Checked by Charles C. Price and Wm. J. Belanger.
1. Procedure
A mixture of
35.4 g. (0.3 mole) of allylbenzene,
29.4 g. (0.3 mole) of maleic anhydride, and
50 ml. of o-dichlorobenzene (Note
1) in a
200-ml. round-bottomed flask is heated under reflux for 22 hours under an air condenser. While the orange mixture cools to 50°, the flask is equipped for vacuum distillation. At a bath temperature below 130°, the solvent and unreacted starting materials are removed by vacuum distillation with a
water pump. The boiling range is 66–72°/23 mm. The viscous residue is poured while hot into a
125-ml. sausage flask (Note
2), and the transfer is completed with small amounts of
acetone. After removal of the
acetone by vacuum distillation with a water pump, the product is distilled, b.p.
199–206°/2 mm. (bath temperature 220–270°), to give
27–35 g. (
42–54%) of a pale yellow liquid which solidifies readily (Note
3).
The product is melted in the
receiver and poured into
100 ml. of benzene. An additional
25 ml. of hot benzene is used to rinse the receiver. The
benzene solution is brought to boiling, filtered, and diluted with approximately
100 ml. of petroleum ether (60–75°) until faintly turbid. It is reheated to boiling, allowed to cool, and finally refrigerated for 4 hours. The white crystals are collected on a
Büchner funnel, washed with two
25-ml. portions of cold 1:1 benzene-petroleum ether, pressed dry, and airdried. The yield of anhydride melting at
103–105° is
24–31 g. (
37–48%) (Note
4).
The anhydride is readily hydrolyzed by boiling a mixture of
21.6 g. (0.1 mole) of anhydride,
22.0 g. (0.207 mole) of anhydrous sodium carbonate, and 250 ml. of water for 2 hours on a hot plate. The pale yellow solution is cooled and extracted with
100 ml. of isopropyl ether (Note
5). The
ether extract is washed with 50 ml. of water, and the combined water layers are acidified to Congo red by the slow addition of
10% sulfuric acid. The acid separates as an oil which quickly solidifies on cooling and stirring. It is collected on a Büchner funnel, washed with cold water, pressed dry on the funnel, and finally air-dried. The yield is
22 g. (
94% based on the anhydride), m.p.
140–143°. The acid is conveniently recrystallized from
acetonitrile (Note 6), using 5 ml. per gram of crude acid. The recovery of pure acid having a melting point of
142–143° is
85% (Note
7).
2. Notes
2. A suitable flask is prepared from a
525-ml. distilling flask by replacing the narrow side arm with a 150-mm. length of 10-mm. tubing. The side arm of a second flask is cut off to 25 mm., and the two flasks are connected by inserting the 10-mm. side arm into the bulb of the second flask.
A few boiling stones or sticks are added to the first flask containing the material to be distilled, a rubber stopper bearing a thermometer is inserted, and vacuum is applied to the shortened side arm of the receiver.
3. A
Wood's metal bath is convenient as a high-temperature heat source.
4. Once-crystallized anhydride is sufficiently pure for conversion to the acid. A second recrystallization gives pure material, m.p.
106.0–106.5°.
5.
Ethyl ether may be used. The aqueous layers must then be heated to boiling and cooled before acidification; otherwise the acid is slow to crystallize.
7. The acid is partially dehydrated near its melting point. The reported melting point was observed by immersing the capillary at 140° and heating at 2° per minute.
3. Discussion
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