DIRECT FRIES REACTION OF RESORCINOL WITH BENZOIC-ACIDS CATALYZED BY ZEOLITE H-BETA

The esterification reaction of resorcinol with benzoic acid, followed by the Fries rearrangement towards benzophenones in a one-pot liquid phase operation was examined with several catalysts. Zeolite H-beta and ion-exchange resins (Amberlyst-15, Nafion-117) were found to be the best catalysts for both equilibrium reactions. More insight in the Fries rearrangement was obtained by carrying out the reaction with a series of substituted phenols and substituted benzoic acids, especially with zeolite H-beta as the catalyst. The esterification reaction of resorcinol with hindered benzoic acids (2-Me- and 2,6-diMe-benzoic acid) is relatively rapid and an intermediate acylium ion is suggested. Here the rate of the rearrangement to the benzophenones is catalyst dependent; with zeolite H-beta the rearrangement of resorcinol-2-Me-benzoate is fast (yield > 90%) and the rearrangement of resorcinol-2,6-diMe-benzoate is slow because of the pore dimensions of the zeolite (shape effect). With Amberlyst-15 as the catalyst both rearrangements are fast. n-Butylbenzene, p-Cl-toluene and n-decane are found to be good solvents in this one-pot reaction. The industrial chemical 2,4-dihydroxybenzophenone can be prepared in a 88% yield by a recycling procedure starting from benzoic acid and resorcinol with zeolite H-beta as the catalyst and with n-butylbenzene as the solvent. In contrast to the existing process the present approach is a clean method.