Synthesis and characterization of branched polysaccharides by reaction of cellulose with 2,3,4,6-tetraacetyl-1-bromo-α-D- glucopyranoside

Non-naturally branched polysaccharides were prepared homogeneously by reaction of cellulose in N,N-dimethyl acetamide/LiCl and the ionic liquid 1-N-butyl-3-methylimidazolium chloride with 2,3,4,6-tetraacetyl-1-bromo-α-D-glucopyranoside in the presence of triethylamine as base. Degrees of substitution up to 0.58 were realized. The samples were soluble in dimethyl sulphoxide and water. NMR spectroscopy and methylation analysis revealed the formation of 1,2-orthoesters. The purity of the products regarding non-bonded sugar molecules was evidenced by advanced NMR techniques (DOSYand T2 measurements). In contrast to the reaction in 1-N-butyl-3-methylimidazolium chloride, 1-N-ethyl-3methylimidazolium acetate acts not only as solvent but also as reagent and leads to the formation of cellulose acetate instead of the desired product.