Selective benzoylation of naphthalene to 2-benzoylnaphthalene using zeolite H-beta catalysts

The liquid phase benzoylation of naphthalene over various zeolites has been investigated in the temperature range 333-358 K using benzoyl chloride (BOC) as the benzoylating agent. H-beta catalyzes the reaction efficiently and selectively to 2-benzoylnaphthalene (2-BON) and is found to be superior to the other zeolite catalysts and AlCl3. The conversion of benzoyl chloride to the products largely depends upon the reaction conditions and acidity of the zeolite catalysts. The acidity of the zeolite was measured by temperature programmed desorption of ammonia. It was observed that the conversion of BOC increased with the increase in time on stream, catalyst to BOC (wt./wt.) ratio, naphthalene to BOC molar ratio and reaction temperature. Under the reaction conditions (1 atm, 358 K, H-beta to BOC (wt./wt.) = 0.37, naphthalene to BOC (molar ratio) = 2. 17.6 wt.-% conversion of BOC and a selectivity for 2-BON of 74.8 wt.-% were obtained. Benzoic anhydride and benzoic acid were also used in the reaction. The catalyst, H-beta, was recycled four times and a slight decrease in BOC conversion was observed after each cycle which was related to the minor dealumination of zeolite catalyst by HCl (formed during reaction). The formation of benzoylnaphthalenes is explained by an electrophilic attack of the benzoyl cation (C6H5CO+) on the naphthalene ring whose formation is facilitated by the stronger acid sites of the zeolite catalysts.