Author Contact: email@example.com
This laboratory exercise teaches students some of the principles of green chemistry while simultaneously introducing them to several traditional organic reactions. All the reagents used in the experiment are relatively safe and the avoidance of volatile organic solvents reduces cost, waste and hazards. The ultimate pyridine product is reached in three steps. The first step is the solventless aldol condensation of benzaldeyde and acetophenone. In the second step, a solventless Michael addition of 2-acetylpyridine to 1,3-diphenylpropenone is performed. Then, lastly, a ring closure is performed by heating the diketone in a solution of ammonium acetate in acetic acid. While step three is not solventless it should be noted that acetic acid has the potential of being a renewable solvent formed from the oxidation of ethanol.
The synthesis can be completed in a three hour period with final student yields ranging from 60-90%. This experiment provides an instructor with the opportunity to introduce or further reinforce the topics of green chemistry, aldol condensations, Michael additions, the Krohnke pyridine synthesis, recrystallizations, thin-layer chromatography, IR spectroscopy, carbon NMR, and diastereotopic hydrogens and their evidence in proton NMR.
Supplemental information includes a background section, experimental procedures, post-lab questions, spectroscopic information, instructor notes and tips.
Summary prepared January 2009 by Douglas M. Young at the University of Oregon.
Cave, G. W.; Raston, C. L. J. Chem. Educ., Print 2005, 82, pp 468-469.