Heteropoly acids as oxidation catalysts in synthesis of K-vitamins

Mo-V-phosphoric heteropoly acids of the Keggin structure H3+nPMo12-nVnO40 (HPA-n) and their acidic salts were found to be efficient catalysts for 2-methyl-1-naphthol (MN) oxidation by dioxygen to 2-methyl-1,4-naphthoquinone (menadione, or vitamin K-3). The reaction occurs in two steps: (1) HPA-n reduction by MN followed by the product isolation; (2) HPA-n regeneration by dioxygen. For reaction MN + HPA-n, carried out in a two-phase 'water + organic' solvent system, it has been studied how the HPA-n composition and reaction conditions affect the HPA-n selectivity and activity. The reaction mechanism and methods of increasing the catalyst selectivity are suggested. The reaction has been used in scope of a new environmentally harmless technology 'Vikasib' producing the K-group vitamins.