The Last(?) Word on Student Preparation of Benzalacetophenone The preparation of benzalacetophenone (BZAP) from henzaldehyde and acetophenone, a classic example' of a hasecatalyzed aldol condensation, is described in several undergraduate organic laboratory texts. The procedure usually given is a small-scale version of the standard synthesisz, which uses aqueous hydroxide as catalyst and ethanol as co-solvent. A modification involving refluxing the reaction mixture has been d e ~ c r i b e d . ~ We have developed a procedure, partly based on older work4, which rapidly affords a satisfactory yield of BZAP a t ambient temperature. Further, the initially homogeneous reaction mixture separates into two phases when reaction is complete, thus telling the student when to begin work-up. Procedure: In a 125 ml Erlenmeyer flask, 4-8 NaOH pellets (0.5-1.0 g) are dissolved in 1-1'12 ml water (no more). After addition of 20-25 ml methanol. the solution is cooled to 20-22 "C.ITwelve milliliters (0.1 mole) acetoohenone and 10 ml (0.1 mole) benzaldehvde are added with swirline. The homoeeneous mixturevellowsimmedintel'v and warms fairlvranidl;
addition, etc. The phase separation probably occurs both because (1) the reaction generates water as a product, and (2) the product BZAP is much less soluble in aqueous methanol than are the starting materials. The fact that even a small amount ofwater greatly reduces the composition range over which hydrocarbon (-like) substances and the lower alcohols are mutually soluble is of t e e b n i d importance in connection with the use of gasoline-ethanol mixtures as motor fuels.5 We point this out to students as an example of the relevance of their laboratory experience to broader technological issues. Claisen, L., Chem. Ber., 20,657 (1887). Kohler, E. P. and Caldwell. H. M., Org. Syn. d l . "01. I ( 2 n d ed.),78 (1941). Ventura, M., J. CHEM. EDUC., 51,353 (1974). Schlenk, W. and Bergmann, Ann. 463,234 (1928); Kostanecki, St. v. and Rossbach, G., Chem. Ber., 29,1492 (1896). Whitmore, F. C., "Organic Chemistry", republication of 2nd ed., Dover Publications, Ine., New York, 1961, p. 109. University of Southern California Los Angeles, 90007
418 1 Jwmal of Chemical Education
J a m e s B. Ellern
