A Guided-Inquiry Approach to the Sodium Borohydride Reduction and Grignard Reaction of Carbonyl Compounds

Abstract

The guided-inquiry approach is applied to the reactions of sodium borohydride and phenyl magnesium bromide with benzaldehyde, benzophenone, benzoic anhydride, and ethyl benzoate. Each team of four students receives four unknowns. Students identify the unknowns and their reaction products by using the physical state of the unknown, an instructor-provided list of potential products, IR spectra of liquid unknown products, and melting points of solid unknown products. Students use their data to deduce that esters are less electrophilic than the other carbonyl compounds in this set, that Grignard reagents are more nucleophilic than sodium borohydride, and that carboxylic acid derivatives do not undergo the nucleophilic addition reactions that are characteristic of aldehydes and ketones. Using their experimental data, students are able to propose a plausible mechanism for the reaction of carboxylic acid derivatives with strong nucleophiles.