Oxidations Relevant to Industrial Processes

Various new observations, including the higher reactivity of cis-alkenes, isotope effects, and syn stereospecificity, confirm a concerted mechanism with a transition state of spiro geometry. Theoretical studies provided support to this view.1184-1188 Radical pathways were shown by computational methods and experiments to also be possible.1189,1190 

Newer studies provide numerous examples of the use of metal catalysts exhibiting high activity and selectivity in epoxidation with various oxidants mainly with H202.1201-1210 Catalysts developed by combinatorial methods1211,1212 and hetero-genized catalysts1213 were also applied. 

Highly enantioselective epoxidation of unfunctionalized alkenes was developed by using chiral metalloporphyrin catalysts.1214-1218 Remarkable anion axial ligand effects were observed with [Fe(TPFPP)X] complexes (X = triflate, perchlorate, nitrate).1219 Hexafluoroacetone was found to be an efficient cocatalyst with H202,1220 and alkenes could be epoxidized by ozone at ambient temperature.1221 

Since the porphyrin ring is liable to oxidative self-destruction and catalyst recovery is problematic, studies have focused on the development of porphyrins with 

Mechanistic studies showed that epoxidation catalyzed by MTO/H2O2 occurs as direct oxygen transfer via transition states of spiro structure likely involving both mono- and bisperoxo complexes.1233 1245-1247 

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