Propionylation of phenol to 4-hydroxypropiophenone over zeolite H-beta

The liquid phase propionylation of phenol (Ph) with propionyl chloride (PC) has been studied over zeolite H-beta, Re-Y, H-Y, mordenite, H-ZSM-5 and AI Cl(3) at 413 K. H-beta catalyzes the reaction to 4-hydroxypropiophenone (4- HPP), 2-hydroxypropiophenone (2-HPP) and phenylpropionate (PP) as major pro ducts. H-beta is found to be superior to other zeolite catalysts and AlCl3. The product distribution largely depends upon the reaction conditions and acidity of the zeolite catalysts. The acidity of the zeolite catalysts was measured by the temperature programmed desorption of ammonia. The conversio n of phenol remains nearly constant due to the rapid formation of PP. The y ield of the 2-HPP and 4-HPP increases with the increase in reaction time, H -beta to Ph (w/w) ratio, reaction temperature and phenol:PC molar ratio. Th e H-beta was recycled two times and a decrease in the yield of 2-HPP and 4- HPP was observed after each recycle. Plausible reaction pathways are propos ed for the formation of PP, 2-HPP, 4-HPP and 4-propionyloxypropiophenone (4 -PXPP) using zeolite as catalyst. Mostly, the reaction pathways are found t o be similar to that of acetylation of phenol. The O-propionylation of phen ol is much faster than the C-propionylation. The PP results from the rapid O-propionylation of phenol with PC. 2-HPP is produced through the Fries rea rrangement of PP, propionylation of phenol with PP and direct C-propionylat ion of phenol with PC. 4-HPP is produced by the reaction of 4-PXPP with zeo lite hydroxyl groups, small amount of 4-HPP is also produced through the di rect propionylation phenol with PC and propionylation of phenol with PP, wh ereas formation of 4-PXPP takes place by the bimolecular reaction of two PP molecules. (C) 2001 Elsevier Science B.V. All lights reserved.