The system composed of manganese (2,6)-dichlorotetraphenyl- or pentafluorotetraphenyl-porphyrins, bearing nitro groups at the beta-pyrrolic positions as catalysts and monoperoxyphthalic acid magnesium salt (MMPP) as oxidant is an efficient model system for epoxidation of dodecene-1 and propene. A comparison with the corresponding system based on iron and cobalt complexes as well as the influence of the addition of a nitrogenous base are also described.