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Org. Synth. 1933, 13, 38
DOI: 10.15227/orgsyn.013.0038
DIPHENYL TRIKETONE
[Propanetrione, diphenyl-]
Submitted by Lucius A. Bigelow and Roy S. Hanslick.
Checked by W. W. Hartman and Lloyd A. Smith.
1. Procedure
(A) Dibenzoyldibromomethane.—In a 1-l. three-necked flask, equipped with a mechanical stirrer, a dropping funnel, and a thermometer, are placed 56 g. (0.25 mole) of dibenzoylmethane (Org. Syn. Coll. Vol. I, 1941, 205; Org. Syn. 20, 32) and 14 cc. of chloroform. The flask is surrounded by an ice bath, the stirrer is started, and a solution of 28.5 cc. (88 g., 0.55 mole) of dry bromine (Note 1) in 230 cc. of chloroform is added slowly from the dropping funnel during a period of about thirty minutes. The temperature of the mixture should not exceed 15° during the bromination; the hydrogen bromide evolved is continuously removed by aspirating a gentle stream of air over the surface of the solution. After all the bromine has been added, stirring is continued for about fifteen minutes. The solution is then transferred to a distilling flask, and the solvent is completely removed under diminished pressure at room temperature (Note 2). The slightly colored residue is crystallized from 125 cc. of hot 95 per cent ethyl alcohol. The dibenzoyldibromomethane is obtained in the form of white crystals melting at 94–95°. The yield is 72.4 g. (76 per cent of the theoretical amount) (Note 3).
(B) Diphenyl Triketone Hydrate.—A solution of 34.3 g. (0.42 mole) of fused sodium acetate in 142 cc. of hot glacial acetic acid is prepared in a 1-l. round-bottomed flask; 72.4 g. (0.19 mole) of dibenzoyldibromomethane is added, and the mixture is refluxed until the precipitation of sodium bromide ceases (one and one-half to two hours). The mixture is then cooled to room temperature and diluted with 150–200 cc. of water with constant shaking to dissolve the inorganic salt and to precipitate the triketone hydrate, which separates as a white, curdy mass (Note 4). This is separated by filtration, washed well with water, and dried in an oven at 60°. The melting point varies from 65 to 90°, depending upon the extent of dehydration that occurs during the drying operation. The yield is 41.5 g. (86 per cent of the theoretical amount based on the dibenzoyldibromomethane).
(C) Diphenyl Triketone.—The 41.5 g. (0.16 mole) of triketone hydrate is distilled in vacuum from a Claisen flask heated by means of a sand bath. A distilling flask is used as a receiver, and no condenser is necessary. The neck of the receiving flask must be warmed, however, to prevent clogging of the apparatus by crystallization of the distillate. The anhydrous triketone distils at 174–176°/2 mm. as a reddish oil that solidifies to a light yellow, crystalline mass. This is dissolved in 70 cc. of hot ligroin (b.p. 90–120°); it separates on cooling in light yellow needles which melt at 68–70°. The yield is 35 g. (91 per cent of the theoretical amount based on the triketone hydrate; 59 per cent based on the dibenzoylmethane) (Note 5).
2. Notes
1. The bromine should be dried by washing it with concentrated sulfuric acid.
2. If the solvent is removed by heat at ordinary pressure, there is a decrease both in the yield and the purity of the product.
3. If the recrystallization is omitted, a lower yield of the triketone hydrate is obtained.
4. If the hydrate separates in part in an oily condition, it may be dissolved in a small amount of glacial acetic acid and reprecipitated with an equal volume of water.
5. The triketone is hygroscopic and must be kept in a vacuum desiccator or sealed tube.
3. Discussion
The two general methods for the preparation of diphenyltriketone involve the treatment of dibenzoylmethane with bromine1 and with oxides of nitrogen.2 De Neufville and v. Pechmann, who originated the first method, recommended1 conversion of the diketone to dibenzoylbromomethane and transformation of this to the acetate and then to dibenzoylbromocarbinol acetate which was split to the triketone. This sequence has been used with success by Kohler and Erickson3 to prepare the triketone in good yields, but the present method, mentioned but not described by De Neufville and v. Pechmann,1 is simpler and more direct.

References and Notes
  1. De Neufville and v. Pechmann, Ber. 23, 3375, 3379 (1890).
  2. Wieland and Bloch, ibid. 37, 1524, 1531 (1904).
  3. Kohler and Erickson, J. Am. Chem. Soc. 53, 2308 (1931).

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

oxides of nitrogen

ligroin

ethyl alcohol (64-17-5)

sulfuric acid (7664-93-9)

acetic acid (64-19-7)

sodium acetate (127-09-3)

chloroform (67-66-3)

hydrogen bromide (10035-10-6)

bromine (7726-95-6)

sodium bromide (7647-15-6)

Dibenzoylmethane (120-46-7)

DIPHENYL TRIKETONE,
Propanetrione, diphenyl-,
Diphenyltriketone (643-75-4)

Dibenzoyldibromomethane (16619-55-9)

Diphenyl Triketone Hydrate

triketone hydrate

dibenzoylbromomethane

dibenzoylbromocarbinol acetate