Org. Synth. 1953, 33, 70
DOI: 10.15227/orgsyn.033.0070
α-PHENYLCINNAMIC ACID
[Acrylic acid, 2,3-diphenyl-]
Submitted by Robert E. Buckles and Keith Bremer
1.
Checked by T. L. Cairns and J. C. Lorenz.
1. Procedure
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).
2. Notes
1.
Benzaldehyde, suitable for this synthesis, is purified in the following way. A 60-g. (58-ml.) sample is washed with two
20-ml. portions of 10% sodium carbonate and then with water. It is then dried over
5–10 g. of anhydrous magnesium sulfate. A few small crystals of
hydroquinone or
catechol are added with the drying agent. The dry
benzaldehyde is decanted through a cotton plug into a
Claisen flask; it is distilled under reduced pressure, preferably below 30 mm.
2.
Sharples anhydrous grade triethylamine was used without further purification.
3.
The
acetic anhydride is carefully fractionated; the 137–139° fraction is collected.
4.
A simple steam-distillation apparatus such as that given by Fieser
4 is entirely satisfactory. It is usually necessary to heat the distillation flask with a
steam bath or a small flame in order to minimize the accumulation of excess water in the flask.
5.
The submitters used
5 ml. of 95% ethanol and 5 ml. of water per gram of crude product for recrystallization. The checkers found use of 3:2 ethanol:water by volume more convenient.
3. Discussion
α-Phenylcinnamic acid has been prepared by the distillation of
benzylmandelic acid,
5 by the condensation of
phenylacetyl chloride6 or
phenylacetic acid7 with
benzaldehyde in the presence of
triethylamine; by the reaction of
sodium or potassium phenylacetate with
benzaldehyde in
acetic anhydride;
8,9,10,11 and by the treatment of
ethyl α-bromo-α,β-diphenylpropionate with
potassium hydroxide.
12 The most convenient synthesis appears to be that described above.
13,14,15
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
sodium or potassium phenylacetate
ethanol (64-17-5)
hydrochloric acid (7647-01-0)
acetic anhydride (108-24-7)
hydroquinone (123-31-9)
sodium carbonate (497-19-8)
benzaldehyde (100-52-7)
decolorizing carbon (7782-42-5)
potassium hydroxide (1310-58-3)
Phenylacetic acid (103-82-2)
Catechol (120-80-9)
magnesium sulfate (7487-88-9)
phenylacetyl chloride (103-80-0)
triethylamine (121-44-8)
α-Phenylcinnamic acid,
Acrylic acid, 2,3-diphenyl- (3368-16-9)
benzylmandelic acid
ethyl α-bromo-α,β-diphenylpropionate
cis-Stilbene (645-49-8)
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