Oxidation of Styrene Catalyzed by Recyclable Polystyrene-Supported Pyrrole-2-Carboxaldehyde Metal Catalysts

Polymer-supported heterogeneous catalysts were synthesized by anchoring pyrrole-2-carboxaldehyde on amino-methylated polystyrene and then loading V(IV), Mn(II), Ni(II) and Cu(II) ions on it. The resulting catalysts were characterized by CHNS analysis, FTIR, EDX, DRS, ESR and AAS spectral study confirming the successful immobilization of the metal complexes. The catalytic activity and selectivity of the polymer-supported catalysts were analyzed for the liquid phase oxidation of styrene mediated by H2O2 and tert-butyl hydroperoxide. The influence of reaction time, temperature and concentration of the catalyst for the oxidation of styrene were examined under optimal conditions (0.1 g catalyst; 6 h reaction time and 60 ºC temperature). A conversion rate of 96.5% was accomplished using a copper catalyst employing H2O2 as oxidant, while a selectivity of 90.1% for benzaldehyde formation was reached with a nickel catalyst utilizing tert-butyl hydroperoxide (TBHP) as oxidant. The mechanism of the oxidation of styrene in the presence of synthesized catalyst has also been proposed. The catalysts were recovered by simple filtration and reused four times without any significant loss in their activity, proving their truly heterogeneous nature.