An Aldol Condensation Experiment Using a Number of Aldehydes and Ketones Bruce A. Hathaway
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Southeast Missouri State University, Cape Girardeau, MO 63701
The aJdol condensation is an extremely useful carboncarbon bond-forming reaction in organic chemistry. The reaction is usually easy to perform, and therefore most organic laboratory texts include at least one. Two of these have been used in the organic chemistry laboratories at my institution: preparation of benzalacetophenone (1) and preparation of dibenzalacetone (2). The ease of the latter preparation led me to investigate whether it could be expanded to other aldehyde and ketone combinations. The general reaction is 0 II
2R—CHO + CH2—C—CH2 |
|
R'
R'
-
aqNaQH
>
95% ethanol
0 II
R—CH=C—C—C=CHR + 2H20 I
I
R' R' Four aldehydes and four ketones have been used (see table), which gives a total of 16 different products that can be produced. Other aldehydes and ketones were investigated
(for example, furfural and cycloheptanone), but solid prodwere not obtained in all cases; therefore, these were omitted. One main purpose for this laboratory is to encourage each student to work independently. Each student can be assigned a particular aldehyde-ketone combination. Therefore, the student will have to make his or her own observations, and make individual decisions as to which recrystallization solvent to use and how much, for example. This is a very positive aspect of this laboratory, and most students enjoy doing “their own experiment”, rather than the same ucts
anisaldehyde are quite slow. Heating a slow-reacting mixture on a steam bath for a short while will speed it up. It is important to remove all the sodium hydroxide from the crude product; hence, the washings with 95% ethanol and the acetic acid-ethanol mixture. If the sodium hydroxide is not removed, it can promote the reverse reaction during the recrystallization, thus leading to lower yields. Crude yields of the products range between 30 and 90%, depending upon which combination of aldehyde and ketone was used (see table). In most cases, the crude products are reasonably pure. Recrystallization of some products may require large amounts (200-300 mL) of solvent.
Experimental Procedure In a 125-mL Erlenmeyer flask are placed the ketone (1.0 mL), the aldehyde (4,0 mL), 95% ethanol (20 mL), and 2N aqueous sodium hydroxide (15 mL). The flask is stirred or shaken at room temperature for 15 min or until no more precipitate is observed to form. In some cases, no precipitate may have formed. These can be allowed to stand with occasional shaking or stirring (2-3 h may be required for complete precipitation), or heated on a steam bath for 15 min, then allowed to cool to room temperature. The flask is then cooled in ice, and product is collected by suction filtration. The crude product is washed consecutively with ice-cold, 10mL portions of (1) 95% ethanol, (2) 4% acetic acid in 95% ethanol, and (3) 95% ethanol. If the product is not to be recrystallized, it is allowed to dry, then it is weighed and a melting point is taken. If some or all of the product is to be recrystallized, then solubilities in 95% ethanol and toluene should be checked and the better solvent used.
Acknowledgment The author would like to thank Bjorn Olesen for helpful comments and for testing this laboratory in his class and to thank the organic chemistry students at Southeast Missouri State University, who tested this experiment and made some
everyone else is doing. A few comments on the procedure are in order. The rates of reaction vary dramatically. Reactions involving cyclopentanone or cinnamaldehyde are very fast, while those with phelpful suggestions. Melting Points (°C), Literature References (in Parentheses), and Typical Percent Yields (in Brackets) for the Products Derived from Each one
Aldehyde and Ketone Combination Ketone
0,0
01,0—CIJO
CHO
113(3)
189(7)
118(7)
[50-60%]
[60-90%]
[50-80%]
175 (4)
235-236 (8)
17 0(9)
98-99 (10)
[50-60%) 133-135(11)
[50-60%]
[60-90%]
[40-60%]
[60-90%)
129-130 (5)
212 (7)
159 (10)
141-142 (10)
[40-60%]
[60-90%]
[30-50%]
[40-50%]
144(5)
225(7)
180 (10)
163-164 (10)
[40-60%]
[60-90%]
[40-60%]
[60-90%]
Volume 64
Number 4
April 1987
367
Literature Cited Adams, R.; Johnson, J. R.; Wilcox, C. F., Jr. Laboratory Experiments in Organic Chemistry, 7th ed.; Macmillan: New York, 1979; p 354. 2. Raton, D. C. The World of Organic Chemistry; McGraw-Hill: New York, 1979; p 146. ,3. Conrad, C.; Dolliver, M. Org. Synth. 1943, 2,167. 4. Gattermann, L. Ann. 1906,347.363. 1.
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Journal of Chemical Education
Heilbron, I. M.; Buck, J. S. J. Chem Soc. 1921,119,1510. Diehl, H.; Einhorn, A. Berichte 1885,18, 2325. Vorlander, D.; Hobohm, H. Berichte 1896,29,1837. 8. Maccioni, A.; Marongiu, E. Ann. Chim. (Rome) 1958, 48, 557. 9- Vorlander, D. Berichte 1921,54,2262. 10. Wallach, 0. Chem. Zent. 1908,637. 11. Poggi, R. Atti 10th Congr. Intern. Chim. 1939,3, 298; Chem. Abs. 1939,33,9297. 5.
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