Quantitative functionalization of chitosan using green and efficient azetidinium-amine reactions

Abstract

Despite significant advances in the field, quantitative post-polymer modification of chitosan, specifically attaching diverse hydrophobic moieties with experimentally predefined (via the ratio of reagents) degree of functionalization remain extremely challenging. In this context, we report our studies towards the use of green and efficient azetidinium-amine reactions to prepare a library of modified chitosan with a predefined degree of functionalization, with excellent conversion (>90%), atom economy and very low E-factor (<0.1). Initially six different azetidinium functionalized coupler molecules, which contains azetidinium functionality attached with other defined target functionality (ranging from hydrophobic to hydrophilic) are synthesized. In the next stage the azetidinium functionalized coupler molecules are reacted with chitosan (both low molecular weight and high molecular weight chitosans are used) in presence of 1,4-diazabicyclo[2.2.2]octane(DABCO, as base) using water as solvent and the other functional moiety are attached with the chitosan backbones. The degree of functionalization was calculated using ¹H NMR and excellent match (80-100%) was noted between calculated degree of functionalization and feed ratio of the reagents used (experimentally defined ratio).

Keywords: Azetidinium-amine reactions; Chitosan derivatives; Post-polymer modifications; Synthesis of azetidinium compounds.