α-1,3-Glucan benzoate – A novel polysaccharide derivative

Abstract

α-1,3-Glucan benzoates (GB) were prepared by homogeneous derivatization of the polysaccharide in N,N-dimethylacetamide (DMA)/LiCl using either benzoyl chloride as reagent (without and with addition of pyridine) or benzoic acid (using 1,1′-carbonyldiimidazole (CDI) for in situ activation of the carboxyl groups). A maximum degree of substitution (DS) of 1.96 was achieved by adjusting reaction time and molar ratio of reagent to anhydroglucose unit (AGU). The esterification with aromatic benzoate moieties was demonstrated by FTIR- and NMR spectroscopy. Substitution predominately occurred at the primary C-6 position with an order of reactivity of C6 » C2 > C4. The novel GB were soluble in dipolar aprotic solvents starting at DS ≥ 0.5 and melt at temperatures around 190 °C provided the DS is ≥ 1.7. Keywords: α-1,3-Glucan, Polysaccharide benzoates, Homogeneous derivatization, Esterification, NMR spectroscopy