Metal-free mesoporous carbon nitride catalyze the Friedel–Crafts reaction by activation of benzene

Abstract

Mesoporous graphitic carbon nitride (mpg-C₃N₄) was synthesized and studied as a metal-free catalyst for Friedel–Crafts acylation of benzene. The synthesis was done by a template method using SiO₂ as template and organic chemicals including guanidine hydrochloride (GndCl), dicyandiamide and urea as precursors. Characterizations by XRD, FT-IR, XPS, N₂ physisorption and TEM indicated that the assumed mpg-C₃N₄ is synthesized irrespective of the precursor used. However, the surface chemistry of mpg-C₃N₄, evaluated from TGA and CO₂-TPD, varied with the precursors and the mass ratio (r) of SiO₂ to precursor. Catalytic results showed that the sample prepared using GndCl as precursor and at mass ratio of SiO₂ to GndCl equals to 0.7, defined as mpg-C₃N₄_G_(0.7), exhibits the best activity for the reactions, due to its rich surface basic sites and high surface area. Thus 89% conversion was obtained within 30 min using hexanoyl chloride as electrophile at 90 °C. Even at room temperature (27 °C), 75% conversion can be observed within 30 min. The catalyst is also reusable with ca. 80% activities recoverable after washing with ethanol. The excellent catalytic performances, as well as its low cost, straightforward synthesis and metal-free characters, make mpg-C₃N₄_G_(0.7) a potential catalyst for Friedel–Crafts acylation of benzene in industry with a “green” route.