Steam distillation of Western red cedar leaf affords an essential oil characterized by high thujone content.  In this project, students isolate a single thujone diastereoisomer from commercially available cedar leaf oil.  Treatment of crude oil containing roughly 70% thujone, predominately (6.5:1) as (a)-thujone, with ethanolic sodium hydroxide leads to epimerization at C-4 of the ketone.  Equilibration inverts the diastereoisomeric ratio in favor (roughly 2:1) of the (�)-thujone epimer.  Selective formation of the bisulfate addition product from the (�)-isomer allows for a simple purification via filtration.  Subsequent release of the free ketone upon treatment with Na2CO3 yields highly pure (�)-thujone which is characterized and indentified using IR, MS and NMR spectroscopy.  This particular monoterpene offers the opportunity to engage students with the story, science, and folklore surrounding the notorious alcoholic spirit absinthe, the �Green Fairy�.  

Isolation and structure determination of (+)-thujone from commercially available cedar leaf oil: An upper level laboratory in natural product chemistry

239th National Meeting (2010)

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