Alkali metal salts and ammonium salts of Keggin-type heteropolyacids as solid acid catalysts for liquid-phase Friedel-Crafts reactions Original Research Article

The possibility of using a heteropolyacid salt as solid acid catalyst for liquid-phase Friedel-Crafts reactions was investigated through extensive examinations on various kinds of the salt prepared from different combinations of Keggin anions and their counter cations including ammonium ion. The catalytic behavior of the salt was discussed in relation to acidity, surface area, porosity, and thermal stability. Of the different kinds of insoluble acidic salt, K, Rb, Cs, and ammonium salts were mesoporous materials with large surface area (50–170 m2 g−1), strong acidity (H0 < −8.2), and large pore volume (0.3–0.5 ml g−1). Particularly, K2.5H0.5PW12O40, Rb2.5H0.5PW12O40, Cs2.5H0.5PW12O40, Cs2.5H0.5PMo12O40, K2H2SiW12O40, Cs2H2SiW12O40, and (NH4)2HPW12O40 worked as efficient solid acid catalysts for liquid-phase Friedel-Crafts alkylation of benzene with benzyl chloride, and some of them could also be effectively applied to the acylation of p-xylene with benzoyl chloride or benzoic anhydride. The salt catalysts were much more active than HY, LaY, Nafion-H and Zn-promoted montmorillonite.