Gas phase acylation of guaiacol with acetic acid on acid catalysts

[Display omitted] •Product distribution considerably changes with the acid catalyst nature.•O-acylation reaction is favored on Brønsted acid sites (HPA/SiO2).•HZSM-5 and ZnZSM-5 display the highest C-acylation/O-acylation ratio.•Catechol formation by demethylation competes with acylation. Gas phase acylation of guaiacol on acid solids was studied using catalysts with different acid site density, nature and strength. The main products formed were acetovanillone, 2-acetoxyanisole and catechol using acetic acid as acylating reactant. The product distribution considerably changed with the catalyst nature. Catalysts with Lewis and Brønsted acid sites promoted both the O-acylation route (2-acetoxyanisole formation) and C-acylation route (acetovanillone formation) and formed catechol mainly by demethylation of guaiacol; catalysts with large pore size also favored catechol formation by a bimolecular disproportionation reaction. Catalyst deactivation took place, thus the coke formation was studied suggesting that the Lewis acid sites, responsible of catechol formation, were more affected by deactivation. The effect of reaction temperature, molar reactant ratio and the use of different acylating molecules on guaiacol conversion and products formation were also evaluated. HZSM-5 catalyst, 523 K and acetic acid were appropriate to promote C-acylation during gas phase guaiacol acylation.