Alkenes oxidation with organic hydroperoxides

The epoxidation of petrochemical alkenes is an intensely investigated oxidation reaction and in recent years numerous homogeneous catalysts have been developed for this reaction. However, so far the catalytic epoxidation of fatty compounds has been investigated only marginally. Sobczak and Ziolkowski reported on the epoxidation of oleic acid with organic hydroperoxides catalyzed by molybdenum complexes [37]. Typical homogeneous catalysts include Mo(CO)6 and Mo02(acac)2. 

The use of peroxidic oxidants in the epoxidation of alkenes has been the subject of detailed mechanistic investigations. Ti, V, Mo, and W compounds in their highest oxidation state are the most active catalysts and organic hydroperoxides are the oxidants of choice. The reaction is best carried out in non-polar solvents, such as hydrocarbons, with the exclusion of protic and polar compounds, because of their competition for coordination sites on the metal (Equation 22). The alcohol co-produced in the reaction behaves as an inhibitor retarding the epoxidation of the olefin. 

Hydrogen peroxide and organic hydroperoxides are relatively poor oxidants in the absence of radical initiators or other specific reagents. No reaction occurs with alkenes unless a reagent capable of producing electrophilic intermediates, such as a peracid or metal peroxo complex, is used. 

The majority of the titanium ions in titanosilicate molecular sieves in the dehydrated state are present in two types of structures, the framework tetrapodal and tripodal structures. The tetrapodal species dominate in TS-1 and Ti-beta, and the tripodals are more prevalent in Ti-MCM-41 and other mesoporous materials. The coordinatively unsaturated Ti ions in these structures exhibit Lewis acidity and strongly adsorb molecules such as H2O, NH3, H2O2, alkenes, etc. On interaction with H2O2, H2 + O2, or alkyl hydroperoxides, the Ti ions expand their coordination number to 5 or 6 and form side-on Ti-peroxo and superoxo complexes which catalyze the many oxidation reactions of NH3 and organic molecules. 

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