Acylation of veratrole by acetic anhydride over Hβ and HY zeolites -: Possible role of di- and triketone by-products in the deactivation process

The acylation of veratrole (1,2-dimethoxybenzene) by acetic anhydride in the presence of HY and Hbeta zeolites was carried out at 90degreesC in a batch reactor. The reaction led to acetoveratrole (3,4-dimethoxyacetophenone) selectively. HY was more active than Hp by a factor of about 1.5. Soxhlet extraction with methylene chloride of the catalyst recovered after reaction made it possible to eliminate approximately 80% of the organic material remaining on the catalyst. After soxhlet extraction the catalyst samples were dissolved with HE In addition to veratrole and acetoveratrole the organic residue obtained by this procedure contained di- and triketones as well as cyclization products. These compounds were suspected to contribute to the irreversible deactivation of the catalysts. The IR analysis of the zeolite samples after adsorption of the diketone in the presence of veratrole as well as the acylation of the latter in the presence of the diketone confirmed that this compound took part in the deactivation of the catalysts. This conclusion was also supported by the analysis of the composition of the material remaining strongly adsorbed or entrapped in the zeolites after experiments of various durations., However, the IR spectra of the catalysts after soxhlet extraction showed that another compound at least was also responsible for the deactivation of the zeolites, specially of Hp. However this compound, presumably a triketone resulting from the C-acylation of the diketone, was only stable when entrapped in the zeolitic material. It could not be synthesised and isolated by conventional means. (C) 2002 Elsevier Science B.V. All rights reserved.