Single step synthesis of 4-hydroxybenzophenone via esterification and Fries rearrangement: Novelty of cesium substituted heteropoly acid supported on clay

Abstract

Hydroxybenzophenones are important precursors used in fine chemical and pharmaceutical industries. The esterification reaction of phenol with benzoic acid, followed by the Fries rearrangement towards hydroxybenzophenones in a one-pot liquid phase operation was examined with several catalysts under solvent-free conditions. Cesium substituted dodecatungstophosphoric acid supported on K-10 clay (designated as Cs_2.5H_0.5PW₁₂O₄₀/K-10) was found to be the most active and selective catalyst towards 4-hydroxybenzophenone in comparison with others. The order of activity was as follows: 20%w/wCs_2.5H_0.5PW₁₂O₄₀/K-10)(mostactive)∼(almostequal)UDTCaT-5>20%w/wCs_2.5H_0.5PW₁₂O₄₀/HMS>UDTCaT-6(least). The conversion of benzoic acid and selectivity for 4-hydroxybenzophenone at a phenol to benzoic acid mole ratio of 7:1, using 0.05 g/cm³ Cs_2.5H_0.5PW₁₂O₄₀/K-10 at 200 °C were 70% and 32.5%, respectively. The effects of various reaction parameters on the rate of reaction and selectivity were investigated.