Organic Reactions Volume 4 - Sciencemadness Dot Org

326 ORGANIC REACTIONS
few degrees low (m.p. 29-30° i02 ), the quinone does not need to be purified
further for most purposes. Distillation is a satisfactory method of
purification; b.p. 98°/10 mm., 108°/18 mm.
2,5-Diphenylquinone. 110 To a suspension of 300 g. of finely powdered
anhydrous aluminum chloride in 500 ml. of dry benzene in a 2-1., threenecked
flask, equipped with a mechanical stirrer, 500-ml. separatory
funnel, thermometer, and reflux condenser, is slowly added with stirring
a solution of 100 g. of pure benzoquinone.in 1 L of dry benzene. The
rate of addition is regulated (two to three hours required) to maintain
the reaction mixture at a temperature of 35-40°. Stirring is continued
for five hours, during which time the temperature is allowed to drop to
that of the room. The reaction mixture is decomposed by pouring it
slowly into a mechanically stirred mixture of 2 kg. of ice and 250 ml. of
concentrated hydrochloric acid. Stirring is continued until a lightbrown
emulsion is formed and no lumps of undecomposed material
remain. After the benzene has been removed by steam distillation, the
residual light-brown granular solid is collected and washed with hot
water and dried. The dry material (140 g.) is green and is a mixture of
quinones, hydroquinones, and quinhydrones. The crude product is
placed in a 54., round-bottomed flask with 3 L of glacial acetic acid and
21.5 g.* of chromic anhydride, and the mixture is rapidly heated to
boiling. The solution is immediately filtered through a large fluted
filter and the filtrate cooled for two to three hours in running water*
The yellow flakes of diphenylquinone are collected and washed first with
water and then with 150 ml. of 50% ethanol. The dried material weighs
51 g. and melts at 210-212°. It is pure enough for most purposes, but a
single recrystallization from benzene or glacial acetic acid yields the
pure substance melting at 214°. An additional 7 g. of pure material
may be obtained from the mother liquors; thus the total yield is 58 g.
(72%; this figure is based on the fact that three moles of quinone are
required to give one mole of diphenylquinone, if no oxidizing agent other
than quinone is present).
3,5-Dibromotoluquinone. 26 A solution of 10 g. of tribromo-m-cresol 22
(m.p. 82-83°) in 500 ml. of 70% acetic acid is heated to 70°, 3.2 g. of
chromic anhydride is added, and the temperature is maintained at 70-
75° for ten minutes. After the addition of 1.5 1. of water the yellow solid
is collected and recrystallized from dilute ethanol. There is obtained
6.2 g. (77%) of quinone melting at 114-115°.
* The amount of chromic anhydride required may be determined by boiling 1-g,
samples in 25 ml. of glacial acetic acid with various amounts of chromic anhydride lot
two to three minutes, filtering, and cooling. The proper amount of oxidizing agent gives
yellow quinone not contaminated with green quinhydrone. Excess oxidizing agent destroys
the desired quinone.