Sulfonated polystyrene-modified mesoporous organosilicas for acid-catalyzed processes
Organically-modified mesoporous silica materials have been prepared by direct co-condensation of styrylethyltrimethoxysilane (STETMOS) and tetraethylorthosilicate (TEOS) in one-pot synthesis. The polimerizable nature of the styryl-containing precursor induces the formation of anchored polystyrene blocks on the silica surface, which are amenable to be functionalized with acid groups via sulfonation. The resultant organosulfonic-modified mesostructured silica materials exhibit hexagonal long-range mesoscopic arrangement with extended surface areas and narrow mean pore size distributions. Upon sulfonation a high number of sulfonic acid sites have been introduced on the silica-anchored polystyrene-type organic moieties, thus providing strong acid sites embedded in a hydrophobic micro-environment. The catalytic performance of these strongly acidic hydrophobic materials has been assessed and compared with commercial catalysts in three different acid-catalyzed reactions. Two of them are acid strength-demanding reactions such as acylation of anisole with acetic anhydride and Fries rearrangement of phenyl acetate. The third one, based on the esterification of oleic acid with n-butanol, is a catalytic test wherein the hydrophobic nature of the catalyst surface plays an essential role. As result of these catalytic tests, the sulfonated polystyrene-modified hybrid materials have been shown as versatile and highly active acid heterogeneous catalysts, especially in hydrophobicity-demanding systems.
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