This experiment offers a greener approach to the bromination of an alkene (stilbene), a popular exercise in the organic chemistry laboratory. Although bromination of alkenes is an important reaction in organic chemistry, the standard procedures present significant hazards in the laboratory and to the environment. In this experiment, stilbene is brominated in ethanol using a brominating agent prepared in situ by mixing hydrobromic acid and hydrogen peroxide. The solvent and reagents provide significant hazard reductions compared with previous approaches.
This synthesis is a second-generation greener synthesis that improves upon the previous method that involved the use of a safer, solid bromination reagent (pyridinium tribromide) and a more benign solvent (ethanol). The new method provides improved atom economy compared to the pyridinium tribromide method. Both the first and second generation methods reduce hazards compared with traditional brominations that use of corrosive liquid bromine and hazardous chlorinated solvents. The link to the laboratory procedure includes pre- and post-lab questions.
Summary prepared July 2006 by James E. Hutchison, Department of Chemistry at the University of Oregon.
Doxsee, K. M.; Hutchison, J. E. Green Organic Chemistry - Strategies, Tools, and Laboratory Experiments, Print 2004; pp 125-128.