Advances in liquid-phase organic reactions using heteropolyacid and clay

Zinc ion-exchanged smectite clays, particularly Fe-containing nontronite clays, were effectively applied as insoluble, readily recoverable solid acid catalysts to liquid-phase Friedel-Crafts reactions. Mesoporous montmorillonite K10 and FSM-16 catalyzed the condensation of aldehydes and pyrroles to give porphyrin precursors more efficiently than the conventional homogeneous acids such as BF, etherate. 12-Tungstophosphoric acid could be included in silica matrix by means of sol-gel technique that involves hydrolysis of ethyl orthosilicate to give an insoluble and easily separable solid acid catalyst. The silica-included heteropolyacid was thermally more stable than an ion-exchange resin catalyst such as Amberlyst-15. and catalyzed the hydrolysis of ethyl acetate in the liquid-phase more efficiently than the resin, H-ZSM-5 and even more than aqueous heteropolyacid. (C) 1998 Elsevier Science B.V. All rights reserved.