Selective ortho hydroxylation of nitrobenzene with molecular oxygen catalyzed by the H₅PV₂Mo₁₀O₄₀ polyoxometalate

Nitrobenzene was regioselectively oxidized to 2-nitrophenol with oxygen in a reaction catalyzed by the H₅PV₂Mo₁₀O₄₀ polyoxometalate. The reaction was first order in oxygen and catalyst. ¹⁵N NMR showed the interaction between nitrobenzene and the polyoxometalate. Use of labeled ¹⁸O₂, H₂¹⁸O, a competitive kinetic isotope experiment, and use of phenyl-tert-butylnitrone as a spin-trap and identification by EPR provided evidence for formation of a radical intermediate involving a selective intramolecular interaction at the ortho position due to formation of a H₅PV₂Mo₁₀O₄₀-nitrobenzene complex.