A solution of
105.1 g. (0.5 mole) of benzil (Note 1) in 325 ml. of n-propyl alcohol is prepared in a
1-l. round-bottomed flask which is fitted with an
efficient reflux condenser. To this solution
76 g. (1.30 moles) of 85% hydrazine hydrate (Note
2) is added, and the mixture (Note
2) is heated under reflux for 60 hours. The solution is cooled with an
ice bath, and the
benzil dihydrazone is separated by suction filtration. The crystals are washed with
200 ml. of cold, absolute ethanol and dried (Note
3) on the
suction filter for 1 hour. The yield of
benzil dihydrazone is
99–106 g. (
83–89%), m.p.
150–151.5°.
The
benzil dihydrazone is added to
480 ml. of reagent grade benzene in a
1-l. three-necked flask fitted with a reflux condenser and a
sealed stirrer. A small amount of yellow
mercuric oxide (2–4 g.) is added to the mixture with stirring to keep the
benzil dihydrazone suspended, and the mixture is warmed slightly on a
steam bath.
Nitrogen is evolved, and the mixture turns gray. Additional yellow
mercuric oxide is then introduced in small portions so as to keep the reaction mixture gently refluxing until a total of 240 g. (1.11 moles) has been added. The mixture is stirred for 1 hour and allowed to stand overnight. It is then filtered, and the residue (
mercury and
mercuric oxide) is washed with
100 ml. of benzene, which is combined with the original red
benzene is filtrate. After drying over anhydrous
sodium sulfate, the
benzene is removed by distillation under reduced pressure by heating with a
water bath. The residue is distilled from a flask connected to a short distillation head at
95–105°/0.2–0.3 mm. and yields
60–65 g. (
67–73% from
benzil) of
diphenylacetylene, m.p.
59–60°. The product can be recrystallized from
100 ml. of 95% ethanol, m.p.
60–61° (Note
4).