Terpenes are a diverse class of naturally occurring compounds. We have developed an experiment for an organic chemistry laboratory course in which familiar monoterpenes are aromatized via dehydrogenation to give familiar monoterpene products. Specifically, limonene (from lemon oil), carvone (from spearmint oil) and pulegone (from catnip) are aromatized to p-cymene (from oregano and thyme), carvacrol (from oregano) and thymol (from thyme) respectively. The starting monoterpenes were dissolved in ethanol and heated via conventional reflux or microwave irradiation in the presence of Pd/C as a catalyst. The products were isolated after filtration and evaporation of solvent and then characterized using 1H-NMR and GC-MS. Thus, carvone was converted to carvacrol with excellent purity and a 90% yield. Limonene was converted to a 3:1 mixture of p-cymene and menthane with a total yield of 52%. Pulegone was converted to a 1:1 mixture of thymol and menthone which could be separated via acid-base extraction to give thymol in 46% yield.

Aromatization of fragrant monoterpenes via palladium-catalyzed dehydrogenation

249th National Meeting (2015)

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