In a 1-l. three-necked round-bottomed flask fitted with a mercury-sealed stirrer and a reflux condenser are placed 34 g. (0.347 mole) of maleic anhydride (Note 1) and 175 g. (200 ml., 2.24 moles) of dry, thiophene-free benzene. Stirring is started, and, when the maleic anhydride has dissolved, 100 g. (0.75 mole) of anhydrous reagent grade aluminum chloride powder is added in 6–8 portions through the third neck of the flask at a rate so that the benzene refluxes moderately. The addition requires about 20 minutes. The mixture is then heated under reflux on a steam bath and stirred for 1 hour. The reaction flask is cooled thoroughly in an ice bath, a 250-ml. dropping funnel is attached to the third neck, and the mixture is hydrolyzed by adding 200 ml. of water with stirring and cooling (the first 50 ml. during 15–20 minutes and the balance in about 10 minutes), followed by 50 ml. of concentrated hydrochloric acid (Note 2). Stirring is continued for an additional 40 minutes, during which time it may be necessary to use a spatula to scrape adhering particles of the red-brown aluminum chloride addition compound from the walls of the flask.

The hydrolyzed mixture is transferred to a 1-l. Claisen flask, the transfer of material being completed by rinsing with about 50 ml. of warm water. The flask is heated in a water bath at 50–60°, and the benzene and some water are distilled at 20–30 mm. pressure (Note 3). While the residue is still molten, it is transferred to a 1-l. beaker, and the flask is rinsed with 50 ml. of warm water. After standing at 0–5° for 1 hour, the yellow solid is collected on a suction filter and washed with a solution of 25 ml. of concentrated hydrochloric acid in 100 ml. of water and then with 100 ml. of water. The washing is done most efficiently by suspending the solid in the wash liquid, cooling to 0–5° with stirring, and then filtering with suction. The preparation should not be interrupted before this point (Note 3), at which stage the crude acid may be air-dried overnight at room temperature if desired. The crude product is dissolved in a solution of 40 g. of anhydrous sodium carbonate in 250 ml. of water by warming to 40–50° (Note 4), 2 g. of Celite or other filter aid is added, and the solution is filtered with suction while warm. After the filter has been washed with two 30-ml. portions of warm water, 2 g. of Norit is added to the combined filtrates and the mixture is heated at 40–50° for 10–15 minutes with frequent stirring, then filtered with suction. The clear, yellow filtrate is transferred to a 1-l. beaker and cooled to 5–10°, and 70 ml. of concentrated hydrochloric acid is added dropwise with stirring. Efficient cooling and stirring are necessary to avoid the precipitation of the acid as an oil. After being cooled to 0–5°, the mixture is filtered with suction; the solid is washed with two 50-ml. portions of cold water and then is dried at 50° for 12–36 hours to give 56–63 g. of light-yellow anhydrous β-benzoylacrylic acid, m.p. 90–93° (Note 5). The crude acid may be crystallized from benzene, using 12–15 ml. of benzene per 5 g. of acid and cooling at 5–10° (Note 6) to give 44–47 g. of β-benzoylacrylic acid, m.p. 94–96° (Note 7). Concentration of the filtrate to one-fourth to one-fifth of its original volume gives an additional 3–6 g., melting in the range 92–96°. The total yield is 49–52 g. (80–85%) (Note 8).