Vanadium-based polyoxometalate complex as a new and efficient catalyst for phenol hydroxylation under mild conditions

Abstract

An eco-compatible catalytic protocol for H₂O₂ induced hydroxylation of phenol (PH) to catechol (CT) and hydroquinone (HQ) in aqueous medium, using a polyoxovanadate (POV) complex as the catalyst, is described. The synthesis of the POV catalyst, with a new type of three dimensional framework, Na₆(H₂O)₂₂(V₁₀O₂₈)·2H₂O (1) was accomplished by establishing a non-hydrothermal one-step methodology under mild conditions. The catalyst was characterized by elemental analysis, spectral studies, single crystal X-ray diffraction studies, and Brunauer–Emmett–Teller (BET) and TGA analysis. Under optimum conditions of reaction, conducted at ambient temperature, the phenol conversion reached up to 55.4% providing a TON of 138. The catalyst could be recovered easily and recycled at least up to three cycles without significant change in activity. The developed methodology is operationally simple and free from halogenated solvents or any other hazardous additives.