The mechanistic aspects in hydroxylation reactions catalyzed by fluorinated porphyrins of manganese and iron: Role of aqueous phosphate

The role of aqueous phosphate in the selective hydroxylation of cyclohexane to cyclohexanol (60–68% yields) and cyclohexene to 2-cyclohexene-1-ol (98% yield) has been discussed. Fluorinated porphyrins of manganese and iron were used as catalysts in acetonitrile with aqueous-K2HPO4 and t-BuOOH as co-catalyst and oxidant, respectively. The generation of the oxo-manganese reactive intermediate was identified by 1H, 19F NMR, EPR, UV–Vis and mass spectral studies. The formation of phosphate adduct of the oxo-manganese reactive intermediates has been proposed on the basis of high binding constant of dipotassium hydrogen phosphate with the catalyst.

Graphical abstractIn a reaction where TPFPPMnIIICl or TPFPPFeIIICl were the catalysts and t-BuOOH was the oxidant in CH3CN containing micro quantity of an aqueous-K2HPO4, the selective hydroxylation of cyclohexane and cyclohexene in remarkably high yields has been achieved. The probable mechanism of this unusual reaction has been demonstrated.Figure optionsDownload full-size imageDownload as PowerPoint slide