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Abstract: Novel Lewis acid catalysts were prepared from sulfonated carbon/silica composites derived from starch and silica by treatment with Lewis acids AlCl3, SbCl3, Bi(NO3)3, ZnCl2 and FeCl3. The catalytic activity of the Lewis acids was evaluated for one-pot synthesis of 1,2,4,5-tetrasubstituted imidazoles, 3,4-dihydropyrimidin-2(1H)-ones and for Michael addition of indole to α,β-unsaturated ketones. Different Lewis acids were investigated with a view to select the most effective solid Lewis acid for organic synthesis. All the Lewis acid catalysts were characterized by FTIR, XRD and AAS analysis and the most active catalyst CSC-Star-SO3-AlCl2 was also characterized by TGA, SEM and TEM. [Copyright &y& Elsevier]

Amorphous carbon-silica composites bearing sulfonic acid derived from inexpensive natural organic compounds (glucose, maltose, cellulose, chitosan and starch) were prepared by partial carbonization followed by sulfonation and their catalytic activity was evaluated for the protection of aldehydes as 1,1-diacetates and for N-, O- and S-acylations under solvent-free conditions. Different biomaterials have been chosen, with a view to select the most active solid acid catalyst. Carbon-silica composites were characterized by FTIR, XRD and elemental analysis. Sulfonated carbon-silica composite derived from starch was found to be the most active and could be recycled for several runs without loss of significant activity. It was also characterized by TGA, SEM and TEM. [ABSTRACT FROM AUTHOR]