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.

Graphical abstractAlCl3 was covalently bound onto cross-linked polyvinyl alcohol (CPVA) microspheres, obtaining an immobilized Lewis acid catalyst CPVA-AlCl3. During the immobilization reaction, the structure of bound AlCl3 gradually changed from the monomeric form (–AlCl2) to the dimeric form (–Al2Cl5), which gave rise to a catalytic activity enhancement.Figure optionsDownload full-size imageDownload high-quality image (100 K)Download as PowerPoint slide