Oxidations catalyzed by stable metallo-tetraaryl porphyrins under aqueous-organic two-phase conditions

Factors ruling the epoxidation of internal and ofd-olefins, catalyzed by chemically stable Mn(II1)tetraaryl porphyrins and promoted by HOCl and/or C10and by 30% H 0 are investigated in order to find conditions for large scale practical application. Reactions are carried out in CH C1 -H 0 at O°C, and are greatly enhanced by the presence of lipophilic imidazoles or pyridines as axial ligands on the complexed metal. Epoxidation rates and porphyrin stabilities are largely influenced by the pH of the aqueous phase, by the ligand/porphyrin ratio (L/P), and (for HOCl/ClOpromoted reactions) by the presence of a phase-transfer catalyst. The association constants (K K ) between Mn(II1) porphyrins and the axial ligands have been evaluate5 in order to rationalize the effect of L/P's on the reaction rates. Imidazole or pyridine l'tailedl' Mn-porphyrins are very efficient catalysts. Reactions promoted by H 0 are strongly accelerated by lipophilic axial ligands and carboxylic acids, both in equimolecular amounts with respect to the porphyrin. 2 2'