A. α,α'-Dibromodibenzyl ketone. To a solution of 70 g. (0.33 mole) of commercial dibenzyl ketone in 250 ml. of glacial acetic acid in a 2-l. one-necked flask fitted with a magnetic stirrer a solution of 110 g. (0.67 mole) of bromine in 500 ml. of acetic acid is added through a dropping funnel over a 15-minute period. After addition is complete, the mixture is stirred for an additional 5 minutes and is then poured into 1 l. of water. Solid sodium sulfite is added in small portions until the initial yellow color of the solution is discharged, and the mixture is allowed to stand for 1 hour. The slightly yellow dibromoketone is then collected by filtration and air-dried. Recrystallization from 1 l. of ligroin yields 97 g. of white needles, m.p. 79–87°; an additional 11 g., m.p. 79–83°, is obtained by concentrating the mother liquors, and the two crops are combined (Note 1).

B. Diphenylcyclopropenone. A solution of 100 ml. of triethylamine (Note 2) in 250 ml. of methylene chloride is magnetically stirred in a 2-l. one-necked flask while 108 g. (0.29 mole) of the above dibromoketone in 500 ml. of methylene chloride is added dropwise over 1 hour. The mixture is stirred for an additional 30 minutes and then extracted with two 150-ml. portions of 3N hydrochloric acid; the aqueous extracts are discarded. The red organic solution is transferred to a 2-l. Erlenmeyer flask and cooled in an ice bath. While this solution is swirled, a cold solution of 50 ml. of concentrated sulfuric acid in 25 ml. of water is slowly added. A slightly pink precipitate of diphenylcyclopropenone bisulfate gradually separates (Note 3). This is collected on a sintered-glass funnel and washed with two 100-ml. portions of methylene chloride. The solid is then returned to the flask (Note 4) along with 250 ml. of methylene chloride and 500 ml. of water, and 5 g. of solid sodium carbonate is added in small portions. The organic layers is collected and the aqueous solution extracted with two 150-ml. portions of methylene chloride. The combined organic layers are dried over magnesium sulfate and evaporated to dryness. The impure diphenylcyclopropenone is recrystallized by repeated extraction with boiling cyclohexane (total 1.5 l.), the solution being decanted in each case from a reddish oily impurity. On cooling, the solution deposits 29 g. of white crystals, and an additional 1 g. can be obtained by concentrating the mother liquors to 150 ml. The combined 30 g., m.p. 119–120°, represents an overall yield of 44% based on dibenzylketone.