Vilcocq Castilho*, Zatta Ramos, Murillo Bruijninc, Nowakowska Bogdan

ABSTRACT

: Novel allylimidazolium-based ionic liquids (ILs) with Brønsted acid functionalities, bearing triflate ([ASBI][TfO]) and sulfate ([ASBI][HSO?]) anions, along with their Lewis acid derivatives ([ASCBI][TfO] and [ASCBI][HSO?]), were synthesized and covalently immobilized on silica via a thiol (-SH) anchoring group. Comprehensive characterization—including FTIR, thermogravimetric analysis (TGA), elemental composition, N? adsorption, and acidity measurements—confirmed successful immobilization and high surface acidity. These hybrid materials acted as efficient Brønsted and Lewis acid catalysts in the esterification of glycerol (C?H?O?) with acetic acid (CH?COOH), exhibiting superior selectivity toward diacetin (DAG) and triacetin (TAG) compared with conventional heterogeneous acid catalysts. Low-conversion studies were used to distinguish between 1,3- and 1,2-diacetin formation. Investigations with diols of varying chain lengths demonstrated that diacetin selectivity is strongly influenced by substrate structure. Among the catalysts, SiO?-[ASBI][HSO?] exhibited the highest activity and was further studied to evaluate the influence of reaction time, temperature, catalyst loading, and glycerol to-acetic acid molar ratio on product distribution. The immobilized ionic liquids showed excellent recyclability, thermal stability, and catalytic efficiency, indicating their potential for sustainable glycerol valorization. Keywords: Allylimidazolium ionic liquids; SiO?-supported catalysts; Glycerol esterification; Diacetin; triacetin; Bronsted acidity; Lewis acidity.