Organic Syntheses, Coll. Vol. 4, p.698 (1963); Vol. 33, p.50 (1953).
In a 2-l. three-necked flask
, fitted with a mechanical stirrer
, a 1-l. dropping funnel
, and a thermometer
, is placed a solution of 120 g. (1.2 moles) of pure chromium trioxide (Note 1)
in 150 ml. of 80% aqueous acetic acid
. The flask is surrounded by a freezing mixture of ice and salt, and, when the temperature of the contents of the flask has fallen to 0°, a solution of 64 g. (0.5 mole) of naphthalene
in 600 ml. of glacial acetic acid
is gradually added, with constant stirring, over a period of 2–3 hours. The internal temperature is maintained at about 10–15°. Stirring is continued overnight, during which time the reaction mixture and cooling bath
gradually attain room temperature (Note 2)
. The dark green solution is then set aside for 3 days and occasionally stirred.
The crude naphthoquinone
is precipitated by pouring the reaction mixture into 6 l. of water. The yellow precipitate is filtered, washed with 200 ml. of water, and dried in a desiccator
. The product can be crystallized from 500 ml. of petroleum ether
) (Note 3)
and separates in the form of long yellow needles, m.p. 124–125°.
The yield is 14–17 g.
) (Note 4)
An equivalent quantity of technical grade chromium trioxide
, ground to a fine powder, may be employed.
It is necessary to continue vigorous stirring at this stage in order to prevent local overheating and to keep the mixture from setting to a solid mass.
Crystallization from petroleum ether
) is far more convenient than steam distillation as a method of purification, and a product of high purity is obtained after a single crystallization. The checkers used Skellysolve C
) with consistent results. Crystallization from ether
has also been employed.2
The yield is substantially unchanged on increasing the proportion of chromium trioxide
used in the oxidation. The submitters report consistent yields of 25–28 g.
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