Resumen de Regiospecific Epoxidation of Carvone: A Discovery-Oriented Experiment for Understanding the Selectivity and Mechanism of Epoxidation Reactions
Kendrew K. W. Mak, Y. M. Lai, Yuk-Hong Siu
This article describes a discovery-oriented experiment for demonstrating the selectivity of two epoxidation reactions. Peroxy acids and alkaline H2O2 are two commonly used reagents for alkene epoxidation. The former react preferentially with electron-rich alkenes while the latter works better with α,β-unsaturated carbonyl compounds. The selectivity of these two reagents on carvone, a naturally occurring compound that contains both types of C=C bonds, was investigated. The product mixtures obtained from the two different reactions were analyzed by thin-layer chromatography and 1H NMR spectroscopy. Both of the reactions were found to be regiospecific. The selectivity was attributed to the roles played by the alkene C=C bonds, which act as a nucleophile in the peroxy acid epoxidation but as an electrophile in the alkaline H2O2 reaction. The discovery-oriented approach is aimed at strengthening students' knowledge of the relationship between the reaction selectivity and the mechanisms.
