Friedel–Crafts acylation of anisole over Cr-doped Hβ zeolite

Abstract

Cr-doped Hb zeolite is found to have better catalytic performance than Hb zeolite in the Friedel-Crafts acylation of anisole, with acetic anhydride conversion of over 99% and nearly 100% selectivity to furnish para-methoxyacetophenone under the optimized reaction conditions. This is attributed to the increase of weak and moderately strong acid sites, caused by the Cr addition. The formation of carbonaceous materials and their coating of the acid sites are believed to be the reasons for the deactivation of the reused Cr-doped Hb zeolite, as indicated by the Brunauer-Emmett-Teller (BET) method, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and NH 3 temperature-programmed desorption (NH 3 -TPD) measurement results. The catalyst activity can be recovered by a subsequent calcination.

Determination of different acid sites in Beta zeolite for anisole acylation with acetic anhydride

“…Friedel-Crafts acylation of aromatics is one of the most important synthetic reactions in manufacturing aromatic ketones, which are the key intermediates in fine chemicals, agrochemicals, pharmaceuticals, and fragrance industrial processes [1][2][3]. The conventional method of preparing aromatic ketones is acylation of aromatics with an acylation reagent, such as acid halides and anhydrides, and in the presence of Lewis acids (e.g., AlCl 3 ) or strong protonic acids (e.g., HF) [4,5].…”

“…The conventional method of preparing aromatic ketones is acylation of aromatics with an acylation reagent, such as acid halides and anhydrides, and in the presence of Lewis acids (e.g., AlCl 3 ) or strong protonic acids (e.g., HF) [4,5]. However, these traditional catalysts have some limitations, such as environmental pollution arising from the disposal of spent catalysts and toxic wastes, reactor corrosion, and product isolation [2,3,6,7]. Moreover, more stoichiometric quantity of catalyst is required, as the metal halide itself has a tendency of complexation with the ketone product [1,3,5].…”

“…However, these traditional catalysts have some limitations, such as environmental pollution arising from the disposal of spent catalysts and toxic wastes, reactor corrosion, and product isolation [2,3,6,7]. Moreover, more stoichiometric quantity of catalyst is required, as the metal halide itself has a tendency of complexation with the ketone product [1,3,5]. In order to overcome these drawbacks, considerable efforts have been made to explore heterogeneous solid acid catalysts, including solid superacid, heteropolyacid, and zeolite [8][9][10].…”

“…For example, Corma et al [14] showed that the catalytic activity of HY zeolite in the acylation of AN with phenylacetyl chloride was independent of their acid strength, indicating that all the weak, medium, and strong acid sites were active in this reaction. On the other hand, only weak and moderate acid sites were found to play an important role in the acylation of AN with acetic anhydride (AA) over Cr-doped Beta zeolite [3]. In addition, many researchers suggested that Brönsted acid sites were responsible for Friedel-Crafts acylation [1,[15][16][17][18].…”

“…In this work, the catalytic performances over Beta (Si/Al 2 of 64) samples with different acidities for the acylation of AN with AA have been evaluated in order to shed light on the catalytic roles of different acid sites in Beta zeolite. 3 solution with different concentrations in vacuum and followed by drying at 80°C and calcining at 530°C for 2 h. Here, x means the nominal amount of potassium loaded on 100 g Beta zeolite.…”