Sulfonated Porous Aromatic Frameworks as Solid Acid Catalysts

The synthesis, characterization, sulfonation, and catalytic performance of two new porous aromatic frameworks are presented. The polymers, which were obtained by the Suzuki-Miyaura cross-coupling of the commercially available precursors 1,3,5-tris(4-bromophenyl)benzene or tris(4-bromophenyl)amine and benzene-1 4-diboronic acid, only contain aromatic sp² C-C and C-N bonds, display excellent thermal and chemical stability, and allow for post-synthetic functionalization under very harsh reaction conditions. Upon post-synthetic treatment at 160 °C in 98 wt % sulfuric acid, approximately 65 % of the benzene rings in the polymers were sulfonated. The materials were characterized by solid-state NMR spectroscopy, X-ray photoelectron spectroscopy, FTIR spectroscopy, and textural analysis. The sulfonated materials display an excellent catalytic performance in the acid-catalyzed esterification of n-butanol and acetic acid and have a similar or even superior performance to that of state-of-the-art Amberlyst-15 over multiple catalytic cycles. Making the frame work: Sulfonated porous aromatic frameworks synthesized by Suzuki-Miyaura cross-coupling display an excellent catalytic performance in the acid-catalyzed esterification of n-butanol and acetic acid with a similar or superior performance to state-of-the-art Amberlyst-15 over multiple catalytic cycles.