A solution of
45 g. (0.25 mole) of trans-stilbene in
750 ml. of ether is prepared in a
1-l. three-necked round-bottomed flask fitted with a
reflux condenser, an
efficient mechanical stirrer, and a
dropping funnel. To the well-stirred solution there is added
13.8 ml. (43 g.; 0.27 mole) of bromine, during the course of 10 minutes. A solid begins to separate in 5 minutes, but stirring is continued for 1 hour. The product is collected on a
Büchner funnel and washed with
ether until it is white. The yield of
stilbene dibromide, melting at
235–237°, is
65.8–69.1 g. (
77–81%).
A solution of
90 g. of potassium hydroxide in
150 ml. of absolute ethanol is prepared in a
500-ml. round-bottomed flask fitted with a
reflux condenser (Note
1). The solution is cooled somewhat, and the
stilbene dibromide is added in several portions (Note
2). The mixture is then refluxed for 24 hours in an
oil bath (Note
3). The hot mixture is poured into 750 ml. of cold water, and the product is removed by filtration and washed with 50 ml. of water. The crude
diphenylacetylene is dried over
calcium chloride in a
vacuum desiccator for 18 hours at room temperature. The chunky, pale yellow crystals melt at 58–60° and weight
33.7–37.8 g. By recrystallization of this product from
50 ml. of 95% ethanol there is obtained
29.2–30.5 g. (
66–69% based on the
stilbene) of pure
diphenylacetylene, which forms white needles melting at
60–61° (Note
4).