Eighteen hundred milliliters of benzene (Note 1) and 350 g. of finely ground anhydrous aluminum chloride (2.6 moles) (Note 2) are placed in a 3-l. three-necked flask, fitted with a mechanical stirrer, a dropping funnel (Note 3) containing 153 g. (1 mole) of fumaryl chloride (p. 422), and a reflux condenser (Note 4). A trap for absorbing hydrogen chloride is attached to the condenser.

The mixture is well stirred and heated externally by hot water (50–60°) (Note 5), the water removed, and the fumaryl chloride admitted at a brisk rate, moderated only enough to avoid a too rapid evolution of hydrogen chloride; this requires 15–25 minutes (Note 6) and (Note 7). The mixture turns dark red and soon reaches the boiling point; hydrogen chloride is rapidly given off. The mixture is then refluxed gently for 10 minutes with stirring.

The pasty red mixture is then poured portionwise upon 4 kg. of cracked ice to which has been added 75 ml. of concentrated hydrochloric acid, the reaction mixture being thoroughly stirred before each pouring so that the aluminum chloride complex does not settle out and become concentrated at the bottom of the flask. The residue in the flask is decomposed by adding some of the ice and water. After standing 20–30 minutes, very hot water (Note 8) is added to melt any ice or frozen benzene and raise the temperature generally. The bulk of the aqueous layer is discarded by drawing it off with a glass tube connected to a suction flask. The benzene layer is next washed at least four times with hot water (Note 8) and (Note 9). Finally the warm benzene layer is transferred to a large separatory funnel, any crusts of dibenzoylethylene adhering to the various pieces of apparatus are dissolved in hot benzene, and the solutions combined; the small water layer is separated and discarded (Note 10). The hot benzene layer is then filtered, either by gravity using a large glass funnel or by suction on a Büchner funnel, into a 3-l. round-bottomed flask. After a few porcelain chips have been added, the bulk of the solvent is distilled, using a steam or boiling water bath. Most of the residual solvent is removed under diminished pressure, using a water pump, and heating until the syrupy liquid begins to crystallize suddenly (Note 11). At this point, the heating and suction are discontinued and 125 ml. of 95% ethanol is added rapidly, stirring with a wooden paddle to break up any lumps. The flask is cooled a few minutes under the tap, and the bright yellow product is collected on a 127-mm. Büchner funnel. The solid is triturated on the funnel with cold ethanol for 10 minutes to remove adhering mother liquor, and sucked as dry as possible. The yield is 186–197 g. (78–83%) (Note 11), and the melting point is 109–110° (Note 12) and (Note 13).