Catalytic Reduction of Cinnamyl Alcohol by In Situ Generated H2 Gas and NMR Assessments of the Product(s)

The described laboratory experiment has been designed to introduce undergraduate students to multiple organic chemistry laboratory techniques by conducting catalytic hydrogenation of cinnamyl alcohol (E-isomer), but without the use of compressed hydrogen gas. The combination of tetrahydroxydiboron (B2 (OH) 4, a solid), a tertiary amine (4-methylmorpholine, 4-MM), and 5% Pd/C allows the harvested hydrogen gas produced in situ to reduce the olefin. This protocol allows a demonstration of this powerful addition reaction that is taught early in sophomore organic chemistry, while eliminating the hazards associated with the storage and use of compressed hydrogen gas. The key laboratory techniques incorporated, besides the reaction setup, are development and visualization of thin-layer chromatograms, column chromatography over silica-gel, and solvent extraction. For product analysis, the 1H, 13C1H, and HMQC NMR spectra of cinnamyl and the hydrogenated hydrocinnamyl alcohols have been obtained. Herein, we show two spectra of products obtained, one containing only the reduced product and the other containing an overreduction product. This provides an opportunity to discuss calculation of product ratios and to reinforce NMR spectroscopy concepts. The entire protocol would constitute activities associated with conducting a reaction, isolating, and evaluating the product. In our labs two undergraduate students, one with two semesters of undergraduate organic chemistry and the other with no prior organic chemistry laboratory experience performed the laboratory protocol and the collection and analysis of NMR data. At the end of the experiment, they were evaluated by a post-laboratory report.