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