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

Abstract The alkylation of phenol with methanol was studied using a Bronsted-type acid catalyst (a H-mordenite) and basic/dehydrogenating catalysts (MgO, Fe 2 O 3 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, CO 2 , CH 4 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.