Org. Synth. 1947, 27, 30
DOI: 10.15227/orgsyn.027.0030
[Indone, 2,3-diphenyl-]
Submitted by C. F. H. Allen, J. W. Gates, Jr., and J. A. VanAllan.
Checked by R. L. Shriner and H. W. Johnston.
1. Procedure
A solution of phenylmagnesium bromide is prepared in the usual manner1 using 12.2 g. (0.5 gram atom) of magnesium, 78.5 g. (52 ml., 0.5 mole) of bromobenzene, and 500 ml. of absolute ether in a 2-l. round-bottomed three-necked flask fitted with a reflux condenser, a mechanical stirrer, and a dropping funnel. No unreacted magnesium should remain; if any does, an additional 1–2 ml. of bromobenzene should be added.
To this vigorously stirred solution is added slowly a solution of 44.5 g. (0.20 mole) of benzalphthalide2 in 400 ml. of dry benzene. After about half of this solution has been added, the magnesium complex begins to separate; it hinders the stirring somewhat. When all the phthalide solution has been admitted (about 1 hour), the reflux condenser is replaced by a still head carrying a thermometer and attached to a condenser set for downward distillation. The bulk of the solvent is then removed; this requires about 30 minutes, the temperature of the vapor remaining at 50° for about half this time and rising to about 65° toward the end. About 220–230 ml. of distillate is obtained. The flask and contents are then immersed in an ice bath, and the magnesium complex is decomposed by the slow addition of a cold solution of 15 ml. of concentrated sulfuric acid in 300 ml. of water (Note 1) with rapid stirring. The upper benzene layer is separated and transferred to a 1-l. Claisen flask, and the solvent is removed by distillation from a steam bath; this requires about 4 hours. The residual thick red syrup is transferred to a 125-ml. Claisen flask with a wide side arm set up for vacuum distillation. The residue is heated under a pressure of about 10 mm. to remove all low-boiling material (Note 2) and then is distilled under reduced pressure. The fraction boiling at 215–255°/6 mm. (195–220°/1 mm.) is collected, most of the distillate coming over at 235–240°/6 mm. The distillate is dissolved in 50 ml. of boiling benzene, 200 ml. of hot 95% ethanol is added, and the solution is chilled in an ice bath for 2 hours. The red, crystalline 2,3-diphenylindone is collected on a filter, washed with 50 ml. of cold 95% ethanol, and air-dried. The yield is 34–40 g. (60–71%) of red crystals melting at 149–151° (Note 3) and (Note 4).
2. Notes
1. The decomposition is vigorous, and the acid must be admitted slowly at first but may be added more rapidly toward the end.
2. During this heating any carbinol present is dehydrated. Low and erratic yields usually indicate incomplete dehydration.
3. The product may be recrystallized by dissolving it in 50 ml. of boiling benzene and diluting with 200 ml. of hot ethanol. The recovery of material, m.p. 150–151°, is about 90%.
4. This procedure is capable of considerable variation, by which other indenones may be secured. For example, the benzalphthalide may be replaced by other phthalides made from (a) other aldehydes, or (b) other anhydrides; the phenylmagnesium bromide can be replaced by other Grignard reagents.
3. Discussion
2,3-Diphenylindone has been prepared by the action of phenylmagnesium bromide upon benzalphthalide3,4 and by ring closure from α,β-diphenylcinnamic acid5,6 or from 2,3,3-triphenyl-3-hydroxypropionic acid.7,8

References and Notes
  1. Org. Syntheses Coll. Vol. 1, 226 (1941).
  2. Org. Syntheses Coll. Vol. 2, 61 (1943).
  3. Löwenbein and Ulich, Ber., 58, 2662 (1925).
  4. Weiss and Sauermann, Ber., 58, 2736 (1925).
  5. Meyer and Weil, Ber., 30, 1281 (1897).
  6. Weitz and Scheffer, Ber., 54, 2341 (1921).
  7. Ivanoff and Ivanoff, Compt. rend., 226, 1199 (1948).
  8. Ivanoff and Ivanoff, Annuaire univ. Sofia, Faculté sci., 44, (2), 121 (1947–1948) [C. A., 44, 3960 (1950)].

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

Indone, 2,3-diphenyl-

magnesium complex


ethanol (64-17-5)

sulfuric acid (7664-93-9)

Benzene (71-43-2)

ether (60-29-7)

magnesium (7439-95-4)

bromobenzene (108-86-1)

Phenylmagnesium bromide (100-58-3)

Benzalphthalide (575-61-1)

2,3-DIPHENYL-1-INDENONE (1801-42-9)

α,β-diphenylcinnamic acid

2,3,3-triphenyl-3-hydroxypropionic acid