A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1954, 34, 42
DOI: 10.15227/orgsyn.034.0042
[Acetylene, diphenyl-]
Submitted by Arthur C. Cope, Douglas S. Smith, and Robert J. Cotter1.
Checked by Charles C. Price and Thomas F. McKeon, Jr..
1. Procedure
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).
2. Notes
1. Eastman Kodak Company white label grade benzil or material prepared by the procedure described in Organic Syntheses2 is satisfactory.
2. Hydrazine hydrate (85%) as supplied by the Edwal Laboratories was used. On addition of this reagent to the benzil solution, the monohydrazone of benzil precipitates, but it redissolves readily on heating.
3. Benzil dihydrazone should not be dried in a vacuum desiccator, for it sublimes easily.
4. Diphenylacetylene prepared by this method has the advantage of being uncontaminated with stilbene, with which it forms a solid solution not readily separable.3 Di-p-tolylacetylene4 and α-naphthylphenlacetylene5 have been prepared by the same method in high yields.
3. Discussion
In addition to the methods mentioned in a previous preparation,6 diphenylacetylene has been prepared by the action of potassium hydroxide on 5,5-diphenyl-3-nitroso-2-oxazolidone (100%),7 on meso-stilbene dibromide in triethylene glycol,8 and on stilbene tetrabromide in butyl alcohol;9 by the condensation of bromobenzene with sodium phenylacetylide in liquid ammonia,10 by the oxidation of benzil dihydrazone with silver trifluorocetate in triethylamine,11 and by the pyrolysis of α-benzoylbenzylidenetriphenylphosphorane.12 The present procedure is a modification of that of Schlenk and Bergmann.13
This preparation is referenced from:

References and Notes
  1. Massachusetts Institute of Technology, Cambridge, Massachusetts.
  2. Org. Syntheses Coll. Vol. 1, 87 (1941).
  3. Pascal and Normand, Bull. soc. chim. France, [4] 13, 151 (1913).
  4. Kastner and Curtius, J. prakt. Chem., [2] 83, 225 (1911).
  5. Ruggli and Reinert, Helv. Chim. Acta, 9, 67 (1926).
  6. Org. Syntheses Coll. Vol. 3, 350 (1955).
  7. Newman and Kutner, J. Am. Chem. Soc., 73, 4199 (1951).
  8. Fieser, J. Chem. Educ., 31, 291 (1954).
  9. Drefahl and Plötner, Chem. Ber., 91, 1280 (1958).
  10. Scardiglia and Roberts, Tetrahedron, 3, 197 (1958).
  11. Newman and Reid, J. Org. Chem., 23, 665 (1958).
  12. Trippett and Walker, J. Chem. Soc., 1959, 3874.
  13. Schlenk and Bergmann, Ann., 463, 76 (1928).

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

monohydrazone of benzil


ethanol (64-17-5)

ammonia (7664-41-7)

Benzene (71-43-2)

sodium sulfate (7757-82-6)

nitrogen (7727-37-9)

mercury (7439-97-6)

mercuric oxide (21908-53-2)

butyl alcohol (71-36-3)

Benzil (134-81-6)

potassium hydroxide (1310-58-3)

bromobenzene (108-86-1)

n-propyl alcohol (71-23-8)

hydrazine hydrate (7803-57-8)

sodium phenylacetylide


Acetylene, diphenyl- (501-65-5)

triethylamine (121-44-8)

Benzil dihydrazone (4702-78-7)


triethylene glycol (112-27-6)

stilbene tetrabromide

silver trifluorocetate



meso-stilbene dibromide