Silica-occluded Heteropoly acids

Several zeolites in the II-form, two activated clays, a silica-alumina, a sulfonic acid resin and a silica-occluded heteropoly acid were tested in the reaction of cyclohcxcne and toluene (excess) at 110 °C [64]. The ortho / meta / para ratio of the mixtures strongly depends on the structure of the catalysts involved. With zeolite H-USY and Filtrol-24 as active catalysts the meta / para ratio is found to be about 2 1, in agreement with the thermodynamic equilibrium, and the ortho-isomer is essentially absent.By contrast 11-Bcta and H-mordenite gave a meta /para ratio of 1 4.5. As H-USY appeared to be a good isomerization catalyst for the cyclohexyltoluenes, the mechanism may involve ortho / para-alkylation followed by isomerization. Researchers of UOP (Dcs Plaines, USA) found a separation method for meta / para cyclohexyltoluenc (undisclosed technique). Altogether the results open a new low-waste route to 3-methylbiphenyl. 

A wide variety of solid-acid catalysts is available [17] acidic clays, zeolites, silica-occluded heteropoly acids, sulfonated polysiloxanes, Nafion (a sulfonated perfluoroalkyl resin) and Nafion-silica composites, and a variety of hybrid sulfonated mesoporous systems (see Chapter 3). 

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