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.