Catalytic Conversion of Chitosan to Glucosaminic Acid by Tandem Hydrolysis and Oxidation

Effective conversion of chitin or its derivatives (i.e., chitosan) to value-added organonitrogen compounds is a promising strategy to valorize chitin. Glucosaminic acid (GlcNA) is an important amino acid derived from chitosan. In this work, we demonstrate the feasibility of GlcNA production from chitosan by tandem hydrolysis and oxidation reactions without isolating glucosamine (GlcN) intermediate. The Amberlyst-15 and Au/MgO were identified as suitable catalysts for the hydrolysis and oxidation step, respectively, but the direct employment of hydrolysate from the first step in further oxidation resulted in very low yield of target amino acid. We show that humin-like polymers formed during hydrolysis poisoned Au/MgO, resulting in low GlcNA yield, and subsequently a key detoxication process of the hydrolyzed mixture using activated carbon was developed. It effectively removed the undesired side products that inhibit Au catalyzed oxidation reaction, markedly enhancing the GlcNA yield from 17% for untreated hydrolysate to 63% for preadsorbed sample. As such, a two-step process is developed to produce GlcNA from chitosan with an overall yield of 36%.