Chitosan supported ionic liquid, a multifaceted catalyst for streamlined and efficient synthesis of carboxylic, amino acid and carbohydrate esters

Abstract

This work presents a sustainable approach for synthesizing esters from carboxylic acids, amino acids and carbohydrates using a robust and eco-friendly chitosan-incorporated ionic liquid under solvent-free conditions. Ionic liquids with carbon chain lengths ranging from 3 to 8 were integrated into the chitosan molecule, resulting in a heterogeneous catalyst optimized for esterification reactions. Among these, the 6-carbon chain ionic liquid demonstrated superior catalytic activity and substrate tolerance. The catalyst's effectiveness was confirmed using advanced analytical techniques. The acidity of the ionic liquid was assessed by observing the interaction between the synthesized IL6 (1,4-bis(5-carboxypentyl)pyrazine-1,4-diium ([BCPPD][Br])) and p-nitroaniline via UV-Vis studies. Chitosan-IL6, an ionic liquid supported on chitosan, functions as a heterogeneous catalytic system that can be easily removed from reaction mixtures through simple filtration. It also exhibits excellent reusability, maintaining high catalytic activity and structural integrity over 10 catalytic cycles. Moreover, the methodology was successfully scaled up for the gram-scale synthesis of key compounds such as diisopropyl azodicarboxylate, methyl nicotinate, methyl cysteinate, and glucose pentaacetate, highlighting its practical viability.