Imidazole-functionalized polymer microspheres and fibers–useful materials for immobilization of oxovanadium (IV) catalysts

Both polymer microspheres and microfibers containing the imidazole functionality have been prepared and used to immobilize oxovanadium(IV). The average diameters and BET surface areas of the microspheres were 322 μm and 155 m2 g−1 while the fibers were 1.85 μm and 52 m2 g−1, respectively. XPS and microanalysis confirmed the incorporation of imidazole and vanadium in the polymeric materials. The catalytic activity of both materials was evaluated using the hydrogen peroxide facilitated oxidation of thioanisole. The microspheres were applied in a typical laboratory batch reactor set-up and quantitative conversions (>99%) were obtained in under 240 min with turn-over frequencies ranging from 21.89 to 265.53 h−1, depending on the quantity of catalyst and temperature. The microspherical catalysts also proved to be recyclable with no drop in activity being observed after three successive reactions. The vanadium functionalized fibers were applied in a pseudo continuous flow set-up. Factors influencing the overall conversion and product selectivity, including flow rate and catalyst quantity, were investigated. At flow rates of 1–4 mL h−1 near quantitative conversion was maintained over an extended period. Keeping the mass of catalyst constant (0.025 g) and varying the flow rate from 1–6 mL h−1 resulted in a shift in the formation of the oxidation product methyl phenyl sulfone from 60.1 to 18.6%