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

A series of insoluble cesium partly substituted Wells–Dawson type heteropolyacids, CsxH6−xP2W18O62 (x = 1.5–6.0), were synthesized and characterized using the techniques including UV–vis/DRS, FT-IR, XRD, XPS, and N2 porosimetry. As the unique and reusable solid acid catalysts, CsxH6−xP2W18O62 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 (CsxH3−xPW12O40, 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 Cs1.5H4.5P2W18O62 and Cs2.5H0.5PW12O40 exhibited excellent catalytic performance under solvent-free conditions. Furthermore, both selectivity and activity of Cs1.5H4.5P2W18O62 were higher than those of Cs2.5H0.5PW12O40. Reasons for the different catalytic behaviors between two types of cesium partly substituted heteropolyacids were investigated.

Graphical abstractA series of insoluble cesium partly substituted Wells–Dawson-type heteropolyacid, CsxH6−xP2W18O62 (x = 1.5–6.0), are synthesized. As the unique and reusable solid acid catalysts, CsxH6−xP2W18O62 have good catalytic performance for the condensation reaction of phenol with bio-platform molecule, levulinic acid, to produce diphenolic acid under solvent-free condition.Figure optionsDownload full-size imageDownload as PowerPoint slide