Porphyrin LB film as a catalyst for alkene epoxidation

A synthetic iron ortho-substituted tetradecylpyridyl porphyrin was used to prepare Langmuir-Blodgett films. Better spreading at the gas-liquid interface was obtained for mixed films using palmitic acid in a 1:4 proportion. The minimum area per molecule from π-A curves for the pure porphyrin monolayers is correlated to the value obtained for the flat orientation of the porphyrinic center on the water surface, as determined by the CPK model. The fatty acid causes a decrease in the porphyrin minimum area per molecule. Single monolayer LB deposition gives a monomeric film without the presence of aggregates as attested by UV-visible spectra. The film was used in the heterogeneous catalysis of cyclohexene oxidation furnishing a yield two times higher than that obtained for the homogeneous system, using the same porphyrin amount and reagent ratio. The reaction was highly selective: only cyclohexene oxide was recorded as the product, confirming that the system is a good model for cytochrome P450.