Catalysis of Organic..

Ardizzi et al. 85the selectivity to phenylbenzoate rapidly declined, in favor of the formation of theortho and para isomers of hydroxybenzophenone and of benzoylphenylbenzoate.10080phenylbenzoateSelectivity, %6040o- and p-benzoylphenylbenzoate200o-hydroxybenzophenonep-hydroxybenzofenone10 20 30 40 50 60 70Phenol conversion, %Figure 2. Selectivity to products as functions of phenol conversion. Catalyst H-β150. T 200°C.The data clearly indicate that the only primary product was phenylbenzoate,while all the other compounds formed by consecutive reactions upon the ester.Therefore, the scheme of reaction is that one summarized in Figure 3. The formationof the ester as the only primary product represents one important difference withrespect to the Friedel-Crafts benzoylation of phenol with benzoylchloride orbenzyltrichloride, catalyzed by AlCl 3 . In the latter case, in fact, the product of para-C-acylation (p-hydroxybenzophenone) is the main product of reaction; this is due tothe fact that AlCl 3 coordinates with the O atom of the hydroxy group in phenol, andmakes it less available for the ester formation, due to both electronic and stericreasons.OOHO H+O O H OOOOO+ H 2 OOO+ phenolFigure 3. Reaction scheme for the reaction between phenol and benzoic acidcatalyzed by the H-β zeolite.