In a
3-l. three-necked flask equipped with a
reflux condenser, a
sealed mechanical stirrer, and a
1-l. dropping funnel, are placed
100 g. (0.56 mole) of phenanthrene (Note
1),
210 g. (2.1 moles) of chromic acid (Note
2), and 1 l. of water. The stirrer is started, and
450 ml. of concentrated sulfuric acid is added from the dropping funnel into the suspension at such a rate that gentle boiling is induced (Note
3). After addition of the
sulfuric acid is complete, a mixture of
210 g. (2.1 moles) of chromic acid and 500 ml. of water is added carefully to the reaction mixture from the dropping funnel (Note
4). The resulting mixture is boiled under reflux for 20 minutes.
After being cooled to room temperature the reaction mixture is poured into an equal volume of water and chilled to 10° in an
ice bath. The crude precipitate is separated by suction filtration and thoroughly washed with cold water until the washings no longer show any chrome green color. The precipitate is triturated with three 300-ml. portions of boiling water and filtered to remove the
diphenic acid formed in the reaction. The precipitate is then triturated with several (4–6)
300-ml. portions of hot 40% sodium bisulfite solution and again filtered (Note
5). The insoluble material is a mixture of
anthraquinone and some resinous products derived from
anthracene and other contaminants present in the starting material (Note
6). The
sodium bisulfite filtrates are combined and cooled to 5° in an ice bath. The precipitate which separates is collected by suction filtration; then it is transferred to a
1-l. beaker and finely dispersed in 300 ml. of water. To this suspension is added, with good stirring,
500 ml. of a saturated solution of sodium carbonate. The deep orange
phenanthrenequinone which is liberated is separated by suction filtration (Note
7), washed well with cold water, and dried on a porcelain plate. The yield of product, melting at
205–208° cor., is
52–56 g. (
44–48%). Further purification may be accomplished by crystallization from
95% ethanol (100 ml./ g.). The recovery of first-crop material is over
80%, m.p.
208.5–210° cor.