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, Cs(x)H(6-x)P(2)W(18)O(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(2)W(18)O(62) salts were applied to produce cliphenolic 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(12)O(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(1.5)H(4.5)P(2)W(18)O(62) and Cs(2.5)H(0.5)PW(12)O(40)) exhibited excellent catalytic performance under solvent-free conditions. Furthermore, both selectivity and activity Of Cs(1.5)H(4.5)P(2)W(18)O(62) were higher than those of Cs(2.5)H(0.5)PW(12)O(40). Reasons for the different catalytic behaviors between two types of cesium partly substituted heteropolyacids were investigated. (C) 2008 Elsevier B.V. All rights reserved.