Michael Addition and Aldol Condensation: A Simple Teaching Model for Organic Laboratory A. Garcia-Ram, J. Garcia-Ram, J. V. Sinisterra, and R. Mestres Facultades de Ciencias d e Palma de Mallorca y Cbrdoba. 07071 Palma d e Mallorca, Spain Michael addition and aldol condensation are two classical reactions in organic chemistry used to achieve C-C bond formation. General discussions of these organic reactions can be found in general textbooks, but, unfortunately, there are relatively few undergraduate simple laboratory experiments to illustrate these classical and important reactions. Three experiments are presented in this paper: A) Michael addition B) Michael addition followed by aldol addition C) Michael addition followed hy aldol condensation A) Michael Addition 0
A) Synthesis of Ethyl 24 1.3diphenyl-laxo-3-propyO-3oxobutyrate (3). To a stirred solution of ehalcone' (1) (25 mmol) and ethyl acetoacetate (2) (25 mmol) in 96%ethanol (75-100 mL) is added activated catalvst , (50 . me) .. and the mixture is stirred at room temoerature for I6 h. llsually.theprudurt brginstoprer~prtateduringthr first hour. The precipitate is i>olatrdby swtion, washed with cold water, dried, and r~cr~staliiwd irom ethand Mp = 120-1 O C . ? 'l'ypcal student yields are in the 60-80% range.
9)Synthesis of 2Carboxyethyl3,5diphenyl-5hydroxicyciohexanone (4)
rt.116h
Toa stirred solution of ehalcone (1) (25mmol) and ethylacetoacetate (2) (25 mmol) in 96% ethanol (75-100 mL) is added activated barium hydroxide (500 mg), and the mixture is stirred at room temperature for 16 h. The precipitate is isolated by suction, washed with cold water3 (to dissolve the catalyst), dried, and recrystallized from ethanol. Mp = 162-4 OC.%Typical student yields are in the 50-70% range.
8) Michael Addition and Aldd Addition
C) Michael Mditlar and Aldol Cmdematlon
(PROBUS Chem. S.A.) in an oven at 2Ml OC for 3 h. The finely powdered catalyst can be stored for months in a desiccator over NaOH without noticeable Loss of activity.
A
All three experiments are easy t o carry out, and starting materials, catalyst, and the solvents used are easily available. Each reaction yields a major reaction product easy to purify by crystallization.
Preparation of Activated Barium Hydroxide The catalyst is obtained by heating commercial Ba(OH)2.8HzO
Q Synthesis of 2-CarboxyethyC3,5dlphenyl-cyclohex-59nl-one (5) Method I-from Chalcone. To a stirred solution of chalcone ( I ) (25 mmol) and ethyl acetoacetate (2) (25 mmol) in ethanol (75-100 mL) is added activated catalyst (500 mg), and the mixture is stirred at reflux for 6 h. The solution is cooled and the precipitate is isolated by suction, washed with cold water (to dissolve the catalyst), dried, and recrystallized from ethanol. Mp = 111-2 'C2 Typical student vields are in the 60-80% range. . Method 2 from (I). To stirred solution of 4 in 96% ethanol (75-100 ml., is added activated harium hydroxide (50 ~ C Iand , the mixture la rtwred at reflux f
