On the mechanism of the unwanted acetylation of polysaccharides by 1,3-dialkylimidazolium acetate ionic liquids: part 1—analysis, acetylating agent, influence of water, and mechanistic considerations

Abstract

The acetylating action of ionic liquids frequently used in biomass and polysaccharide processing, namely 1,3-dialkylimidazolium acetates, on cellulose has been studied. Analysis was based on an accurate method to quantify even minute amounts of organic acetates in polysaccharides. The acetylation is caused by impurities in the ionic liquids, specially purified ionic liquids do not show an acetylating effect. 1-Acetylimidazole has been proven to be the actual acetylating agent, and its presence in aged ionic liquids has been confirmed. Formation of the reagent, mechanism of its action—being an acetyl transfer rather than a typical esterification—kinetics of the acetylation and the effect of water in the system are studied in detail. The implications on processing of biomaterials in ionic liquids are discussed as well.