Formation of Hexamethylbenzene from Phenol and Methanol

Abstract

In the reaction of phenol with methanol over an active alumina catalyst to form hexamethylbenzene, it was found that pentamethylbenzene, tetramethylbenzenes, trimethylbenzenes, polymethylphenols and methylethers of polymethylphenols were also produced. Main by-products were pentamethylbenzene, 1, 2, 3, 5-tetramethylbenzene, 1, 2, 4-, 1, 3, 5-trimethylbenzene, 2, 3, 6-, 2, 4, 6-trimethylphenol, 2, 3, 4, 6-tetramethylphenol and pentamethylphenol. The amounts of these by-products increased with decrease in the amount of methanol in the starting materials and with lowering of the reaction temperature. Furthermore, pentamethylbenzene and tetramethylbenzene were readily converted to hexamethylbenzene under the reaction conditions, exclusively without formation of tetra- and tri-methylbenzenes. Tetra- and tri-methylbenzenes were probably converted from tetra- and tri-methylphenols, respectively, but the amounts of these methylbenzenes were smaller than pentamethylbenzene in the reaction products.
A plausible main reaction path for the conversion of phenol to hexamethylbenzene is the following: phenol 2, 6-xylenol. 2, 4, 6- and 2, 3, 6-trimethylphenol - 2, 3, 4, 6-tetramethylphenol pentamethylphenel pentamethylbenzene hexamethylbenzene.