Investigating a Chemoselective Grignard Reaction in an Undergraduate Discovery Lab To Predict Reactivity and Final Products

A discovery-based Grignard experiment that emphasizes several important concepts in organic chemistry is reported. The Grignard reagent from 1-bromo-4-chlorobenzene was prepared and reacted with dimethylformamide (DMF) to synthesize 4-chlorobenzaldehyde. Students were tasked with predicting halogen reactivity in the formation of the Grignard reagent, predicting the final product, and drawing a reasonable mechanism for the reaction with DMF. The Grignard reaction with tertiary amides is typically not discussed in the organic chemistry curriculum, so the students have an opportunity to apply concepts covered in lecture to a new situation. Lastly, the students experimentally verified the identity of the product using thin layer chromatography, melting point analysis, gas chromatography, IR and NMR spectroscopy, and mass spectrometry.