Mechanistic studies of olefin epoxidation by a manganese porphyrin and hypochlorite: an alternative explanation of saturation kinetics

The catalytic epoxidation of olefins with Mn(TMP)Cl with phase-transfer catalysis and hypochlorite has been reexamined from the point of view of material balance and stability of this system in the presence of three axial ligands. The efficiency (yield of epoxide formation based on OCl{sup {minus}} consumed) is found to fall off with decreasing olefin concentration and to be influenced by the nature of the axial base. With t-BuPy as the axial ligand, the stirred system in the absence of olefin is found to be stable over prolonged periods and does not lose OCl{sup {minus}} titer. This leads to the conclusion that, in the presence of low olefin concentration, the missing OCl{sup {minus}} equivalents must be consumed in a side reaction with the olefin. It is proposed that extensive byproduct oxidations account for loss of OCl{sup {minus}}, low efficiency, and apparent saturation kinetics they previously reported.