C2-Functionalized 1,3-dialkylimidazolium ionic liquids for efficient cellulose dissolution

Abstract

Novel C2-functionalized 1,3-dialkylimidazolium-based ionic liquids (ILs) are prepared, in which the acidic hydrogen at the 2-position of 1,3-dialkylimidazolium is replaced with the oxygen-containing methoxymethyl (CH3OCH2-, MOM) and (2-methoxyethoxy)methyl (CH3OCH2CH2OCH2-, MEM) groups to increase their hydrogen bonding interactions with cellulose. While the chloride salts of these C2-functionalized imidazolium cations are unable to dissolve cellulose, the formate and acetate salts exhibit moderate to excellent solvation of high molecular weight cellulose with a degree of polymerization (DP) of 850. Cellulose undergo a decrease in molecular weight with temperature during dissolution in the 1,2,3-trisubstituted imidazolium acetates devoid of the acidic C2 hydrogen, which is similar to that in 1,3-dialkylimidazolium acetates. Deuterium exchange studies suggest that the cellulose degradation is caused by the increased acidity of the hydrogens at C4 and C5 as well as at C2 methylene of the imidazolium cation. The addition of N-methylimidazole as an organic base suppresses the degradation of cellulose. © 2017 Elsevier B.V.