Synthesis of 5,5-Diphenyl-4-penten-2-one: A Variation on a Classic Organic Synthesis Laboratory

• Joshua P. Alber ^[1] ; Michael J. DeGrand ^[1] ; Diana M. Cermak ^[1]
  1. [1] Knox College

     Knox College

     Township of Galesburg City, Estados Unidos

     
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 88, Nº 1, 2011, págs. 82-85
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • The Grignard reaction and the addition of protecting groups are standard reactions in an organic chemistry course. Organic students learn about the “quench” step of the Grignard reaction using acid and water and the acid-catalyzed hydrolysis to remove the protecting group, yet in the lecture students find these two reactions to be confusing in their similarity. Although there are published syntheses that explore multistep synthesis utilizing a Grignard reaction and protecting groups, we have had limited success with these procedures in the lab. The multistep synthesis of 5,5-diphenyl-4-penten-2-one from ethyl levulinate includes these reactions. Ethyl levulinate, a γ-ketoester, undergoes protection with ethylene glycol to provide an acetal ester. The acetal ester is then treated with phenylmagnesium bromide, which is prepared prior to use, followed by an aqueous acid quench to produce a tertiary alcohol that can be purified by recrystallization. Finally, the acetal is removed and the tertiary alcohol undergoes dehydration under acid-catalyzed conditions to provide 5,5-diphenyl-4-penten-2-one. Students characterize their products at each stage of the synthesis using GC−MS, IR, 1H NMR, and 13C NMR spectroscopy. The three-week experiment teaches students not only about classic reactions in organic chemistry, but also the difference between quench and hydrolysis steps in a hands-on manner.