Tsuruta and Oda

[161] nitrated derivatives of dimethylaniline in hydrochloric acid to yield mononitro

products.

Deninger [162] discovered that salicylic acid can be nitrated with nitrous acid

to yield mononitrosalicylic acids :