Organic Reactions Volume 4 - Sciencemadness Dot Org

SYNTHESIS OF BENZOQUINONES BY OXIDATION 319
scribed 76 as "the most rapid and efficient procedure known at present
for preparation of the polymethylquinones in quantity.'' Several com-
OH OH OH
Rr^NK +N2C6H4SO3- Rf^NR Na2S2O4 Rr^NR TT AT^ TT ^ AT
L > J L * J L + H2NC6H4SO3Na
K^^R NaOH K^^K R^^R (water
soluble)
R=H, CH3, etc.) N=NC6H4SO3Na NH2
o Y
binations of coupling agents and reducing agents have been studied, 38,76
but all are less successful than the process of coupling with diazotized
sulfanilic acid and reducing with sodium hydrosulfite. The coupling
should be carried out in strongly alkaline solution, and adequate
time should be allowed for completion. The preferred oxidizing agent
is ferric chloride, or ferric sulfate where ferric chloride causes chlorination.
33 ' 34 The ferric salt is added to an aqueous solution of the amine or
its salt, and the mixture is steam-distilled at once. If the quinone is
very sensitive (e.g., o-xyloquinone 85 ) steam distillation is carried out
at reduced pressure. Coupling and reduction are commonly carried
out as consecutive reactions without isolation of the intermediate, and
the crude amine is usually oxidized without purification. Overall yields
are rarely less than 60% and occasionally, as in the preparation of
pseudocumoquinone 76 from the phenol, may be as high as 95%. Even
unsaturated quinones, 83 such as allylquinone and allyltrimethylquinone,
are obtained in quite satisfactory yields.*
Although coupling is the most generally successful method for preparing
p-aminophenols, other methods have found some application. One
is the electrolytic reduction of the appropriate nitro compound. 86 ' 87
Nitration of a phenol, followed by reduction of the nitro group, has been
used, and in representative procedures 88 * 89 good results have been obtained
by oxidizing the aminophenoj. with chromic acid-sulfuric acid at
0°. Nitrosation and reduction have also been used successfully, 90 ' 91 ' 9101
* For another method of preparing unsaturated quinones see p. 322.
86 Gattermann, Ber., 27, 1931 (1894).
87 Raiford, Am. Chem. J., 46, 425 (1911).
88 van Erp, Rec. trav. chim., 30, 284 (1911).
89 van Erp, Ber., 58, 663 (1925).
90 Hodgson and Moore, J. Chem. Soc, 1926, 2039.
91 Hodgson and Nicholson, J. Chem. Soc, 1942, 375.
810 Karrer and Schlapfer, HeIv. Chim. Acta, 24, 298 (1941).