Rescuing student learning outcomes from the organic waste container

Session: Undergraduate Research Posters: Organic Chemistry:  

A perennial frustration for students and faculty alike is the “make it and dump it” cycle characteristic of some second-year undergraduate organic chemistry laboratories. We seek to change this paradigm by rescuing student products and by-products from the waste container and using them to extend student learning outcomes either in an enriched second-year experience or in an upper-division undergraduate course. This poster demonstrates the new paradigm in a classic Claisen-Schmidt condensation, the base-catalyzed formation of 4-methoxychalcone (p-anisalacetophenone) from 4-methoxybenzaldehyde (p-anisaldehyde) and acetophenone. One appeal of this reaction is that the desired product precipitates from the reaction mixture and is readily isolated by vacuum filtration. The filtrate is typically discarded as waste. However, analysis of this filtrate by thin-layer chromatography on silica gel plates resolved with 4:1 hexanes:ethyl acetate reveals, in addition to the expected 4-methoxychalcone (Rf = 0.54), a prominent peak at a lower Rf value (0.41). Students may be set to the task of performing the isolation of this unknown species and elucidating its structure using NMR spectroscopy. In addition, students may propose a mechanism for the formation of this by-product that turns out to be a Michael adduct. In summary, a by-product normally sent to the waste container is repurposed, with the net effect of extending the learning outcomes of the laboratory. A new protocol will be presented, suitable for either the second-year or upper-division undergraduate laboratory.