The Evolution of a Green Chemistry Laboratory Experiment: Greener Brominations of Stilbene

Abstract

We describe two new greener alkene bromination reactions that offer enhanced laboratory safety and convey important green chemistry concepts, in addition to illustrating the chemistry of alkenes. The two alternative reactions, one involving pyridinium tribromide and a second using hydrogen peroxide and hydrobromic acid, are compared to the traditional bromination of stilbene through the application of green metrics, including atom economy, percent experimental atom economy, E factor, and effective mass yield. The use of these metrics to guide experiment evaluation and optimization in the teaching lab environment is examined. The development of these new experiments provides (i) an ideal case study for demonstrating the process of on-going evaluation and modification of experiments that leads toward more environmentally benign educational materials for the undergraduate organic teaching laboratory and (ii) a concrete example useful for introducing the practical use of metrics to students as a part of their laboratory experience. A green debromination procedure is also described that allows for simple and economical recycling of the starting material.