Anisole acylation silica-supported

Izumi et al. pioneered the use of heteropoly acids as catalysts for aromatic acylation. Silica-supported acids H4[SiWi204o] and H3[PWi204o] were found to effectively catalyse the acylation of p-xylene with benzoyl chloride. Cs2.5Ho.5[PWi204o] showed high efficiency in the acylation of activated arenes, such as p-xylene, anisole, mesitylene, etc., by acetic and benzoic anhydrides and acyl chlorides. This catalyst provided higher yields of acylated arenes than the parent acid H3[PWi204o], the latter being partly soluble in the reaction mixture. ... 

A detailed analytical study of fhe acfivity of some solid acid catalysts, including mesoporous silica-supported Nation, in the acylation of anisole with AAN allows the conclusion that catalyst deactivation is caused by the primary ketone product and/or multiple acetylated products in the micropores of Nation catalyst aggregates. i Experiments were performed with a commercially available silica-supported Nation catalyst in a continuous-mode slurry operation by using carbon-dioxide-expanded liquids (nitromethane or nitrobenzene) as solvents. At 90°C, 80% AAN conversion is observed with a TOS of 2 h, but the catalyst rapidly deactivates, and 27% conversion is evaluated after 6 h TOS with a TON value of about 400. The catalyst can, however, be completely regenerated upon nitric acid treatment. These results confirm that silica-supported Nation catalysts are promising alternatives for the traditional aluminum chloride homogeneous Lewis acid catalyst. 

H. M. C. 2004. Friedel-Crafts acylation of anisole with acetic anhydride over silica-supported heteropolyphosphotungstic acid (HPW/SiOj). /. Mol. Catal. A Chem. 209 189-197. 

Our recent study ° showed that bulk and silica-supported H3[PWi204o] exhibit a very high activity in the acylation of anisole (Eq. 4) with acetic anhydride in liquid phase, yielding up to 98% para and 2 - 4% ortho isomer of methoxyacetophenone (MOAP) at 70 - 110"C and an anisole to acetic anhydride molar ratio AN/AA = 10-20 (Table 1). 

Gallium(lll) oxide supported on MCM-41 mesoporous silica shows high catalytic activity with little or no moisture sensitivity in the acylation of aromatics wifh acyl chlorides. The cafalysf is utilized in 1,2-dichloro-ethane af 80°C for 3 h wifh differenf aromatic compounds, and aromatic as well as aliphatic acyl chlorides, giving ketones in 54%-82% yield. The activity order of fhe aromatic subsfrafes is benzene (43% yield) < toluene (50% yield) < mesifylene (71% yield) < anisole (79% yield), in agreement with the electrophilic substitution trend previously observed. This acylation reaction follows a probable redox mechanism similar to thaf described in Scheme 4.26. ... 

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