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

Abstract

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 AlCl3 at 413 K. H-beta catalyzes the reaction to 4-hydroxypropiophenone (4-HPP), 2-hydroxypropiophenone (2-HPP) and phenylpropionate (PP) as major products. 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 conversion of phenol remains nearly constant due to the rapid formation of PP. The yield 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. The 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 proposed for the formation of PP, 2-HPP, 4-HPP and 4-propionyloxypropiophenone (4-PXPP) using zeolite as catalyst. Mostly, the reaction pathways are found to be similar to that of acetylation of phenol. The O-propionylation of phenol 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 rearrangement of PP, propionylation of phenol with PP and direct C-propionylation of phenol with PC. 4-HPP is produced by the reaction of 4-PXPP with zeolite hydroxyl groups, small amount of 4-HPP is also produced through the direct propionylation phenol with PC and propionylation of phenol with PP, whereas formation of 4-PXPP takes place by the bimolecular reaction of two PP molecules.