Heteropolyacids and large-pore zeolites as catalysts in acylation reactions using α,β-unsaturated organic acids as acylating agents

Pure phosphotungstic acid (H3PW12O40), supported on SiO2 and in the form of Cesium salts have been studied as acid catalysts for the acylation of toluene, p-xylene and m-xylene with crotonic acid. Since crotonic acid can either alkylate and/or acylate the alkylaromatic compounds, it was specifically selected to study the influence of the catalyst on the selectivity for these two competing reactions. Analysis of products obtained when acylating with an α,β-unsaturated acid show that all the catalysts are more active for acylation than for alkylation. Heteropolyacids were found to be more active than zeolites H-Y and Beta, even when the activity per acid site was considered. In the case of heteropolyacids, their activity is directly related to the number of accessible Brönsted acid sites.