Efficient fatty acid esterification using silica supported Brønsted acidic ionic liquid catalyst: Experimental study and DFT modeling

• A heterogeneous Brønsted acid catalyst for efficient fatty acid esterification.
• It comprises a [BnMIm]HSO4 ionic liquid confined onto the mesoporous silica gel.
• The activity of the supported ionic liquid is superior to homogeneous system.
• DFT simulation was performed for the catalyst.
• The efficiency of the catalyst is attributed to the value of ΔHacidity and hydrophobic effect.

A task-specific Brønsted acidic ionic liquid (BAIL), 1-benzyl-3-methylimidazolium hydrogensulfate ([BnMIm]HSO4), was prepared and confined onto the high surface area silica gel. The catalyst has shown extraordinary activity in comparison of homogeneous ionic liquid (IL) system for Fischer esterification of fatty acid with ethanol. The ester derivatives were synthesized in high yields and catalyst was easily separated from the reaction mixture by simple filtration. The structure of the catalyst is theoretically modelized to investigate the unusual catalytic activity. Hence, a hydroxylated cage-like nano-cluster, H6Si8O12(OH)2, was selected to mimic the surface of silica gel. The interactions between the IL and this cluster have been studied using density functional theory (DFT) calculations. DFT modeling indicates that the acidity of the supported [BnMIm]HSO4 is higher than the homogeneous BAIL system.

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