Preparation, structure, and catalytic activity of aluminum chloride immobilized on cross-linked polyvinyl alcohol microspheres

Aluminum chloride was covalently bound to cross-linked polyvinyl alcohol (CPVA) microspheres, giving rise to polymer-supported Lewis acid catalysts CPVA-AlCl3 with a high loading (2.07 mmol/g). Their chemical structures were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, atomic absorption spectrometry, and chemical analysis methods. The catalytic activity of CPVA-AlCl3 as well as the relationship between structure and activity was investigated by using Friedel-Crafts acylation reaction of polystyrene. These results suggest that during the immobilization process the structure of the bound aluminum chloride gradually changed from the monomeric form (-AlCl2) to the dimeric form (-Al2Cl5). The presence of -Al2Cl5 gives rise to a catalytic activity enhancement, and the activities of various forms of CPVA-AlCl3 follow an order: CPVA-Al2Cl5 > transitional form > CPVA-AlCl2. In addition, this kind of immobilized Lewis acid catalyst has excellent recyclability and reusability, and in particular, CPVA-Al2Cl5 displayed an extremely low extent of catalyst deactivation in the repeated acylation reactions. (C) 2010 Elsevier B.V. All rights reserved.