Novel aluminium exchanged dodecatungstophosphoric acid supported on K-10 clay as catalyst: benzoylation of diphenyloxide with benzoic anhydride

Abstract

A series of (20% w/w) aluminium exchanged dodeca-tungstophosphoric acids (DTP) (Al_x-DTP, x = 0.33–1) supported on montmorillonite K-10 clay were synthesized and completely characterized by sophisticated techniques. These catalysts were used for the selective benzoylation of diphenyl oxide with benzoic anhydride to a mono acylated product. Al_0.66-DTP/K-10 catalyst showed the best activity amongst other aluminium substituted catalysts and Cs_2.5H_0.5PW₁₂O₄₀ (Cs-DTP)/K-10. Different supports such as ZrO₂, SnO₂ and K-10 were used to study the effect of support on the acidic property and activity of Al_0.66-DTP supported catalysts in the benzoylation reaction. The order of activity was Al_0.66-DTP/K-10 > Al_0.66-DTP/SnO₂ > Al_0.66-DTP/ZrO₂. The effect of benzoylating agents such as benzoic anhydride, benzoyl chloride and benzoic acid on the conversion and rate was also studied. Benzoic anhydride showed the highest reactivity. Eley–Rideal mechanism was found to be consistent with the data. The activation energy for benzoylation of DPO was calculated as 22 kcal mol⁻¹, which further supports that the reaction is kinetically controlled. Al_0.66-DTP/K-10 was an active and robust catalyst.