A
300-ml., three-necked, round-bottomed flask is fitted with a
sealed mechanical stirrer, a
thermometer, and a
reflux condenser to which is attached a T-tube connected to a source of pure
nitrogen. The remaining joint of the T-tube is connected to a bubbling device so that the rate of
nitrogen flow can be observed throughout the course of the reaction. The flask is flushed with
nitrogen and charged with
30 ml. of anhydrous dimethyl sulfoxide (Note
1) and
2.4 g. of about 50% sodium hydride in oil (ca. 0.05 mole) (Note
2). Stirring is begun and the contents of the flask are heated to 75° for 30 minutes (Note
3) under a slight pressure of
nitrogen. The flask is cooled in a
water bath to 30°, before a solution of
4.45 g. (0.0250 mole) of diphenylacetylene in 20 ml. of anhydrous dimethyl sulfoxide is added dropwise with stirring to the dark-gray solution. During the addition, the temperature of the reaction mixture gradually rises until it approaches 40°. After the addition is completed, the reaction mixture is heated to 65° and held at this temperature for 2.5 hours. The resulting red-brown reaction mixture is cooled to room temperature and poured into 500 ml. of an ice and water mixture with stirring. After the ice has melted, the mixture is extracted with five
150 ml. portions of diethyl ether. The
ether extracts are combined, washed with three 100-ml. portions of water, then dried over
sodium sulfate. The
ether is removed by distillation at reduced pressure, and the product (about 6.0 g.) is chromatographed on
180 g. of alumina (Note
5). Elution with
1:7 (v/v) benzene:n-hexane gives ten 50-ml. fractions, of which the first two contain nearly all the mineral oil from the
sodium hydride reagent. Fractions 3 through 8 are combined, and the
ether is removed by distillation, yielding
1.2–1.4 g. (
22–25%) of slightly impure
2,3-diphenyl-1,3-butadiene (Note
6). Recrystallization from
methanol gives
0.55–0.70 g. (
10.7–13.6%) of pure
2,3-diphenyl-1,3-butadiene, m.p.
47–48° (Note
7).