Org. Synth. 1929, 9, 38
DOI: 10.15227/orgsyn.009.0038
Submitted by C. S. Marvel and W. B. King.
Checked by Henry Gilman, R. E. Fothergill, and R. E. Brown.
1. Procedure
In a 2-l. two-necked flask fitted with a short reflux condenser and mechanical stirrer (Note 1) are placed 400 cc. of dry xylene (Note 2) and 29 g. (1.26 atoms) of clean sodium (Note 3) cut in small pieces. The flask is surrounded by an oil bath and heated until the sodium has melted. At this point the stirrer is started and the sodium is broken up into very small particles (Note 4). The oil bath is removed, but stirring is continued until the sodium has solidified in very fine particles. The xylene is then poured off, and to the sodium is added 460 cc. (4.7 moles) of absolute ethyl acetate (Note 5) containing 3–4 cc. of absolute ethyl alcohol (Note 6). The flask is quickly cooled to 0° and 106 g. (1 mole) of pure benzaldehyde (Note 7) is added slowly from a separatory funnel while the mixture is stirred. The temperature is held between 0 and 5° (Note 8). The reaction starts as soon as the benzaldehyde is added, as is shown by the production of a reddish substance on the particles of the sodium. About one and one-half to two hours are required for this addition. The stirring is continued until practically all of the sodium has reacted (one hour after all the aldehyde has been added).
When most of the sodium (Note 9) has disappeared, 90–95 cc. of glacial acetic acid is added and the mixture is carefully diluted with water. The ester layer is separated, the water layer is extracted with about 25–50 cc. of ethyl acetate, and the combined ester portions are washed with 300 cc. of 6 N hydrochloric acid and then dried with sodium sulfate. The ethyl acetate is distilled from a water bath and the remaining liquid is transferred to a Claisen flask and distilled from an oil bath under reduced pressure. A small fraction comes over below 128°/6 mm. and is discarded. The ethyl cinnamate (Note 10) boils at 128–133°/6 mm.; 168–173°/46 mm. The yield is 120–130 g. (68–74 per cent of the theoretical amount).
2. Notes
1. The stirrer must be very efficient in order to powder the sodium without splashing it onto the walls of the flask above the solvent.
2. The use of sodium powdered under xylene allows the reaction to be carried out much more rapidly than is the case if the sodium is cut into small pieces with a knife. Toluene may be used in place of xylene. The sodium should be as free as possible from oxide.
3. To obtain the maximum yield it is necessary to use slightly more than one equivalent of sodium. When exactly one equivalent is used the yield is about 60 per cent of the theoretical amount.
4. The powdered sodium may also be prepared by melting the sodium under hot xylene and shaking in a tightly stoppered flask wrapped in a heavy cloth.
5. The grade of ethyl acetate used in the preparation is very important. The absolute ethyl acetate (99.5 per cent) sold by the U. S. Industrial Alcohol Company is very satisfactory. If this grade is not available the ordinary ester may be purified by washing first with sodium carbonate solution, then with saturated calcium chloride solution and finally drying over anhydrous potassium carbonate.
6. A small amount of absolute alcohol is needed to start the reaction. When no alcohol is added the yields are consistently 55–60 per cent of the theoretical amount. When too much alcohol (10–15 cc.) is added the yields drop again.
7. Technical benzaldehyde is washed with sodium carbonate and distilled under reduced pressure with minimum atmospheric exposure before use. The material used in checking these directions boiled over a 3° range.
8. The temperature should never be allowed to go above 10° and the best yields of pure product are obtained when the temperature is kept within the limits mentioned in the procedure.
9. Usually during the reaction a certain amount of sodium is thrown on the upper part of the flask out of the reaction mixture and forms a cake. In decomposing the mixture with glacial acetic acid and water care must be taken that this sodium does not react violently and thus cause a fire.
10. During the distillation of the ester a reddish semi-solid mass sometimes appears in the flask. This mass melts down if the oil bath is heated to 220–230° and the distillation continues smoothly.
3. Discussion
Ethyl cinnamate can be prepared by the action of ethyl alcohol on cinnamic acid in the presence of hydrogen chloride or sulfuric acid,1 and by the condensation of ethyl acetate and benzaldehyde in the presence of sodium.2 The procedure described is a slight modification of that by Claisen.2

References and Notes
  1. Kopp, Ann. 95, 318 (1855); Weger, Ann. 221, 75 (1883); Brühl, Ann. 235, 19 (1886); Fischer and Speier, Ber. 28, 3254 (1895).
  2. Claisen, Ber. 23, 977 (1890); Stoermer and Kippe, Ber. 38, 3034 (1905).

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

ethyl alcohol,
alcohol (64-17-5)

calcium chloride (10043-52-4)

potassium carbonate (584-08-7)

sulfuric acid (7664-93-9)

hydrogen chloride,
hydrochloric acid (7647-01-0)

acetic acid (64-19-7)

ethyl acetate (141-78-6)

sodium carbonate (497-19-8)

sodium sulfate (7757-82-6)

benzaldehyde (100-52-7)

toluene (108-88-3)

sodium (13966-32-0)

xylene (106-42-3)

Ethyl cinnamate (103-36-6)

cinnamic acid (621-82-9)