This article describes a discovery-oriented experiment for demonstrating the selectivity of two epoxidation reactions. Peroxy acids and alkaline H 2 O 2 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 1 H 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 H 2 O 2 reaction. The discovery-oriented approach is aimed at strengthening students' knowledge of the relationship between the reaction selectivity and the mechanisms.
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Mak et al. (2006) studied this question.