V-, Mo- and W-containing layered double hydroxides as effective catalysts for mild oxidation of thioethers and thiophenes with H2O2

Catalytic oxidation of thioethers and thiophene derivatives with H₂O₂ was performed at 40 °C and atmospheric pressure, in presence of W-, V- and Mo-containing layered double hydroxides (LDH). The catalysts were prepared by direct ion exchange with metal-oxoanions, i.e. WO₄²⁻, W₇O₂₄⁶⁻, V₂O₇⁴⁻, V₁₀O₂₈⁶⁻, MoO₄²⁻ and Mo₇O₂₄⁶⁻, of the LDH containing aluminum and magnesium atoms in the brucite layer. All the catalysts showed good activity and selectivity in the sulfoxidation reaction, but the catalyst performances strongly depended on the nature of the anion species intercalated in the interlayer gallery. Thus, the W-based LDH was more active and more stable than the V-LDH and Mo-LDH catalysts. The conversion of sulfur-containing compounds is also dependent on the nucleophilicity of substrates and the following order of reactivity was observed benzothiophene < dibenzothiophene < diphenyl-sulfide < benzyl-phenyl-sulfide < methyl-phenyl-sulfide.