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Org. Synth. 1932, 12, 34
DOI: 10.15227/orgsyn.012.0034
4,5-DIPHENYLGLYOXALONE
[2(5)-Imidazolone, 4,5-diphenyl-]
Submitted by B. B. Corson and Emeline Freeborn.
Checked by Frank C. Whitmore and Marion M. Whitmore.
1. Procedure
A mixture of 212 g. (1 mole) of benzoin (Note 1), 110 g. (1.8 moles) of urea and 800 cc. of glacial acetic acid in a 2-l. round-bottomed flask is heated under a reflux condenser for seven hours (Note 2). The hot solution is quickly poured into a 2-l. beaker (Note 3) and allowed to stand at least three hours. The cold mixture is then transferred by means of a large wooden spoon or spatula to a 30-cm. Büchner funnel and sucked as dry as possible with the help of a rubber dam. The crystals are pressed down during the suction filtration. The filtrate is discarded. The crystals are returned to the beaker, stirred mechanically with 500 cc. of ether for thirty minutes, filtered again by suction (Note 4), and spread out to dry at least overnight (Note 5). The product is dissolved by heating with 1 l. of glacial acetic acid in a 2-l. round-bottomed flask attached to a reflux condenser (Note 6), and the clear solution is poured, with mechanical stirring, into 2.5 l. of water in a 4-l. (1-gal.) crock. Stirring is continued for thirty minutes (Note 7). The mixture is filtered on a 30-cm. Büchner funnel and pressed and sucked as dry as possible. The crystals are transferred to the 2-l. beaker and stirred mechanically for ten minutes with 1 l. of water. After filtration, the washing with water is repeated. The product is then returned to the beaker, stirred with 750 cc. of ether, and filtered again. The material is then air-dried to constant weight. The yield of white fluffy crystals of diphenylglyoxalone melting at 330–335° (corr.) (Note 8) is 220–230 g. (93–97 per cent of the theoretical amount).
2. Notes
1. The benzoin (Org. Syn. Coll. Vol. I, 1941, 94) need not be recrystallized.
2. At first the color is reddish orange but later it changes to dark yellow.
3. If left in the flask the product solidifies too much to be removed readily.
4. Unreacted benzoin is removed by the ether, in which diphenylglyoxalone is only sparingly soluble.
5. The product is difficult to dry completely.
6. This step is not successful if less than 1 l. of glacial acetic acid is used.
7. The water removes unreacted urea.
8. The melting point is conveniently taken on the surface of mercury heated in a test tube with the thermometer dipping in the mercury.
3. Discussion
The only method of preparative interest is the interaction between benzoin and urea in acetic acid solution as described by Biltz1 and Chattaway.2

References and Notes
  1. Biltz, Ann. 368, 173 (1909).
  2. Chattaway and Coulson, J. Chem. Soc. 1928, 1363.

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

4,5-Diphenylglyoxalone

2(5)-Imidazolone, 4,5-diphenyl-

diphenylglyoxalone

acetic acid (64-19-7)

ether (60-29-7)

mercury (7439-97-6)

Benzoin (119-53-9)

urea (57-13-6)