A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1922, 2, 1
DOI: 10.15227/orgsyn.002.0001
Submitted by E. P. Kohler and H. M. Chadwell.
Checked by H. T. Clarke and R. P. Leavitt.
1. Procedure
A solution of 218 g. (5.5 moles) of sodium hydroxide in 1960 g. of water and 1000 g. (1225 cc.) of 95 per cent alcohol are introduced into a 5.5-l. bottle which is loosely covered with a perforated disk of cardboard, supplied with an effective stirrer, and supported in a larger vessel so as to permit cooling with cracked ice. Into the alkaline solution, 520 g. (4.3 moles) of pure acetophenone (Note 1) is poured, the bottle is rapidly surrounded with cracked ice, and the stirrer started; 460 g. (4.3 moles) of u. s. p. benzaldehyde (Note 2) is then added at once. The temperature of the mixture should not be below 15° and it should not be allowed to rise above 30° during the reaction (Note 3). If it tends to do so, the stirring is not sufficiently vigorous.
It is advantageous, though not essential, to inoculate the mixture with a little powdered benzalacetophenone after stirring for one-half hour. After two to three hours, the mixture becomes so thick that the stirring is no longer effective. The stirrer is then removed and the mixture left to itself in an ice box for about ten hours. The mixture now is a thick paste composed of small shot-like grains suspended in an almost colorless liquid. It is cooled in a freezing mixture and then either centrifuged or filtered on a large Büchner funnel, washed with water until the washings are neutral to litmus, and finally washed with 200 cc. of 95 per cent alcohol, which has previously been cooled to 0°. After thorough drying in the air, the crude product weighs about 880 g. (97 per cent of the theoretical amount) and melts at 50–54°. It is sufficiently pure for most purposes but tenaciously holds traces of water. It is most readily purified by recrystallization from four to four and one-half times its weight of 95 per cent alcohol (Note 4). Eight hundred and eighty grams of crude product give 770 g. (85 per cent of the theoretical amount) of light yellow material (m. p. 55–57°) and 40–50 g. that require recrystallization.
2. Notes
1. The acetophenone should be as pure as possible (m. p. 20°). Commercial acetophenone contains variable quantities of impurities which reduce the yield. By distilling commercial acetophenone with the help of a good still-head (preferably under diminished pressure) and using only the fraction which boils at 201–202° (76–77° /10 mm.) greater quantities of benzalacetophenone can be obtained than by using the entire sample.
2. Commercial benzaldehyde can be used in place of the purer product, but the amount used must be increased to make up for the impurities which are present.
3. If the temperature is too low, or the stirring too slow, the product separates as an oil, which later solidifies in large lumps. If the temperature is allowed to rise above 30°, secondary reactions diminish both the yield and the purity of the product. The most favorable temperature is 25°.
4. In recrystallizing benzalacetophenone, the alcohol should be saturated at 50°. If the solution is saturated above this temperature, the benzalacetophenone tends to separate as an oil. The solution should be allowed to cool gradually, and should finally be chilled in a freezing mixture.
3. Discussion
Benzalacetophenone can be prepared from benzaldehyde and acetophenone, by the use of either acid1 or alkaline condensing agents. The alkaline agents are superior and those generally used are a 30 per cent solution of sodium methoxide at low temperatures2 and alcoholic sodium hydroxide.3 Preliminary experiments showed that condensation with sodium methoxide requires a long time and gives a product which is difficult to handle in large quantities.

References and Notes
  1. Claisen and Claparède, Ber. 14, 2463 (1881); Straus and Grindel, Ann. 439, 276 (1924); Breslow and Hauser, J. Am. Chem. Soc. 62, 2385 (1940).
  2. Claisen, Ber. 20, 657 (1887).
  3. Kostanecki and Rossbach, Ber. 29, 1492 (1896); Schlenck and Bergmann, Ann. 463, 234 (1928).

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

alcohol (64-17-5)

sodium hydroxide (1310-73-2)

Chalcone (94-41-7)

benzaldehyde (100-52-7)

Acetophenone (98-86-2)

sodium methoxide (124-41-4)