Selective benzoylation of o-xylene to 3,4-dimethylbenzophenone using various zeolite catalysts

The liquid phase benzoylation of o-xylene with benzoyl chloride (BOC) over various zeolite catalysts is studied in a batch reactor at atmospheric pressure and 411 K. The results obtained over different zeolite catalysts are compared with the homogeneous Lewis acid catalyst, AlCl3 and amorphous silica-alumina. The protonic form of zeolite beta is found to be an efficient catalyst compared to other zeolites in the benzoylation of o-xylene. The conversion of BOG, turnover rate of BOC conversion (TOF) and selectivity for 3,4-dimethylbenzophenone (3,4-DMBP) over zeolite H-beta are found to be 52.8 wt.%, 69.7 x 10(-5) s(-1) mol(-1) Al and 94.7 wt.%, respectively, at the following reaction conditions [H-beta to BOC (w/w) = 0.28, o-xylene to BOC (molar ratio)= 5; 411 K; 1 atm]. The non-shape selective AlCl3 catalyst produces higher amount of consecutive products (16.2 wt.%) and hence gives lower selectivity for 3,4-DMBP (76.5 wt.%). The acidity and pore structure of H-beta appeared to be responsible for good performance. increase in reaction time, catalyst concentration, reaction temperature, o-xylene to BOC molar ratio enhances the conversion of BOG, whereas it decreases with the increase in degree of Na-exchange and SiO2/Al2O3 molar ratios of H-beta. The zeolite H-beta is recycled three times without the loss of 3,4-DMBP selectivity but with a decline in the catalytic activity of H-beta. Additionally, the benzoylation of m-xylene and p-xylene is also investigated using H-beta. The Friedel-Crafts acylation reaction mechanism involves the formation of an electrophile (C6H5CO+) over an acidic zeolite catalyst which attacks the xylene ring resulting in the formation of dimethyl benzophenones. (C) 1999 Elsevier Science B.V. All rights reserved.