Fries rearrangement of aryl esters catalysed by heteropoly acid: catalyst regeneration and reuse

Heteropoly acid H3PW12O40 (PW) supported on silica and its salt Cs2.5H0.5PW12O40 (CsPW), previously found as active solid acid catalysts in the liquid-phase Fries rearrangement of aryl esters, have been studied for the rearrangement of phenyl acetate and naphthyl acetate in a batch reactor. During the reaction even in nonpolar solvents such as dodecane, PW leached from the silica support. No leaching was found for CsPW in polar (nitrobenzene) or nonpolar (dodecane) solvents. Significant coking was observed for the high-porous PW/SiO2 (6-13 wt.% carbon), whereas the low-porous CsPW built only about 2 wt.% carbon. Both catalysts could be separated by filtration and, after a simple workup (washing with dichloroethane), reused, albeit with reduced activity. The reusability of CsPW improved when the workup included air calcination at 350degreesC, followed by steaming at 200degreesC. Doping CsPW with Pd (ca. 2%) allowed full regeneration of catalyst activity and selectivity in phenyl acetate (PhOAc) rearrangement by the air calcination and steaming. (C) 2003 Published by Elsevier B.V.