Introducing Column Chromatography through Colorful Reactions of Guaiazulene

We report two related experiments to introduce column chromatography in the context of a second-year organic chemistry lab course or an upper-division advanced organic chemistry lab course. Both experiments involve functionalization of guaiazulene via electrophilic aromatic substitution, and the highly colored starting material and products serve as clear visual indicators of reaction progress and of the purification. The longer version of the experiment scaffolds the chromatography process by guiding students to develop conditions to purify their own unique compound. The products are amenable to a wide variety of characterization techniques, including UV-visible absorbance spectroscopy and 2D NMR spectroscopy. These experiments are highly flexible and have been implemented in a second-year course as an activity taking a single lab period and in an upper-division course as an activity taking three full lab periods. As judged by the results and discussion from their lab reports, students in both classes were largely successful at meeting the learning objectives for these experiments, including monitoring reaction progress using thin-layer chromatography, separating compound mixtures using column chromatography, and assessing the success of a reaction based on experimental data.