By Shawn Postle, Member-at-Large for the GCI
The Chemistry Teaching Fellows Program (CTFP) at the University of Toronto gives senior graduate students the opportunity to gain pedagogical experience by developing new educational content for undergraduate students within the chemistry department.
I recently had the opportunity to complete a CTFP project in collaboration with Dr. Barb Morra where we designed a new laboratory experiment for CHM 151Y, a first year organic chemistry course. The experiment that we aimed to replace involved the concurrent hydrogenation/dehydrogenation of cyclohexene using a palladium catalyst, to form cyclohexane and benzene. There were two main concerns with this experiment: the use and generation of carcinogenic and toxic chemicals, and the efficacy of a simple demonstration of alkene reactivity due to the lack of qualitative observations that could be made to differentiate the products from the starting material.
To address the shortcomings of the old experiment, we had three goals in mind while designing the replacement experiment: 1) to reinforce concepts of alkene chemistry learned in lecture, 2) to emphasize the importance of sustainable chemistry, and 3) to introduce thin-layer chromatography.
The L-proline catalyzed cyclization of L-linalool was an ideal reaction for satisfying these three criteria. In the lecture component of the course, students learn about electrophilic addition reactions of alkenes, such as halohydrin formation (Scheme 1a). For the experiment, we chose an intramolecular variation to show this same type of reactivity. The reaction carried out in the lab is the cycloetherification of L-linalool (Scheme 1b).
Students also perform thin-layer chromatography to verify that all of their starting material has been consumed. Thin-layer chromatography is an ideal technique for first year students, as it is a relatively simple method of analysis to understand and carry out.
In this new experiment, students are introduced to the 12 principles of green chemistry. We draw their attention to specific examples from the reaction to illustrate different principles. L-linalool, a terpene alcohol, is derived from renewable resources (principle #7). The reaction is catalyzed by innocuous L-proline, which reduces the reaction time from two days to a few minutes (principle #9). N-bromosuccinimide (NBS) is a safer alternative to elemental bromine as a source of electrophilic bromine (principle #4). Moreover, students are directed to the GlaxoSmithKline safer solvent guide to compare the properties and environmental impact of the solvent used to those employed in older cycloetherification reactions (principle #5). This gives students insight into how the 12 principles of green chemistry can be effectively applied with just a simple substitution.
Some of the 12 principles of green chemistry are fundamentally easy to understand, even for a first year student, but others require more chemistry background. It is through repeated exposure to these ideas that students can gain a fuller appreciation of their importance. Introducing students to the concept of sustainable chemistry throughout their chemistry education in a variety of courses helps students understand that green chemistry is not something separate from organic, inorganic, analytical or any other type of chemistry, but is rather a philosophy that can always be implemented.