Organic Reactions Volume 4 - Sciencemadness Dot Org

322 ORGANIC REACTIONS
the initial condensation rarely gives a pure hydroquinone, for this is
oxidized in part by quinone, and there results a mixture of diarylquinone,
diarylhydroquinone, and the quinhydrone (molecular complex of the
quinone and the hydroquinone). The diarylquinone is obtained by
completing the oxidation of this mixture (for detailed procedure see
p. 326). Since these compounds are rather insoluble in water, the oxidation
is preferably carried out in organic media, e.g., ferric chloride in
acetic acid, 112,114 quinone in boiling ethanol, 107 ' 111 or chromic anhydride in
acetic acid. 110
Higher alkylhydroquinones can be prepared 116 by Clemmensen reduction
and demethylation of the corresponding acylhydroquinone dimethyl
ethers. 2,3- and 2,5-Diallylhydroquinone result from rearrangement of
the diallyl ether of hydroquinone. 117 The diallylquinones are prepared
in good yield by oxidation with silver oxide.*
Many haloquinones have been synthesized by oxidation of the corresponding
halogen-substituted hydroquinones, prepared by addition of
halogen acid to the appropriate quinone. 25 ' 59,118 If an alkyl group or
halogen is present in the quinone the halogen acid adds in such a way
that the two substituents bear the 2,5-relationship. 119-121 When both
alkyl and halogen are present in a quinone the position at which a second
halogen enters has not been established. The addition of hydrogen
chloride to 5-bromotoluquinone and oxidation of the product 122 affords
a compound which melts at 150° and which is probably 5-bromo-6chlorotoluquinone,
for the only other possibility (except by rearrangement)
is 5-bromo-3-chlorotoluquinone, m.p. 119 0 . 123 Hydrogen chloride
adds to 5-chlorotoluquinone, 124 and the product can be oxidized to a
quinone which melts at 85-86° and which is probably 5,6-dichloro-
* For another method of preparing unsaturated quinones see p. 319.
116 Asano and Hase, /. Pharm. Soc. Japan, 60, 650 (1940).
117 Fiesor, Campbell, and Fry, /. Am. Chem. Soc, 61, 2216 (1939).
118 Schniter, Ber., 20, 1316 (1887).
119 Sarauw, Ann., 209, 106 (1881).
120 Levy and Schultz, Ann., 210, 138 (1881).
121 Hantzsch and Schniter, Ber., 20, 2279 (1887).
122 Schniter, Ber., 20, 2283 (1887).
123 Raiford, J. Am. Chem. Soc, 36, 670 (1914).
124 Kehrmann, Silva, and Keleti, Ber,, 48, 2027 (1915).