Merrifield resin supported peroxomolybdenum(vi) compounds: recoverable heterogeneous catalysts for the efficient, selective and mild oxidation of organic sulfides with H2O2

Abstract

We have generated new heterogeneous catalysts by immobilizing dioxomonoperoxomolybdenum(VI) on amino acid functionalized Merrifield resin, which exhibit excellent activity, stability and selectivity for the oxidation of thioethers and dibenzothiophene (DBT) to the corresponding sulfoxides or sulfones by H₂O₂ at ambient temperature. The synthetic protocols are high-yielding, halogen-free, environmentally clean and safe, and operationally simple. The catalysts, [MoO₂(O₂)(L)₂]²⁻-MR [L = valine (MRVMo) or alanine (MRAMo) and MR = Merrifield resin] were prepared by reacting H₂MoO₄ with 30% H₂O₂ and the respective amino acid functionalized resin, at near neutral pH. The compounds were characterized by elemental analysis, spectral studies (FTIR, Raman, ¹³C NMR and ⁹⁵Mo NMR, diffuse reflectance UV-Vis and XPS), SEM, EDX, XRD, Brunauer–Emmett–Teller (BET) and TGA-DTG analysis. The easy recyclability of the catalysts for several catalytic cycles without change in activity and selectivity, their complete chemoselectivity towards the sulfur group of substrates bearing other oxidation prone functional groups, are important “green” attributes of these catalysts.