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

Abstract

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, AlCl 3 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 BOC, 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.%, 69.7×10 −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 AlCl 3 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 BOC, whereas it decreases with the increase in degree of Na-exchange and SiO 2/Al 2O 3 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 (C 6H 5CO +) over an acidic zeolite catalyst which attacks the xylene ring resulting in the formation of dimethyl benzophenones.