In a dry 2-l. three-necked flask are placed 600 g. (4 moles) of freshly distilled ethyl benzoate and 60 g. (0.5 mole) of freshly distilled acetophenone (Note 1). The flask is fitted with a mercury-sealed stirrer which must be rugged enough to stir the reaction mixture even after it becomes very viscous (Note 2). A condenser for downward distillation is attached to one of the necks, and a 500-ml. filter flask is used as the receiver. This receiver is connected to a water pump through a suction flask carrying a two-holed rubber stopper, one hole of which is left open. The reaction flask is heated in an oil bath kept at 150–160°, and, after the mixture is hot, 44 g. (0.65 mole) of sodium ethoxide (Note 3) is added through the third arm of the flask in 1- to 2-g. portions. The ethoxide addition can be conveniently accomplished with a spoon shaped to enter the arm of the flask or by placing a very short-stemmed large funnel in the third neck and pushing the ethoxide through the funnel with a small glass rod or wire spatula. The reaction mixture becomes orange immediately; ethanol distils after the first few additions, and thereafter the evolution of ethanol is quite vigorous. The additions are made as rapidly as evolution of the ethanol permits. During the ethoxide addition a gentle stream of air is kept passing through the flask by means of a water pump attached to the receiver in order to prevent the ethanol vapor from rising in the third arm of the flask and interfering with the addition (Note 4).

After all the ethoxide has been added (20–30 minutes) the gelatinous reaction mixture is stirred until no more distillate comes over (15–30 minutes). The weight of this distillate amounts to 38–45 g. (Note 5).

The oil bath is removed, and, with the stirring maintained, the reaction mixture is cooled to room temperature by running cold water over the flask. Then 150 ml. of water is added to dissolve the reaction mass, and both layers of the mixture are transferred to a separatory funnel. An ice-cold solution of 25 ml. of concentrated sulfuric acid in 200 ml. of water is added, and the mixture is shaken vigorously. The ester layer is separated and washed with 200 ml. of water; it is then shaken with successive 200-ml. portions of 5% sodium bicarbonate solution until the evolution of carbon dioxide ceases, after which it is washed with 200 ml. of water. The bicarbonate solution is separated and extracted with 100 ml. of ether (Note 6). The ether extract, after washing with 50 ml. of water, is combined with the ester layer and the resulting ethereal solution dried with 40 g. of calcium chloride. The ether is removed by distillation from a water bath, and the excess ethyl benzoate is removed by distillation under reduced pressure. The recovered ester, b.p. 80–83°/8 mm., amounts to 475–490 g. After the ester is removed the temperature of the oil bath is slowly raised to 180–185° while the system is maintained under 8 mm. pressure. A small amount of liquid distilling higher than the ester is thus removed. When no more distillate comes over at this temperature, the remaining oil, while still warm, is poured into a 500-ml. Erlenmeyer flask and allowed to crystallize. This crude dibenzoylmethane weighs 92–108 g. and is usually brown. It is recrystallized by dissolving in 150 ml. of hot methanol, adding 1 g. of Norit, filtering, and cooling the filtrate to 0° (Note 7). The yield of yellow crystals of dibenzoylmethane, m.p. 77–78° (Note 8), thus obtained is 70–80 g. (62–71% based on the acetophenone).