Sustainable electrochemical depolymerization of chitosan into glucosamine hydrochloride using N-hydroxyphthalimide as a redox catalyst

Abstract

While chemical and enzymatic depolymerization of chitosan has been extensively studied, electrochemical methods achieving complete depolymerization into glucosamine (GlcN) building blocks have not been reported. Previous studies only reduced molecular weight without producing repeating unit sugars. Here, we demonstrate the direct electrochemical conversion of chitosan into glucosamine hydrochloride using N-hydroxyphthalimide (NHPI) as a green redox mediator under mild galvanostatic conditions. Conducted in acetate buffer with titanium mesh electrodes, the process affords crystalline GlcN in high yield. Structural analyses confirmed selective formation of both α- and β-anomers without detectable overoxidized by-products. Importantly, systematic kinetic studies of NHPI-mediated chitosan depolymerization, not previously reported, were performed. Electrochemical monitoring revealed a stable redox cycle between NHPI and its oxyl radical form, phthalimide-N-oxyl (PINO), along with progressive substrate consumption. This work establishes an operationally simple and environmentally benign electrochemical platform for selective building blocks production from polysaccharides, addressing an unmet need in chitosan valorization.