Sulfated Ce xZr 1− xO 2 solid acid catalyst for solvent free synthesis of coumarins

Abstract

A novel SO 4 2−/Ce x Zr 1− x O 2 catalyst has been employed for Pechmann condensation of phenols under solvent-free conditions. Catalyst loads as low as 10 wt.% could be used leading to high yields with activated phenols at an oil bath temperature of 393 K. To make the catalyst, Ce–Zr–hydroxide gel was prepared by a coprecipitation method and SO 4 2− ions were deposited by treating the gel with sulfuric acid and calcined at 923 K. Surface and bulk properties of the catalyst was investigated by means of X-ray powder diffraction, ammonia-temperature programmed desorption, Raman spectroscopy, and BET surface area methods. Characterization results reveal the super acidic nature of the catalyst. The methodology presented offers significant improvements for the synthesis of coumarins with regard to yield of products, simplicity in operation, and green aspects by avoiding toxic conventional catalysts and solvents.