Friedel–Crafts acylation of anisole with octanoic acid over acid modified zeolites

Abstract

Friedel–Crafts acylation of anisole using octanoic acid as a green acylating agent was studied over zeolites free of solvent. It was found that a mixed organic acid, composed of tartaric acid and oxalic acid, modified Hβ (Mix-Hβ) zeolite showed the best catalytic performance among the catalysts studied. The conversion of octanoic acid and the selectivity for p-octanoyl anisole were 72.7% and 82.5%, respectively. Inductively coupled plasma analysis (ICP) and ²⁷Al MAS NMR indicated dealumination of the parent Hβ zeolite due to the treatment of the mixed organic acid, leading to more accessible active sites and accounting for the better catalytic activity of the Mix-Hβ zeolite. Furthermore, lower strength of Lewis acid sites and Brönsted acid sites of the Mix-Hβ zeolite, as demonstrated by Fourier Transform Infrared Spectrometry after adsorption of pyridine (Py-IR), are advantageous to suppress the demethylation of anisole and the subsequent esterification of thus formed phenol, accounting for its higher selectivity toward p-octanoyl anisole.