Phosphomolybdovanadic acid catalyzed oxidation of 2,6-dimethylphenol into para-quinone in a biphasic system

In this paper, we disclose the results of our extended investigations on the reactivity of modified-type vanadium-containing heteropoly acids H a P z Mo y V x ′ O b (HPA-x′) towards the oxidation of 2,6-dimethylphenol (2,6-Me 2 P). This reaction is of great value as an effective way to the corresponding 2,6-dimethyl-1,4-benzoquinone (2,6-Me 2 BQ), practically avoiding the formation of diphenoquinone, which is interesting from the standpoint of its potential application as a sensitizer and ‘platform molecule’. The overall process is based on two reactions: the oxidation of 2,6-Me 2 P by V V O 2 + ↔ V V - HPA and the oxidation of reduced V IV -HPA ↔ V IV O 2+ by dioxygen to the initial state. Special attention was given to the former process with regard to the influence of the reaction parameters on the product distribution. The desired quinone was efficiently synthesized in good yield (95%) at total substrate conversion, carrying out the oxidation in a biphasic water–trichloroethene system at 70 °C under nitrogen atmosphere in the presence of HPA-10′ solution (H 17 P 3 Mo 16 V 10 O 89 ). The increase in vanadium content favored the selectivity of 2,6-Me 2 BQ due to faster electron transfer. The multicycle tests of catalyst showed its stability to V 2 O 5 ·nH 2 O deposition.