Metalloporphyrin-Catalyzed Oxidation of 2-Methylnaphthalene to Vitamin K3 and 6-Methyl-1,4-naphthoquinone by Potassium Monopersulfate in Aqueous Solution

The metalloporphyrin-catalyzed oxidation of 2-methynaphthalene (1) by potassium monopersulfate produced mainly two naphthoquinones: 2-methyl-1,4-naphthoquinone (2) (menadione or vitamin K(3)) and 6-methyl-1,4-naphthoquinone (3). In aqueous solution and at room temperature in the presence of 5 mol % of the water-soluble metalloporphyrins MnTPPS or FeTMPS, 2-methylnaphthalene was quantitatively oxidized to quinones 2 and 3. Based on experiments performed in(18)O-labeled water and according to the "redox tautomerism" mechanism previously described for such catalysts, the oxidation to quinones is proposed to be mainly due to a cytochrome P-450-type oxygenation reaction (oxygen atom transfer), rather than a peroxidase-type oxidation (electron transfer).