The transformations involving methanol in the acid- and base-catalyzed gas-phase methylation of phenol

The alkylation of phenol with methanol was studied using a Bronsted-type acid catalyst (a H-mordenite) and basic/dehydrogenating catalysts (MgO, Fe2O3 and Mg/Fe/O), with the aim of investigating the reaction mechanism. The main difference between the two classes of catalysts concerned the transformations occurring on methanol. Specifically, in the former case the acid-type activation of methanol led to the development of an electrophylic species that gave rise to the formation of anisole and of C-alkylated compounds. With basic catalysts, methanol dehydrogenated to formaldehyde, which then underwent transformation to methylformate and to decomposition products, i.e., CO, CO2, CH4 and H-2. In this case, the prevailing compounds obtained by reaction with phenol were o-cresol and 2,6-xylenol. The dehydrogenation of methanol was found to be the key-step in the generation of the active methylating species with basic catalysts. (C) 2001 Elsevier Inc. All rights reserved.