with quinine in cinchona bark), is now prepared from aniline.
The aniline, in process of oxidation to quinone, appears to pass
through the following intermediate stages,
The aniline is first oxidised to phenylammonium oxide, which
changes into phenylhydroxylamine. The latter also under-
goes intramolecular change, being converted into /-amino-
phenol, which is finally oxidised to quinone (Bambcrger).
It may also be obtained "by the,oxidation of para-derivatives of
aniline, such as /-phenylenediamine, sulphariilic acid, p.
aminophenol, &c. Other amino-compounds and phenols yield
corresponding quinones, and it can even be prepared from an
amino-compound or phenol, if an alkyl group occupies the para-
position, as in the case of mesidine, which loses a methyl group
and yields jw-xyloquinone. Quinone is sometimes regarded as a
superoxide (Graebe), sometimes as a para-diketonc (Kittig).
The facts in favour of the first are that quinone, like a peroxide,
has a strong oxidising action, that on reduction it yields, not a
glycol, but a dihydroxybenzene ; moreover, with PCI.-, instead
of a tetra-chloro-derivative, a dichloroben/.cnc is formed. In
favour of the ketone structure is the formation of a mono- and