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It is well known that epoxides can undergo rearrangement to yield carbonyl compounds in the presence of a Lewis acid catalyst. Classically these catalysts have included a wide variety of compounds some of which are hazardous and harmful. The impetus for this experiment came from a previous lab taught by the authors in which toxic, corrosive boron trifluoride etherate was used to catalyze the rearrangement of trans-stilbene oxide. In this greener version, bismuth triflate is used at the catalyst because it is non-toxic, inexpensive and easy to work with.
The use of a much safer Lewis acid catalyst is only one of the many green aspects of this experiment. Not only are rearrangements inherently very atom economical, but the reaction is performed on the micro-scale which decreases the amount of waste the lab generates. Also, the reaction is performed in d-chloroform which allows for the reaction mixture to be directly transferred to an NMR tube (no work-up is required) for characterization.
Subjects that can be taught alongside this lab include the prediction of NMR spectra, migratory aptitude, epoxide chemistry, Lewis acids and catalysis.
Supplemental information includes instructor notes, a student handout and spectral information.
Summary prepared January 2009 by Douglas M. Young at the University of Oregon.
Christensen, J. E.; Huddle, M. G.; Rogers, J. L.; Yung, H.; Mohan, R. S. J. Chem. Educ., Print 2008, 85, pp 1274-1275.