BENZYLATION OF AROMATICS ON ION-EXCHANGED CLAYS

The alkylation of benzene and toluene with benzyl chloride and benzyl alcohol have been investigated over a series of clays obtained by exchanging the original cations of K10 by Ti4+,Fe3+, Zr4+, Cu2+, Zn2+, Ce3+, Cr3+ and Sn2+ cations. The acidity of these solids has been determined by infra red spectrometry using pyridine as molecular probe, The acidity of K10 clays can be changed to a great extent by cation exchange and by the thermal treatments applied to the solids. The clays treated in air at 773 K show practically pure Lewis acidity, while those dried at 393 K possess Bronsted acidity. The rate of alkylation is roughly related to acidity when the substrate is benzyl alcohol, but not when benzyl chloride is used. In that case the catalysts containing reducible cations (Fe3+, Sn4+, Cu2+) exhibit high activities in spite of their low number of acid sites. It is proposed that an oxide-reduction is the first step of the reaction in that case.