Immobilization of transition-metal hydroxamates on polystyrene resins: Effective biomimetic heterogeneous catalysts for aerobic oxidation of ethylbenzene

Abstract

Salicylhydroxamic acid(SHA) was covalently grafted onto chloromethylated crosslinked polystyrene spheres(CMCPS) by the Friedel-Crafts alkylation reaction. The amount of SHA on CPS was found to be mainly dependent on the amount of Lewis acid(SnCl₄) used and the reaction temperature. Under optimized conditions, the amount of SHA attached to CPS could reach up to 0.43 g/g CPS. Transition metal ions[Co(II), Cu(II), Fe(III) or Mn(II)] were then introduced into the resulting SHA-functionalized microspheres(SHA/CPS) through SHA-metal ion chelation. The obtained microspheres MSHA/CPS were explored as biomimetic catalysts for the aerobic oxidation of ethylbenzene(EB) to ethylbenzene hydroperoxide(EBHP). Among the four supported metal catalysts, FeSHA/CPS showed the highest catalytic activity and good reusability, indicating its great potential as an effective heterogeneous catalyst for the aerobic oxidation of hydrocarbons under mild conditions.

Keywords

Salicylhydroxamic acid-transition metal complex / Immobilization / Crosslinked polystyrene / Catalytic oxidation / Ethylbenzene

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