“Inorganic Polymer Flocculation Catalyst”—Polyaluminum chloride as highly efficient and green catalyst for the Friedel-crafts alkylation of bis(indolyl)methanes

Abstract

The classic inorganic polymer flocculant—polyaluminum chloride (PAC)—was used as an environmentally friendly, efficient, and recyclable catalyst in the synthesis of Bis(indolyl)methanes (BIMs) compounds for the first time. The strategy of catalysis is to use PAC as a Lewis acid, which contains different structures of Al–O polynuclear cations. These Al atoms may have a special synergistic catalytic effect for synthesis of BIMs compounds. PAC exhibits excellent catalytic activity in both solution (Yield: 95%) and solid phase (Yield: 99%). In addition, the PAC catalyst possesses outstanding stability and can be reused at least 4 times. Therefore, PAC may have wider applications in the synthesis of other organic compounds.