Abstract
We report here the facile rare-earth triflate-catalyzed esterification of cellulose by carboxylic anhydrides, including acetic anhydride, at room temperature under solvent-free conditions. As a model, d-glucose was peraceylated using only equimolar amounts of acetic anhydrides against hydroxyl groups to give the expected 1,2,3,4,6-pentaacetyl α-d-glucopyranoside (crude yield 98%, 68% yield after recrystallization) under solvent-free condition. In the case of powdery microcrystalline cellulose, acetylation proceeded both in the absence of pyridine and solvent to give peracetylated cellulose, even in the bulk. From 1H NMR measurements, the degree of substitution (DS) was 3.0 (100% acetylation) and we concluded that Sc(OTf)3-catalyzed solvent-free esterification of cellulose had taken place. The number-average molecular weight (Mn), calculated using the 1H NMR intensity ratio based on the anomeric proton in the reducing terminus, was 1.7 × 104 (repeating unit of pyranose unit: 56).
Published Version
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