Fast and highly efficient acetylation of xylans in ionic liquid systems

In this study high molecular weight pure rye arabinoxylan and spruce arabinoglucuronoxylan were acetylated in ionic liquid (IL) systems. Two different ILs were used in our study. In both IL, using optimized procedures, it was possible to achieve acetylation within 5 min. The first system involved direct dissolution into 1-ethyl-3-methylimidazolium dimethylphosphate ([emim][Me₂PO₄]), followed by addition of acetyl chloride/pyridine (AcCl/Pyr) and additional chloroform (CHCl₃), as co-solvent. The other system involved direct dissolution into the novel protic IL 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]), followed by acetic anhydride/1,5-diazabicyclo[4.3.0]non-5-ene (Ac₂O/DBN) and no co-solvent added. The full acetyl substitution of the xylans was confirmed by FT IR and ¹H NMR. The acetylated xylans maintained a high molecular weight, which was confirmed by gel permeation chromatography. The products were soluble in CHCl₃ and dimethyl carbonate, which is considered as a 'green' reagent or solvent. This allowed for the casting of the materials into clear transparent films, opening opportunity for further processing and evaluation of these materials.