Summary and Perspective on the Reactivity Results

Previous tables concentrated on reactivity results with typical molecules for comparison purposes. A summary of the reactivity patterns and general conditions is provided in the following (Table 1.11). 

Some generalized comments can be made concerning the various systems. Deviations from these generalizations, which can be seen in some of the results in the table, indicate exceptional behavior and are noteworthy. 

In general, since epoxidation involves electrophilic reagents, double bonds with electron-donating substituents are more reactive. Thus, internal or cyclic alkenes give higher conversions than do terminal olefins. Conversely, in general, electron-withdrawing substituents increase the activity of electrophilic catalysts. 

In general, planar-type catalysts like Mn (salen) or porphyrins favor epoxidation of czs-substituted olefins, while nonplanar complexes can carry out epoxidation of frans-substituted olefins, even when four-coordinate. 

The most effective solvents for H2O2 are polar, noncoordinating, nonbasic, and inert under oxidizing conditions [192]. Water-immiscible solvents have the advantage of minimizing hydrolysis of epoxides, but can result in mass transfer limitations with aqueous hydrogen peroxide. 

---