In a
500-ml. round-bottomed flask are placed
40.5 ml. (42.4 g., 0.40 mole) of freshly purified benzaldehyde (Note
1),
54.6 g. (0.40 mole) of phenylacetic acid,
2 40 ml. of anhydrous triethylamine (Note
2), and
80 ml. of acetic anhydride (Note
3). The mixture is boiled gently under reflux for 5 hours. After the heating period is over, the 500-ml. flask containing the reaction mixture is incorporated into a steam-distillation apparatus (Note
4). The reaction mixture is distilled with steam until the distillate coming over is no longer cloudy, and then about 50 ml. more of the distillate is collected. The distillate can be discarded. The aqueous residue is cooled, and the solution is then separated from the solid by decantation. The solid is dissolved in
500 ml. of hot 95% ethanol, and 500 ml. of water, including the solution originally decanted from the crude solid, is added to the hot solution. The mixture is heated to boiling, and
2 g. of decolorizing carbon is added. The hot solution is filtered, and the filtrate is immediately acidified to Congo red with
6N hydrochloric acid. The solution is cooled, and the resulting crystals are removed from the mixture by filtration. The yield of crude
α-phenylcinnamic acid (m.p. around
161–165°) is
60–67 g. The product is purified by crystallization from aqueous
ethanol (Note
5). The over-all yield of purified product, m.p.
172–173°, is
48–53 g. (
54–59%). The product is the isomer with the two phenyl groups
cis to each other since decarboxylation yields
cis-stilbene3 (see
p. 857).