Organic Syntheses, Coll. Vol. 5, p.514 (1973); Vol. 47, p.62 (1967).
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)
. 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
Care should be taken to prevent either the dibromoketone
or the cyclopropenone
from coming into contact with the skin, as allergic reactions have been observed in several cases. The use of gloves is recommended especially for the bromoketone
. The latter product has a wide melting range because it is a mixture of the meso
- and d,l
If the white solid fails to separate after 15–30 minutes, concentrated sulfuric acid
is added in 4-ml. portions to the cooled solution with swirling until the white solid appears.
Since some of the white solid adheres to the walls of the flask, it is convenient to use the same flask for the neutralization after rinsing it with methylene chloride
4. Merits of the Preparation
is the first stable molecule prepared which has a carbonyl group in a three-membered ring. In a very real sense the compound has aromatic character and is fairly stable.4
An interesting cycloaddition reaction of enamines with diphenylcyclopropenone
has been reported.7
This preparation is referenced from:
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