Multicycle Testing of P-Mo-V Heteropoly Acid Catalysts in Oxidation of Substituted Phenols

A series of valuable para-quinones, such as 2,3- and 2,6-dimethyl-1,4-benzoquinones (Me(2)BQs), were synthesized via oxidation of the corresponding 2,3- and 2,6-dimethylphenols by using homogeneous high-vanadium solutions of heteropoly acids: H11P3Mo18V8'O87 (HPA-8') and H17P3Mo16V10'O89 (HPA-10'). These catalysts were shown to be capable of interdependent and reversible change of their acid and oxidative properties, the efficient regeneration of which can be performed for 25min. The complete optimization of reaction conditions allowed one to reach the selectivity of the desired Me(2)BQs in 95-97% and shorten the oxidation time. The structural integrity of heteropoly anions present in the catalyst solutions was found to persist during the repeated performing substrate oxidation and catalyst regeneration. The catalysts showed the preservation of stability and efficiency for 25 cycles, demonstrating the prospectivity of high-vanadium heteropoly acids in oxidation of organic substances.