Ortho-selective alkylation of phenol with 1-propanol catalyzed by CeO2-MgO

Vapor-phase alkylation of phenol with l-propanol was investigated over CeO(2M)gO catalysts prepared utilizing a molten mixture of the corresponding nitrates and citric acid. The CeO2-MgO had a stable catalytic activity at 475 degrees C, and had an excellent selectivity to 2-propylphenol, higher than 82% based on phenol. Although a portion of the 2-propylphenol produced was decomposed into o-cresol and 2-ethylphenol, a sum of selectivities to the monoalkylated phenols exceeded 97%. During the alkylation, propanal and 3-pentanone was observed. In the results of l-propanol conversion without phenol, it was found that l-propanol was dehydrogenated to propanal and that the propanal produced was dimerized to 3-hydroxy-2-methylpentanal via aldol addition, followed by the deformylation into 3-pentanone. Namely, in the reaction of phenol and 1-propanol, the propylation of phenol and the dehydrogenation of 1-propanol occurred concurrently over the CeO2-MgO. The pure CeO2, having both the redox property with Ce4+-Ce3+ and weak basic sites, catalyzed both the propylation of phenol and the 1-propanol transformation into 3-pentanone, while the pure MgO with strong basicity was less active for the 1-propanol transformation and had a low reaction rate in the alkylation. The reaction mechanism of the ortho-propylation over the CeO2-MgO catalyst is speculated as follows. The ortho position of phenol adsorbed perpendicularly on weak basic sites of the catalyst is selectively alkylated by 1-propanol, which is possibly activated in the form of 1-hydroxypropyl radical on CeO2 species rather than as a form of n-propyl cation. The redox property of CeO2 is probably attributed to the homolitic activation of 1-propanol to produce 1-hydroxypropyl radical. (C) 1999 Academic Press.