Continuous synthesis of bis(indolyl)phenylmethane over acid modified Hβ zeolite

The continuous synthesis of bis(indolyl)phenylmethane has been successfully accomplished for the first time by Friedel-Crafts alkylation of indole with benzaldehyde in a fixed-bed reactor over different zeolites. A citric acid modified Hβ (CA-Hβ) zeolite showed better catalytic performance than parent Hβ zeolite due to its larger surface area and smaller amount of weak acid sites, confirmed by the Brunauer–Emmett–Teller (BET) method, NH3 temperature-programmed desorption (NH3-TPD) and Fourier Transform Infrared Spectrometer after adsorption of pyridine (Py-IR). Furthermore, it is proposed that citric acid treatment is appropriate for dealumination of Hβ zeolite, which results in the CA-Hβ zeolite having a larger number of active centers for the desired transformation. Significantly, CA-Hβ has shown good stability during a 100 h test.

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► Modified Hβ zeolite was used for synthesis of bis(indolyl)phenylmethane (BIPM).
► A continuous process for synthesis of BIPM over zeolites was first established.
► A citric acid modified Hβ zeolite has shown good activity and excellent stability.
► Dealumination and weak acid sites were proven to favor the desired transformation.