Selective acylation of 1,3-dibenzyloxybenzene to 3,5-dibenzyloxyacetophenone over cesium modified dodecatungstophosphoric acid (DTP) on clay

Abstract

The Friedel-Crafts of acylation of aromatic ethers in liquid phase using solid acids is quite challenging, due to problems of deactivation. The ubiquitously used zeolites have several limitations since bulky aromatic ethers are known to deactivate them rapidly. Acylated aromatic ethers are used in a variety of industries such as pharmaceuticals and fine chemicals, perfumes and agrochemicals. In the current work, 1,3-dibenzyloxybenzene was acylated with acetic anhydride using several solid superacids to get 3,5-dibenzyloxyacetophenone, which is a very important precursor for the production of drugs for treatment of various diseases and disorders. The activities of 20% (w/w) Cs_2.5H_0.5PW₁₂O₄₀/K-10 clay, sulfated zirconia, UDCaT-5, Amberlyst-36 and Indion-130 were studied. 20% (w/w) Cs_2.5H_0.5PW₁₂O₄₀/K-10 clay was the most selective. A systematic study was undertaken to understand the reaction mechanism and catalyst functioning with Cs_2.5H_0.5PW₁₂O₄₀/K-10. The catalyst gets deactivated slowly over repeated use and this was studied independently. The adsorption of reactants and products was studied from pure component solutions and mixtures. The experimental data so generated were used to develop a model, incorporating deactivation. The model fits the experimental data very well. Further insight is provided using the model to avoid deactivation by proper selection of process parameters to get 100% selectivity.