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118 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

Cohen and Wibaut [151] in their work, already mentioned (p. 44), on the

nitration of aromatic hydrocarbons with a mixture of nitric acid and acetic an-

hydride, confirmed the catalytic action of nitrous acid in this case too. As the re-

action proceeded the concentration of nitrous acid increased owing to the oxidizing

action of nitric acid on the hydrocarbon.

Titov [34] proved, after having investigated a large group of aromatic compounds,

including phenols, naphthalene, etc. that pure nitric acid (d 1.40) free from nitrous

acid had no nitrating properties at all. The true nitrating agent, the author believed,

was NO 2 , as mentioned before. Titov’s scheme is as follows:

(67)

lngold and his co-workers [152] when investigating the nitration of phenols

and their ethers, came to the conclusion that it was the nitrosonium ion, NO

+

,

formed as a result of the hypothetical reactions (a) and (b):

HNO 2 + HNO 3 <-> H 2 NO 2 + + NO 3 - (a)

H 2 NO 2 + <-> NO+ + H 2 O (b)

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

that had initiated nitration reactions, eqn. (c) deriving from eqns (a), and (b).

The nitrosonium ion may react according to the equation:

ArH + NO+ -> ArHNO+ -> ArNO + H+ (68)

the nitroso compound formed being rapidly oxidized to a nitro compound:

ArNO + HNO 3 -> Ar-NO 2 + HNO 2 (69)

Schramm and Westheimer [153] have observed that when a phenyl ether such

as anisole is nitrated, the presence of nitrous acid is also necessary. The authors

believed nitrosoanisole was formed as an intermediate product as in the nitration

of phenol. Their assumption was based on the fact that p- nitrosoanisole yields

nitration products identical to those given by anisole, viz. nitroanisoles and 2,4-di-

nitrophenol. Thus, beside the nitration, a partial break-down of the ether bond

takes place.

A partial dearylation of diarylether during nitration had already been observed

by Reilly, Drumm and Barrett [154]. The dealkylation, observed by Schramm

and Westheimer, has been confirmed by Ingold and his co-workers [152]. For

example p- chloroanisole, when nitrated with a 6N solution of nitric acid in the
presence of acetic acid at 20°C gave 4-chloro-2-anisole in 66% yield and 4-chloro-

2,6-dinitrophenol in 33% yield of theory.
Simultaneously the methyl group, after being split off from p- chloroanisole,