Microwave-assisted Friedel–Crafts acylation of indole with acetic anhydride over tungstophosphoric acid modified Hβ zeolite

Friedel–Crafts acylation of indole with acetic anhydride has been carried out over zeolites under microwave and conventional heating, respectively. A tungstophosphoric acid modified Hβ (PW-Hβ) zeolite showed better catalytic performance than parent Hβ zeolite due to its higher amount of strongly acidic sites and lower amount of Lewis acid sites, confirmed from NH3 temperature-programmed desorption (NH3-TPD) and Fourier Transform Infrared Spectrometer after adsorption of pyridine (Py-IR). Particularly, microwave radiation was found to make this transformation not only more efficient but also selective to 3-acetylindole compared with conventional heating. Furthermore, PW-Hβ has shown good stability in this reaction.

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► Friedel–Crafts acylation of indole with acetic anhydride was studied over zeolites.
► Microwave was believed to make this transformation more efficient and selective.
► Tungstophosphoric acid modified Hβ was proven to have good activity and stability.
► Synergistic effect of Hβ zeolite and WO3 accounts for the catalyst's high activity.
► A possible mechanism was proposed based on GC-MS results and previous literature.