Chemoselective reductions are valuable in organic synthesis and are routinely discussed in a sophomore organic chemistry course. Yet, there are few examples of laboratory experiments that illustrate such chemoselectivity. A reaction that is routinely discussed in sophomore organic chemistry is the selective reduction of aldehydes and ketones using sodium borohydride. Esters are typically not affected by NaBH4. However, none of the lab experiments reported to date illustrate this chemoselectivity (1). We have developed a discovery-oriented lab experiment that illustrates the chemoselective nature of reductions using sodium borohydride. The experiments involve the reduction of vanillin acetate (Scheme I) and methyl 4-formylbenzoate (Scheme II), using sodium borohydride, followed by product identification using 1H and 13C NMR spectroscopy. Product identification is also achieved by classical qualitative functional group tests. Hence, this lab can be easily incorporated by departments that do not have access to an NMR spectrometer. The added element of discovery ensures that student interest and enthusiasm are retained (2). Products obtained are of sufficient purity to allow analysis by spectroscopy without further purification.


Organic Chemistry