The hot reaction mixture is poured with stirring over about 0.75 l. of crushed ice in a
2-l. beaker. The beaker is filled with water, and the mixture is stirred to dissolve inorganic salts (Note
5). The insoluble red-brown solid is collected on a
suction filter. This crude product, even while damp, is transferred to a
2-l. round-bottomed flask, and
500 ml. of a mixture of 75% (375 ml.) of petroleum ether (b.p.
90–100°) and
25% (125 ml.) of benzene is added. The flask is provided with a
reflux condenser, and the mixture is heated at reflux for 15 minutes by means of an electric mantle (Note
6). The resulting solution is decanted into a second 2-l. flask, leaving in the first flask some water and a red-brown solid residue. To the slightly cooled liquor in the second flask is added cautiously
7 g. of powdered activated carbon. The
carbon is dispersed by swirling, and the mixture is heated for an additional 5 minutes. The mixture is then filtered through a
fluted filter into a
1-l. Erlenmeyer flask. This flask is stoppered and chilled to cause crystallization of the product (Note
7).
The product is collected on a suction filter. The yield of air-dried product, as yellow-orange crystals, m.p.
87–89°, is
38–42 g. (
65–71%) (Note
8). A purer, lemon-yellow product, m.p.
88.5–90°, is obtained by an additional recrystallization from
1 l. of petroleum ether (b.p.
90–100°) with use of
carbon; the yield after this second crystallization is
28–34 g. (
48–58%).