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(Michael S) #1
NITRATION AGENTS AND METHODS MORE RARELY USED 85

3% nitric acid, while 4% acid converts methyl- and ethyl-acetanilide into
the corresponding dinitro derivatives. In 1958 T. Urbanski [19] found that
8-hydroxyquinoline can be converted to the 5,7-dinitro compound by boiling with
8% nitric acid and more recently he and Kutkiewicz [20] have found that
the same result can be obtained by prolonged boiling with nitric acid of concen-

trations as low as 0.5%. However, the reaction occurred only after a certain induction


period which ended by evolution of nitrous fumes. When NaNO 2 was added to


the nitric acid, the reaction started almost immediately. The nitration of 8-hydroxy-


5-nitrosoquinoline leads readily to formation of the same nitration product


without the induction period.
The introduction of the 5-nitro group can easily be explained by nitrosation
of 8-hydroxyquinoline in position 5 and subsequent oxidation of the nitroso com-


pound. No similar explanation can be given with regard to the mechanism of the


introduction of the second nitro group, in position 7, as no nitrosation of nitro-


phenols is known and the formation of “8-hydroxy-5-nitro-7-nitrosoquinoline”,


does not seem to be possible. The formation of “5,7-dimtroso-8-hydroxyquinoline”


as an intermediate is also improbable because no instance of the introduction of


two nitroso groups into a monophenol is known. Thus nitration most likely pro-


cedes through the formation of the 5-nitroso derivative only.


It has also been found that 5-nitro-8-hydroxyquinoline can be nitrated with
1% nitric acid to yield 5,7-dinitro-8-hydroxyquinoline. This excludes nitrosation
as an intermediate step for the reason given above:

The introduction of the nitro group into position 7 would support the view
already expressed (p. 48) that the NO 2


+
ion is not the only nitrating agent.
Slavinskaya [21] in 1957, found that phenol can be nitrated to o-, p- and 2,4-

dinitrophenol using nitric acid dissolved in ethyl nitrate at a concentration as low


as 0.5% HNO 3. Phenetole and naphthalene can also be nitrated with this solution


to yield mononitro products. The presence of NO 2 was essential for successful
nitration at such a low concentration of HNO 3.

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