An intimate mixture of
35 g. (0.094 mole) of tetraphenylcyclopentadienone (p. 806) and
9.3 g. (0.095 mole) of maleic anhydride is placed in a
200-ml. round-bottomed flask (Note
1), and to it is added
25 ml. of bromobenzene. After the mixture has been refluxed gently for 3.5 hours (Note
2), it is cooled (Note
3), a solution of
7 ml. of bromine in
10 ml. of bromobenzene is added through the condenser, and the flask is shaken until the reagents are thoroughly mixed. After the first exothermic reaction has subsided, the mixture is refluxed gently for 3 hours (Note
4). The flask is then immersed in a
cooling bath and the temperature of the mixture is held at 0–10° for 2–3 hours. The mixture is filtered with suction, and the crystalline product is washed three times with
10-ml. portions of petroleum ether (b.p.
60–68°). After the product has been dried in the air, it weighs
37–38 g. (
87–89%) and melts at
289–290°. It is light brown, but when pulverized it is almost colorless. The filtrate, when diluted with an equal volume of
petroleum ether and cooled to 0–10°, yields an additional
2–3 g. of a less pure product which melts at
285–288°. The impure material may be purified by recrystallization from
benzene, using
8–9 ml. of benzene per gram of solid (Note
5).