Catalytic synthesis of diphenolic acid from levulinic acid over cesium partly substituted Wells–Dawson type heteropolyacid

Abstract

A series of insoluble cesium partly substituted Wells–Dawson type heteropolyacids, Cs x H 6− x P 2W 18O 62 ( x = 1.5–6.0), were synthesized and characterized using the techniques including UV–vis/DRS, FT-IR, XRD, XPS, and N 2 porosimetry. As the unique and reusable solid acid catalysts, Cs x H 6− x P 2W 18O 62 salts were applied to produce diphenolic acid by the condensation reaction of phenol with bio-platform molecule, levulinic acid. For comparison, cesium partly substituted Keggin type heteropolyacids (Cs x H 3− x PW 12O 40, x = 1.0–3.0), HCl, HZSM-5, and MCM-49 were also tested. Influences on the catalytic activity and selectivity were considered for factors including solvent, molar ratio of phenol to levulinic acid, amount of catalyst, reaction temperature, stirring speed, and reaction time. The experimental results demonstrated that both Cs 1.5H 4.5P 2W 18O 62 and Cs 2.5H 0.5PW 12O 40 exhibited excellent catalytic performance under solvent-free conditions. Furthermore, both selectivity and activity of Cs 1.5H 4.5P 2W 18O 62 were higher than those of Cs 2.5H 0.5PW 12O 40. Reasons for the different catalytic behaviors between two types of cesium partly substituted heteropolyacids were investigated.