B.
Tropolone. A
1-l., three-necked, round-bottomed flask equipped with a
mechanical stirrer, addition funnel, and a
reflux condenser is charged with
500 ml. of glacial acetic acid and then,
cautiously,
100 g. of sodium hydroxide pellets. After the pellets have dissolved,
100 g. (0.565 mole) of 7,7-dichlorobicyclo[3.2.0]hept-2-en-6-one is added and the solution is maintained at reflux under
nitrogen for 8 hours. Concentrated
hydrochloric acid is added until the mixture is about pH 1; approximately 125 ml. of acid is required. After the addition of
1 l. of benzene, the mixture is filtered and the solid
sodium chloride is washed with three
100-ml. portions of benzene. The two phases of the filtrate are separated, and the aqueous phase is transferred to a magnetically stirred, 1-l., continuous extractor (Note
8). The combined
benzene phase is transferred to a
2-l. pot connected to the extractor, and the aqueous phase is extracted for 13 hours. Following distillation of the
benzene, the remaining orange liquid is distilled under reduced pressure through a
30-cm. Vigreux column, removing
acetic acid. When
tropolone begins to distill into the column, the condenser is replaced with a two-necked flask immersed in ice water. With vacuum applied through one neck of this
receiver,
tropolone distills at 60° (0.1 mm.) and is collected as a crude yellow solid,
66.4 g. (
96%). A solution of the impure product in
150 ml. of dichloromethane is diluted with
600 ml. of pentane,
4 g. of activated carbon is added, and the mixture is heated to boiling. After removal of the
carbon by filtration, the solution is maintained at −20° until crystallization is complete.
Tropolone,
53 g. (
77%) (Note
9), is collected as white needles, m.p.
50–51°, by filtration. Evaporation of the filtrate to dryness, dissolution of the residue in
800 ml. of pentane, treatment with activated
carbon, and cooling to −20° yields an additional
8 g. (
12%) of
tropolone as pale-yellow crystals, m.p.
49.5–51°.